SPECIFICATION FOR MESSAGE FORMAT FOR
COMPUTER BASED MESSAGE SYSTEMS
National Bureau of Standards
Institute for Computer Sciences and Technology
September 1981
TABLE OF CONTENTS
Page
EXECUTIVE SUMMARY 1
1. INTRODUCTION 3
1.1 Guide to Reading This Document 3
1.2 Vendor-Defined Extensions to the Specification 4
1.3 The Scope of the Message Format Specification 4
1.4 Issues Not Within the Scope of the Message Format 4
Specification
1.5 Relationship to Other Efforts 5
2. A SIMPLE MODEL OF A CBMS ENVIRONMENT 6
2.1 Logical Model of a CBMS 8
2.2 Relationship to the ISO Reference Model for Open 10
Systems Interconnection
2.3 Messages and Fields 10
2.4 Message Originators and Recipients 11
3.2 Message Processing Functions 18
3.2.1 Message creation and posting 19
3.2.2 Message reissuing and forwarding 20
3.2.2.1 Redistribution 22
3.2.2.2 Assignment 22
3.2.3 Reply generation 23
3.2.4 Cross referencing 24
3.2.4.1 Unique identifiers 24
3.2.4.2 Serial numbering 24
3.2.5 Life span functions 25
3.2.6 Requests for recipient processing 25
3.2.6.1 Message circulation 26
3.3 Multiple Occurrences and Ordering of Fields 26
4. SYNTAX 28
4.1 Introduction 28
4.1.1 Message structure 28
4.1.2 Data elements 29
4.1.2.1 Primitive data elements 30
4.1.2.2 Constructor data elements 30
4.1.3 Properties 30
4.1.3.1 Printing-names 30
4.1.3.2 Comments 31
4.1.4 Data compression and encryption 31
4.1.5 Data sharing 31
4.2 Overview of Syntax Encoding 32
4.2.1 Identifier Octets 32
4.2.2 Length code and Qualifier components 33
4.2.2.1 Length Codes 35
4.2.2.2 Qualifier 36
4.2.3 Property-List 38
4.2.4 Data Element Contents 38
4.3 Data Element Syntax 39
4.3.1 Data elements 39
4.3.1.1 Primitives 42
4.3.1.2 Constructors 44
4.3.2 Using data elements within message fields 48
4.3.3 Properties and associated elements 49
4.3.4 Encryption identifiers 49
4.3.5 Compression identifiers 49
4.3.6 Message types 50
SUMMARY OF APPENDIXES 51
ii
APPENDIX A. FIELDS -- IMPLEMENTORS' MASTER REFERENCE 52
APPENDIX B. DATA ELEMENTS -- IMPLEMENTORS' MASTER REFERENCE 57
APPENDIX C. DATA ELEMENT IDENTIFIER OCTETS 65
APPENDIX D. SUMMARY OF MESSAGE FIELDS BY COMPLIANCE 66
CATEGORY
APPENDIX E. SUMMARY OF MESSAGE SEMANTICS BY FUNCTION 68
E.1 Circulation 68
E.2 Cross Referencing 68
E.3 Life spans 68
E.4 Delivery System 68
E.5 Miscellaneous Fields Used Generally 69
E.6 Reply Generation 69
E.7 Reissuing 69
E.8 Sending (Normal Transmission) 69
APPENDIX F. SUMMARY OF DATA ELEMENT SYNTAX 70
APPENDIX G. SUMMARY OF DATA ELEMENTS BY COMPLIANCE CATEGORY 72
G.1 BASIC Data Elements 72
G.2 OPTIONAL Data Elements 72
APPENDIX H. EXAMPLES 74
iii
H.1 Primitive Data Elements 74
H.2 Constructor Data Elements 76
H.3 Fields 81
H.4 Messages 84
H.5 Unknown Lengths 88
REFERENCES 92
INDEX 94
iv
LIST OF FIGURES
FIG. 1. LOGICAL MODEL OF A COMPUTER BASED MESSAGE SYSTEM 8
FIG. 2. MESSAGE FORWARDING AND REDISTRIBUTION 21
FIG. 3. EXAMPLE OF MESSAGE CIRCULATION 27
FIG. 4. STRUCTURE OF IDENTIFIER OCTETS 34
FIG. 5. ENCODING MECHANISM FOR QUALIFIERS AND LENGTH 35
CODES
FIG. 6. REPRESENTATION OF LENGTH CODES 36
FIG. 7. EXAMPLES OF LENGTH CODES 37
FIG. 8. EXAMPLES OF QUALIFIER VALUES 38
v
LIST OF TABLES
TABLE 1. FIELDS USED IN MESSAGE PROCESSING FUNCTIONS 19
TABLE 2. TYPE BITS IN THE IDENTIFIER OCTET 33
vi
Executive Summary
EXECUTIVE SUMMARY
The message format specification addresses the problem of
exchanging messages between different computer-based message
systems (CBMSs). This interchange problem can be addressed on
several levels. One level specifies the physical
interconnections, another specifies how information travels
between CBMSs, another specifies form and meaning of messages
being interchanged. The highest level specifies operations on a
message. Each of these levels would be covered by a different
standard.
This message format specification addresses only the issues
of form and meaning of messages at the points in time when they
are sent from one CBMS and received by another. Messages are
composed of fields, containing different classes of information.
These fields contain information about the message originator,
message recipient, subject matter, precedence and security, and
references to previous messages, as well as the text of the
message. Standard formats (syntax) for messages ensure that the
contents of messages generated by one CBMS can be processed by
another CBMS. Standard meanings (sematics) for the components of
a message ensure standard interpretation of a message, so that
everyone receiving a message gets the meaning intended by its
sender.
Each CBMS that implements this message format specification
will be compatible with any other CBMS that implements the
specification. Compatibility ensures that the contents of a
message posted by one CBMS can be received and interpreted by a
different CBMS.
This message format specification has been developed as a
result of examining CBMSs currently in use in commercial and
research environments. Three major design perspectives helped
shape the message format specification.
o Viability. The message format specification uses
concepts that already work. It has been designed with
implementation concerns in mind.
o Compatibility. The message format specification
contains concepts from existing CBMSs. For this reason,
many CBMS would already contain functions and components
similar to those required to implement the message
format specification.
1
Executive Summary
o Extensibility. This message format specification
defines a broad range of message content components and
requires only an elementary subset of them. This means
that even a very simple CBMS can implement the message
format specification. The message format specification
contains a rich set of optional components and, in
addition, mechanisms for user extensions and future
extensions to the message format specification.
The message format specification defines the form and
meaning of message contents and their components as they pass
from one CBMS to another through a message transfer system. The
message format specification does not address any of the
following major issues.
o Functions or services provided to a user by a CBMS.
For example, the message format specification
assumes that every CBMS allows a user to send and
receive messages. It does not specify any of the
details of how a send function or a message-reading
function might work or how it might appear to the
user. That is, the message format specification
neither limits nor mandates functions.
o Storage or format of message contents in a CBMS.
The message format specification defines the form
and contents of messages when they are transferred
between systems. A CBMS may or may not choose to
use the same format for internal storage.
o Message transfer system protocols.
The message format specification does not specify
how a message travels between CBMSs. It does
specify the form of its contents as it leaves and
arrives, assuming only that the message is moved
transparently by the transfer system.
o Message envelopes.
While a message is traveling between CBMSs, it is
enclosed in a message envelope. Message envelopes
contain all the information about a message that a
message transfer system needs to know. The message
format specification does not define the format or
content of a message envelope.
o How message originators and recipients are identified.
The message format specification does not provide a
representation scheme for the names or addresses of
message originators and recipients as they are
known to a CBMS.
2
Section 1
1. INTRODUCTION
A computer-based message system (CBMS) allows communication
between "entities" (usually people) using computers. Computers
serve both to mediate the actual communications between systems
and to provide users with facilities for creating and reading the
messages.
CBMSs have been developing for over ten years. More
recently, CBMSs have been one of the bases in industry for the
introduction of office automation. A growing number of
organizations use either their own or a commercially available
CBMS. The design and complexity of these systems vary widely.
This message format specification provides a basis for
interaction between different CBMSs by defining the format of
messages passed between them.
1.1 Guide to Reading This Document
The method of presenting the material in this specification
is to combine the technical specification with tutorial
information. This approach has been taken to place the
specification in context and improve its readability.
The core of the technical information in the document is in
Section 2 "A Simple Model of a CBMS Environment", Section 3.1
"Semantics of Message Fields", Section 4.2 "Overview of Syntax
Encoding", and Section 4.3 "Data Element Syntax". Appendixes A
and B consolidate the technical informations. These appendices
are designed for ease of reference and should be read in
conjunction with the body of the report for a complete
understanding of the message format presented in the
specification.
Section 2 presents a simple model of operation of a CBMS.
Section 3 discusses the components of messages and their meaning
(semantics). This includes discussions of the recommended
relationship between message components and CBMS user functions.
(See Section 3.2.) Section 4 presents details of the form
(syntax) required for components of a message.
Appendix D summarizes the components of messages according
to whether they are required or optional for CBMSs implementing
the message format specification. Appendix E organizes the
message components according to the functional class of the
components. Appendix F provides an overview of the syntactic
elements defined by this message format specification; Appendix G
3
Section 1.1
summarizes those elements according to whether they are required
or optional for a CBMS implementing the message format
specification. Examples of each syntactic element appear in
Appendix H, displaying syntax and describing the associated
semantics.
1.2 Vendor-Defined Extensions to the Specification
This specification provides the capability of extending the
range of functionality by the use of vendor-defined qualifiers
and vendor-defined data elements. Any vendor who uses this
capability to provide services which are essentially equivalent
to those already designated as required, basic, or optional does
not comply with the specification.
1.3 The Scope of the Message Format Specification
The purpose of this message format specification is to
present the semantics and syntax to be used for messages being
exchanged between CBMSs. Specifically, it defines the following.
o The meaning and form of standard fields to be used in
messages.
o Which fields must be present in all messages.
o Which fields complying CBMSs must be able to process.
o How messages, fields, and the data contained in fields
are represented.
1.4 Issues Not Within the Scope of the Message Format
Specification
The message format specification does not address the
following issues, some of which are being covered by other NBS
standards developments. (See [BlaR-80] for a description of the
NBS protocols program.)
o The nature of a message transfer system, except to state
the assumption that it transfers messages transparently.
4
Section 1.4
o The form or nature of the protocols used to transfer
messages (posting, relay, and delivery protocols).
o The content and representation of message envelopes.
o Representations for unique identifiers (in particular,
message identifiers).
o Network and internetwork addressing.
o Representations for identities of message originators
and recipients.
o Functions that CBMSs provide for users.
o Presentation of messages to users.
o Representations for multi-media objects.
o Data representation for messages within CBMSs.
o Data sharing or any storage management within CBMSs.
o Representations for fixed or floating point numbers.
1.5 Relationship to Other Efforts
The message format specification is based on several
documents and the current state of many CBMSs available both in
industry and the research community. These documents include the
standardization efforts in the ARPANet [CroD-77, PosJ-79] and the
CCITT, proposed ISO and ANSI header format standards [TasG-
80, ISOD-79], the work of IFIPS Working Group 6.5, and various
papers about the general nature of mail systems, addressing, and
mail delivery. (See [FeiE-79] for references.
5
Section 2
2. A SIMPLE MODEL OF A CBMS ENVIRONMENT
In order to provide a framework for presenting the message
format specification, this section describes a simple functional
model for a CBMS. The model provides a high-level description of
both user facilities and system architecture. Discussions of
messages, message originators and message recipients serve to
further clarify the nature of a CBMS.
A CBMS permits the transfer of a message from an originator
to a recipient. "Originator" and "recipient" are used in their
normal English senses. (See Section 2.4.) A message (in its
most abstract definition) is simply a unit of communication from
an originator to a recipient. A CBMS offers several classes of
functions to its users:
o Message Creation: The facilities used by a message
originator to create messages and specify to whom they
are to be sent.
o Message Transfer: The facilities used to convey a
message to its recipient(s).
o Recipient Processing: The facilities used by a message
recipient to process messages that have arrived.
These classes of functions are presented in more detail in
Section 3.2.
CBMSs differ from other office automation/communications
systems in a number of ways.
o Unlike other types of electronic communications, CBMS
messages are sent to particular individuals, not to
stations or telephone sets. If a recipient moves to a
different location, messages sent to that recipient are
delivered to the recipient at the new location.
o Transmission of CBMS messages is asynchronous. The
recipient's system need not be available when the
message leaves the originator's system. That is, CBMS
message transfer facilities are store-and-forward.
o CBMS messages can contain a wide variety of data. They
are not constrained to any single kind of communication.
CBMS messages are often simple memoranda but are not
restricted to text. A CBMS message may contain any kind
6
Section 2
of data that an originator wishes to send to a
recipient. By contrast, Teletex systems and
communicating word processors handle the transfer of
final form documents; compatible communicating word
processors can exchange documents in editable form;
Telex and TWX deal in unformatted text.
o CBMSs offer message creation facilities as an important
part of the system. CBMSs assist users in the
preparation of messages by having text editing
facilities available and allowing users to include data
stored on-line in messages. Some CBMSs also interface
to other office automation facilities, such as
formatters and spelling correctors. This is not true of
Telex, TWX, or similar services.
o CBMSs offer recipient processing facilities as an
important part of the system. This is not true of most
other forms of electronic communications. For example,
Telex and TWX systems simply print messages on paper
when they are received, without retaining a copy in the
system. (Teletex systems are similar to Telex systems,
but some can retain a copy of the document in local
storage.) Communicating word processors might notify
their operators that a document has been received and is
stored on-line, but offer little in the way of other
recipient processing facilities. Most CBMSs offer at
least the following recipient processing facilities.
. The ability to retain a copy of a message on-line
after it has been read.
. The ability to examine or delete stored messages
individually.
. The ability to organize messages using some form of
electronic "file folder".
. The ability to determine if a message is recent
(has arrived since the last time the recipient used
the CBMS) or unseen (has never been examined by the
recipient).
. The ability to summarize stored messages. A
summary usually includes information such as
whether the message is recent or unseen, when it
was received, its length, who it is from, and its
subject.
. The ability to retrieve a stored message based upon
7
Section 2
one or more of its attributes (for example, when
the message was received, whether or not it has
been seen or deleted, and the values contained in
its fields).
. A forward facility that allows users to include all
or part of a message in a new outgoing message.
. A reply facility that allows users to answer
messages without having to enter a new list of
recipients.
2.1 Logical Model of a CBMS
CBMS facilities for message creation, transfer, and
recipient processing are reflected in a logical model of a CBMS
developed by IFIP Working Group 6.5 [SchP-79]. (An essentially
identical model is being used by CCITT Study Group VII, Question
5, regarding Message Handling Facilities.) The model consists of
a Message Transfer System and a number of User Agents. (See
Figure 1.)
FIG. 1. LOGICAL MODEL OF A COMPUTER BASED MESSAGE SYSTEM
A User Agent is a functional entity that acts on behalf of a
user, assisting with creating and processing messages and
communicating with the Message Transfer System.
The Message Transfer System] is an entity that accepts a
8
Section 2.1
message from its originator's User Agent and ultimately passes it
to each of its recipients' User Agents. The Message Transfer
System may perform routing and storage functions (among others)
in order to accomplish its task.
Transferring a message from an originator's User Agent to
the Message Transfer System is called Posting; the originator's
User Agent and Message Transfer System engage in a Posting
Protocol in order to accomplish Posting. Transferring a message
from the Message Transfer System to a recipient's User Agent is
called Delivery; the recipient's User Agent and Message Transfer
System engage in a Delivery Protocol in order to accomplish
Delivery.
The point at which responsibility for a message is
transferred is called a Slot. The Posting Slot is the point at
which responsibility for a message passes from an originator's
User Agent to the Message Transfer System; the Delivery Slot is
the point at which responsibility for a message passes from the
Message Transfer System to a recipient's User Agent.
The model divides messages into two parts, the message
content and the message envelope. The message content is the
information that the originator wishes to send to the recipient;
this message format specification deals solely with the message
content. The message envelope consists of all the information
necessary for the Message Transfer System to do its job; this
message format specification does not specify the message
envelope. Some of the data appearing on the message envelope
could be redundant with some data found in the message content.
The Message Transfer System is not expected to examine the
message content unless it is told to do so by the originator's or
recipient's User Agent.
This message format specification places no restrictions on
the Message Transfer System itself, except that it be transparent
to the contents of messages. In addition, this message format
specification does not dictate the form or nature of any protocol
used by the Message Transfer System. Finally, this message
format specification does not specify the content or form of the
message envelope. That is, the message format specification
defines the format for the contents of messages, not the manner
in which they are transmitted.
Many of today's commercially available CBMSs incorporate all
of the facilities represented in the logical model. Their
architectures may reflect the economies that can be taken when
implementing systems that are self-contained. For example,
stand-alone systems that store messages in a single central
database require no Message Transfer System; an implementation
may integrate software for User Agent and Message Transfer System
functions, doing away with Posting or Delivery Protocols.
9
Section 2.1
2.2 Relationship to the ISO Reference Model for Open Systems
Interconnection
Subcommittee TC97/SC16 of the International Standards
Organization (ISO) has developed a reference model for describing
communications between "open" systems [ISOD-81]. This model is
known as the ISO Reference Model for Open Systems Interconnection
(OSI). It divides communications protocols into seven layers,
ranging from physical interconnection at the lowest layer to data
exchange by application programs at the top.
This message format specification deals with data used by an
application within a system. Thus, the message format being
specified here is not a protocol. Since it is not a protocol, it
lies outside of the model for open systems interconnection. User
Agents are application layer entities (layer 7), however, and the
protocols used by a message transfer system are above the session
layer (layer 5).
2.3 Messages and Fields
A message is a unit of communication from an originator to a
recipient. A message consists of a series of components called
fields. Fields can be described according to their meaning in a
message (semantics) and according to the format required for them
in a message (syntax).
Semantically, a field is just a component of a message; the
meanings of particular fields are defined by this message format
specification. Syntactically, a field is a unit of data whose
form is defined by this message format specification. Additional
fields can be defined by users or vendors as long as they conform
to the syntactic and semantic rules that this message format
specification defines for additional fields.
(A note on terminology: A message consists of components
called fields. The words "message" and "field" are used both in
the informal sense of the previous sentence and in a more
restricted sense as names of particular syntactic elements. As
syntactic element names, Message and Field are always
capitalized.)
Some CBMS functions are based on the contents of particular
fields; other functions (such as the ability to read a message)
may have little to do with the fields themselves. Section 3.2
discusses some of the specific functions that a CBMS might
provide to users and the fields that must be used to support
those functions.
10
Section 2.3
2.4 Message Originators and Recipients
This message format specification refers to message
originators and recipients. These terms were defined
functionally in Figure 1. When the message format specification
refers to the identity of a message originator or recipient, it
means "that information which uniquely identifies the message
originator or recipient within the domain of the given message
system." The syntax and semantics of message addressing are not
within the scope of the message format specification.
Originators and Recipients can be people, roles, or
processes.
People. People as originators and recipients are specific
individuals.
Roles. Roles identify functions within organizations as
opposed to the specific individuals who perform them. For
example, consider a newspaper that produces both morning and
evening editions and therefore operates with more than one shift.
Someone wishing to contact the city desk would send a message to
the city desk role rather than trying to determine exactly who
was assigned to the city desk at a specific time. (Of course,
messages can usually be sent to the individuals directly whether
or not they are actually performing a role at the time.)
Processes. A process in a computer could serve as either an
originator or a recipient for messages. A computer system might
originate a message to notify a recipient about the status of
some task. For example, an archive utility could notify users
about files that have been archived; a distributed file system
could notify a user that a remote file has been deposited on a
local file system. Messages could be used by computer systems to
warn about some impending condition or even to monitor the
performance of the computer itself. Some computer processes may
also be message recipients, taking action based upon message
contents.
In addition, some CBMSs allow messages to be sent to groups.
A group is a predefined list of message recipients. Using a
group name as a recipient permits message originators to
designate a potentially large number of recipients using a single
recipient identifier. This makes using the CBMS more convenient
and accurate.
11
Section 3
3. SEMANTICS
This section discusses two major topics, message processing
functions and message field meanings. Section 3.1 describes the
six functional groups of message fields. The functional groups
are Origination, Dates, Recipients, Cross-referencing, Message-
handling, and Message-contents. They are explained more fully in
Section 3.1.1, along with detailed discussion of the semantics of
all the fields in each functional group. Section 3.2 describes
message processing functions whose operation is based on the
meanings of particular message fields.
3.1 Semantics of Message Fields
The definition of a message is discussed generally in
Sections 1 and 2. Semantically valid messages must contain one
From field, one To field, and one Posted-Date field. They may
contain, in addition, any number of other fields, depending on
the processing and functions supplied by the originating or
receiving CBMS. (Section 3.2 describes classes of functions
supplied by CBMSs.)
3.1.1 Types of fields
Message receiving programs are required to interpret fields
according to the semantics described in the remainder of this
se. The message fields defined in this document are grouped
into the following functional categories.
o Originator fields indicate who or what participated in
the creation of the message and where replies should be
directed. (See Section 3.1.3.)
o Date fields record when events take place, for a variety
events, such as message creation or expiration. (See
Section 3.1.5.)
o Recipient fields indicate who or what is intended to
receive a message. (See Section 3.1.4.)
o Cross-reference fields label a message or refer to other
messages. (See Section 3.1.6.)
o Message-handling fields record the type of service a
12
Section 3.1.1
message's sender requested of a message transfer system
or indicate how the message should be treated by its
recipients. (See Section 3.1.7.)
o Message-content fields either contain the primary
content of a message or index or summarize it. (See
Section 3.1.8.)
o Extension fields provide mechanisms for extending the
message format specification. (See Section 3.1.9.)
3.1.2 Semantic Compliance Categories
For purposes of determining whether a CBMS complies with the
semantic requirements of this message format specification,
message fields have been divided into three categories:
REQUIRED These fields must be present in all messages and must
be processed by message receiving programs as defined
by the message format specification.
BASIC These fields need not be present in all messages but
when they do appear they must be processed by message
receiving programs as defined by the message format
specification.
OPTIONAL These fields need not be present in all messages and
may be ignored by message receiving programs. The
exact meaning of "ignored" is not specified by the
message format specification. In general, a CBMS must
recognize the existence of an optional field (that is,
optional fields should not cause errors) and must not
process the field in a manner contrary to the semantics
defined for that field by the message format
specification.
(Syntactic compliance is defined in Section 4.1.2.)
3.1.3 Originator fields
A message originator may be a person, role, or process.
Originator fields identify a message's author, who is responsible
for the message, who or what sent it, and where any
replies should be directed. (See Section 2.4.)
13
Section 3.1.3
From (REQUIRED)
This field contains the identity of the originator(s)
taking formal responsibility for this message. The
contents of the From field is to be used for replies
when no Reply-to field appears in a message.
Reply-To (BASIC)
This field identifies any recipients of replies to the
message.
Author (OPTIONAL)
This field identifies the individual(s) who wrote the
primary contents of the message. Use of the Author
is discouraged when the contents of the Author
field and the From field would be completely redundant.
Sender (OPTIONAL)
This field identifies the agent who sent the message.
It is used either when the sender is not the originator
responsible for the message or to indicate who among a
group of originators responsible for the message
actually sent it. Use of the Sender field is
discouraged when the contents of the Sender field and
From field would be completely redundant. Only one
Sender field is permitted in a message.
3.1.4 Recipient fields
Message recipients may be people, roles, or processes. (See
Section 2.4). Recipient fields identify who or what is to
receive the message.
To (REQUIRED)
This field identifies the primary recipients of a
message.
Bcc (OPTIONAL)
This field identifies additional recipients of a
message (a "blind carbon copies" list). The contents
of this field are not to be included in copies of the
message sent to the primary and secondary recipients.
See section 3.2.1 for further discussion of the use of
blind carbon copies lists.
Cc (BASIC)
This field identifies secondary recipients of a message
(a "carbon copies" list).
14
Section 3.1.4
Circulate-Next (OPTIONAL)
This field is used in conjunction with the Circulate-To
field. (See Section 3.2.6.1.) It identifies all
recipients in a circulation list who have not received
the message.
Circulate-To (OPTIONAL)
This field identifies recipients of a circulated
message. (See Section 3.2.6.1.) It is used in
conjunction with the Circulate-Next field.
3.1.5 Date fields
Date fields for two kinds of uses are provided. Dates can
be associated with some event in the history of a message and
dates can delimit the span of time during which the message is
meaningful (its life span).
Posted-Date (REQUIRED)
This field contains the posting date, which is the
point in time when the message passes through the
posting slot into a message transfer system. Only one
Posted-Date field is permitted in a message.
Date (OPTIONAL)
This field contains a date that the message's
originator wishes to associate with a message. The
Date field is to the Posted-Date field as the date on a
letter is to the postmark added by the post office.
End-Date (OPTIONAL)
This field contains the date on which a message loses
effect. (See also Section 3.2.5.)
Received-Date (OPTIONAL)
Delivery date. This field may be added to a message by
the recipient's message receiving program. It
indicates when the message left the delivery system and
entered the recipient's message processing domain.
Start-Date (OPTIONAL)
This field contains the date on which a message takes
effect. (See also Section 3.2.5.)
Warning-Date (OPTIONAL)
This field is used either alone or in conjunction with
an End-Date field. It contains one or more dates.
These dates could be used by a message processing
15
Section 3.1.5
program as warnings of an impending end-date or other
event. (See also Section 3.2.5.)
3.1.6 Cross-reference fields
Cross reference fields can be used to identify a message and
to provide cross references to other messages. (See Section
3.2.4.)
In-Reply-To (OPTIONAL)
This field designates previous correspondence to which
this message is a reply. The usual contents of this
field would be the contents of the Message-ID field of
the message(s) being replied to.
Message-ID (OPTIONAL)
This field contains a unique identifier for a message.
This identifier is intended for machine generation and
processing. Further definition appears in Section
3.2.4.1. Only one Message-ID field is permitted in a
message.
Obsoletes (OPTIONAL)
This field identifies one or more messages that this
one supplants.
Originator-Serial-Number (OPTIONAL)
This field contains one or more serial numbers assigned
by the message's originator. Messages with multiple
recipients should have the same value in the
Originator-Serial-Number field.
References (OPTIONAL)
This field identifies other correspondence that this
message references. If the other correspondence
contains a Message-ID field, the contents of the
References field must be the message identifier.
3.1.7 Message-handling fields
Message-handling fields describe aspects of how a message is
to be handled or categorized.
Precedence (OPTIONAL)
This field indicates the precedence at which the
message was posted. Ordinarily, message precedence or
priority is a service request to a message transfer
16
Section 3.1.7
system. A message originator, however, can include
precedence information in a message. One example of
precedence categories are those used by the U.S.
Military: "ROUTINE", "PRIORITY", "IMMEDIATE", "FLASH
OVERRIDE", and "EMERGENCY COMMAND PRECEDENCE".
Message-Class (OPTIONAL)
This field indicates the purpose of a message. For
example, it might contain values indicating that the
1
message is a memorandum or a data-base entry.
Reissue-Type (OPTIONAL)
This field is used in conjunction with message
encapsulating (see Section 2.4.1) to differentiate
between messages being assigned or redistributed.
Received-From (OPTIONAL)
This field contains a record of a message's path
through a message transfer system. The
recipient's message receiving program could store here
any information about the transfer that it obtained
from a message transfer system.
3.1.8 Message-content fields
The intent of most messages is to communicate some
particular information from originator to recipient. Several
fields in a message are designed to contain that information.
Subject (BASIC)
This field contains any information the originator
provided to summarize or indicate the nature of the
message.
Text (BASIC)
This field contains the primary content of the message.
Attachments (OPTIONAL)
This field contains additional data accompanying a
message. It is similar in intent to enclosures in a
conventional mail system.
_______________
1
The message format specification is not intended to be used as
a specification for exchanging data-base records. Messages,
however, sometimes contain data from or for a database.
17
Section 3.1.8
Comments (OPTIONAL)
This field permits adding comments to the message
without disturbing the original contents of the
message.
Keywords (OPTIONAL)
This field contains keywords or phrases for use in
retrieving a message.
3.1.9 Extensions
This message format specification allows two additional
types of fields, vendor-defined fields and as-yet-undefined
(extension) fields that will be introduced by extensions to this
message format specification.
vendor-defined-field
Any field not defined in this message format
specification or any extension or successor to it is a
vendor-defined field. Names for vendor-defined fields
could be preempted by extensions to this message format
specification.
extension-field
Any field that is defined in a document published as a
formal extension or replacement to this message format
specification.
3.2 Message Processing Functions
A CBMS provides three basic classes of functions, creating
messages, transmitting messages to their recipient, and post-
receipt processing. Although the message format specification
does not define the number or nature of user functions in CBMSs,
the meanings for the fields clearly assume certain kinds of
functions. For example, fields specifying recipients of replies
to messages assume some kind of reply function; fields specifying
message life span assume some kind of date processing functions.
This section provides more detail on the processing that
might be done by these kinds of functions, discussing the message
fields that would be used and how they would be used. (See
summary in Table 1.)
TABLE 1. FIELDS USED IN MESSAGE PROCESSING FUNCTIONS
3.2.1 Message creation and posting
Messages can be created either by reissuing an existing
message to a new recipient (see Section 2.4.1) or by creating a
new message. The process of message creation might mean that
some fields of a new message are filled in from the contents of
some other message. Reply functions (Section 3.2.3) provide an
example of this.
Different individuals could be involved in different phases
of originating a message: creating it, taking responsibility for
it, and explicitly interacting with a CBMS to send it to its
recipient. One or more individuals may create (that is, write,
but not necessarily enter into the CBMS) a message; they are said
to be the message's authors, identified by the Author field. One
or more individuals may take responsibility for its contents and
the decision to post it; they are identified by the From field.
One individual explicitly posts a given message; this person is
called the message's sender (identified by the Sender field).
The sender and author(s) are often, but not always,
responsible for the message. A common case in which the sender
is not responsible for the message is when a secretary enters and
posts messages for someone else. An example of a situation in
which a message's author is not responsible for the message
itself is when an administrative assistant prepares a report that
is sent under a manager's signature.
Messages containing Bcc fields are treated specially by
CBMSs. The contents of this field are not included in copies of
the message sent to the recipients designated in the To and Cc
fields. Some systems include the contents of the Bcc field only
19
Section 3.2.1
in the originator's copy, others include include all or part of
the Bcc field in the copies sent to the recipients indicated in
the Bcc field. This specification does not mandate how the Bcc
field is to be treated.
Audit trail entries (such as the posting time and sender
identity) are automatically appended to a message by the CBMS
each time the message passes through a posting slot to a message
transfer system; a message transfer system could also provide
timestamps at each transfer between user agent and the transfer
system. A message identifier (Sections 3.2.4 and 3.1.6), placed
in the message by the original sender's User Agent, is preserved
throughout this message flow. This means that when the same
message is sent twice to the same recipients by the same Sender,
the audit trail information for the two messages is different.
3.2.2 Message reissuing and forwarding
Reissuing and forwarding both serve the general user goal of
passing a message on to a new set of recipients. Forwarding is
the term used for an informal mechanism, which CBMSs implement by
copying some or all of the original message into the contents of
a field in the new message. Reissuing is the term used for a
formal mechanism to ensure that the message being passed on never
loses its integrity as a previously sent message. CBMSs use
reissuing to implement several different functions, depending on
the purposes being served.
o Redistribution. Make others aware of the complete and
unaltered contents of the message.
o Assignment. Delegate the responsibility for a message
to somebody else.
These purposes are exemplified in Figure 2.
When a CBMS examines a forwarded message, it cannot always
distinguish the old message from what was added when the
forwarding took place. In addition, the forwarded information
might no longer have the form of a message. This is usually
because the format of the message has been changed (for example,
to pure unformatted text). (See Figure 2 for an example of how a
CBMS might forward a message.) In contrast, a reissued message
can always be separated from its enclosing message and never
loses its identity as a correctly formed message.
This specification provides the Reissue-Type field for
20
Section 3.2.2
The Original Message
John Doe wishes Jane Jones to get a copy of the following
message:
Message:
Field: From "Jean Smith"
Field: Posted-Date "15 June 1980"
Field: To "John Doe"
Field: Subject "Next sales meeting"
Field: Text "The agenda for ..."
Redistribution
Message:
Field: From "John Doe" John Doe is responsible
Field: Posted-Date "16 June 1980" for the redistribution.
Field: To "Jane Jones"
Field: Reissue-Type "Redistribution" This message directly
Message: incorporates a
Field: From "Jean Smith" redistributed message.
Field: Posted-Date "15 June 1980"
Field: To "John Doe"
Field: Subject "Next Sales Meeting"
Field: Text "The agenda for ..."
Forwarding
Message:
Field: From "John Doe"
Field: Posted-Date "16 June 1980"
Field: To "Jane Jones"
Field: Text A realization of the
"From Jean Smith original message is
To John Doe copied into the Text field.
Sent on 15 June 1980 Note that John's CBMS
Subject Next Sales Meeting has chosen to represent
it as a text string.
The agenda for ..."
FIG. 2. MESSAGE FORWARDING AND REDISTRIBUTION
21
Section 3.2.2
supporting re-issuing. Forwarding, since it is an informal means
of serving the purpose of passing on information, has no
supporting fields in the specification.
This specification provides for reissuing of messages by
encapsulating. This method embeds the entire original message
inside a new message. Encapsulating adds structure around the
2
message . This allows any part of it to be easily extracted.
Authentication is an organizational policy issue associated
passing on previously sent messages. Each organization must
decide if the CBMS it acquires should support reissuing or simply
supply forwarding.
3.2.2.1 Redistribution
Redistribution is a CBMS function for sending the original
contents of a message intact and unchanged to new recipients. A
redistributed message is identical to the original message with
the exception of added information about the reissuing. For
reissuing with this purpose, the Reissue-Type field contains the
ASCII string "Redistribution". The original message has been
included directly in a new message. (See Figure 2.)
3.2.2.2 Assignment
Assignment is the process of designating responsibility. In
some organizations, formal message traffic is funneled through
one or more parts of the organization (called offices) where it
is directed to the appropriate individuals or other offices for
final disposition. Assignment is done by reissuing a message
with the Reissue-Type field containing the ASCII string
"Assigned." A message which contains this field is to be
interpreted as meaning that the addressees in the "To" field have
had the reissued message assigned to them for some action. Any
addressee in the "Cc" field has had the message assigned for
information. The "From" field records who assigned the message
and the "Posted-Date" field records when the message was
assigned.
_______________
2
A message can contain another message, and that message can
contain another message, and so on to any depth of encapsulating.
This can occur by reissuing a message repeatedly.
22
Section 3.2.3
3.2.3 Reply generation
Reply generation involves creating a new message in direct
reply to some other message by drawing on the contents of fields
in the other message to fill fields in the new message. Many
CBMSs provide reply facilities that determine the intended
recipients of a reply to a message.
o A Reply-To field is defined by this message format
specification. When a message contains a Reply-To
field, the CBMS should send replies to the recipients
designated in the Reply-To field instead of to the
recipients designated in the From field. This statement
applies to original messages only, not to reissued
messages. The message format specification makes no
recommendations concerning replies to reissued messages.
Reply-To has several possible applications.
1. The individual(s) responsible for the message
might not have regular access to a CBMS and would
indicate an alternate recipient, for example, a
secretary.
2. The people responsible for receiving responses
might not be the people who were responsible for
creating the message.
3. Discussion and conference groups could use this
feature to ensure correct distribution of any
submission by having the conference group itself
designated in the Reply-To field.
o When the message does not contain a Reply-To field, the
recipient should reply to the originators enumerated in
the From field. The sender and authors should not be
added automatically to the list of those receiving the
reply.
Replies could also be sent to the other recipients of the
original message. Vendors might offer additional reply
facilities, depending on their view of users' organizational
requirements.
23
Section 3.2.4
3.2.4 Cross referencing
A CBMS message may include designator(s) which identify
other message(s). The designators are used to refer to related
messages so that all information in a chain of correspondence can
be determined by a CBMS user. The designator used to identify
and cross-reference messages can take either of two forms, unique
identifiers or serial numbers.
3.2.4.1 Unique identifiers
Unique identifiers are machine-generated quantities that are
intended primarily for processing by computers. While they could
be examined by a human user, unique identifiers are not
necessarily useful or convenient for people.
Unique identifiers occur in several contexts. They are
often used to identify the contents of individual messages
unambiguously. When unique identifiers are used this way, they
are called message identifiers. Different versions of a message
(for example, the message when it is reissued with comments)
receive new message identifiers.
When a CBMS generates a message identifier, it must be able
to guarantee that it is unique, both within the domain of the
individual CBMS and globally, across all connected CBMSs. CBMSs
could generate globally unique identifiers in several ways, all
of which require prior agreement on behalf of the connected
CBMSs. One method is to assign each connected CBMS a unique
code. A CBMS then generates unique identifiers by using its code
as a prefix to some other quantity that it can guarantee to be
unique within its domain. (This second quantity could be a
counter or a timestamp/user-id combination.)
A CBMS can provide functions for tracing chains of
correspondence by using unique identifers. The message format
specification defines fields for which a CBMS provides unique
identifiers as values. They are Message-ID, References,
Obsoletes, and In-Reply-To. (See Section 3.1.6.)
3.2.4.2 Serial numbering
Serial numbers are for users to maintain a personal
numbering system for messages. The numbers are composed of both
letters and digits so that users could maintain several sets of
sequences concurrently (for example, A1, A2, A3... and B1, B2,
B3...).
24
Section 3.2.4.2
Serial numbers are assigned at a defined point in the
history of a message. Serial numbers are not unique identifiers;
they differ from unique identifiers (Section 3.2.4.1) in that
they are not necessarily either generated or processed by a CBMS.
They are designed to be typed and read by CBMS users. They can
be as simple or complex as the user requires. Serial numbers are
intended to be used to designate messages about a specific topic,
or messages a given user has sent. Serial numbers are intended
to be a permanent part of the message, just as unique identifiers
are.
A CBMS can provide functions allowing originators to add
serial numbers to messages. A field has been provided to permit
this. Originator-Serial-Number is for an originator to add a
serial number to a message before sending it.
3.2.5 Life span functions
Messages have life spans, usually delimited by the creation
date and the time when the last copy of the message is destroyed.
Messages could be meaningless before a certain time or irrelevant
after a certain time. For example, a reminder to attend a
meeting on 5 June loses most of its value on the sixth; a
reminder to attend that same meeting is likely to be of little
use on 5 May (although not for the same reason).
A CBMS can define a message's life span explicitly using the
Start-Date and End-Date fields. A third field, Warning-Date,
when used in conjunction with the End-Date, may be used to signal
the approach of the End-Date. It may also stand alone and be
used by a periodic warning (alarm clock) mechanism.
A CBMS could use these fields to help users manage their
message stores. For example, a message whose start date has not
yet passed could be bypassed by a retrieval command unless the
user requested such messages explicitly. A CBMS could use the
end date to help with message store housekeeping either by
archiving or deleting the expired messages automatically or by
asking the user for some action to be taken on them. The warning
date could be used to automatically remind the user of an
impending end date, such as a meeting reminder.
3.2.6 Requests for recipient processing
Recipients have a wide variety of needs for examining and
processing a message, ranging from automatic output on some
specified device to the execution of a program embedded in the
25
Section 3.2.6
message itself. Because many of these needs are highly
specialized, and support for them not widely implemented, this
message format specification does not constrain the requests for
processing that may be included in a message.
The message format specification does provide two fields
that permit an originator to request circulation list processing
from the recipient. These fields are Circulate-To and Circulate-
Next.
3.2.6.1 Message circulation
Message circulation involves serial distribution of a
message to its recipients, based on a distribution list that is
part of the message. The message is delivered first to the first
recipient on the distribution list. This recipient, or someone
the recipient delegates, sends the message on to the second
recipient on the list, perhaps after commenting on or adding to
the message. This continues until all recipients on the
distribution list have received the message.
This message format specification provides two fields to
support message circulation. The Circulate-To field contains the
complete distribution list, indicating the full set of
recipients, and the Circulate-Next field indicates which
recipients have not seen the message. See Figure 3 for an
example of message circulation using these two fields.
3.3 Multiple Occurrences and Ordering of Fields
Most message fields may occur more than once in a message;
the exceptions are the Posted-Date, Sender, and Message-ID
fields, which may occur at most once. What this means is that a
received message may contain any number of instances of a
particular field (such as the "To" field). If a message contains
more than one instance of a particular field, that field "occurs
multiply" and that message has "multiple occurrences" of that
field.
A particular instance of a message field is not superseded
by later instances of the same field. The To field is an example
of this.
Multiple occurrences of a field are not necessarily
equivalent to a single field containing the concatenated contents
of the several instances of the given field. For example, with
the Text field, concatenating the contents of several instances
26
Section 3.3
-----------------------------------------------------------------
A message originator wishes to circulate a message to
recipients A, B and C. The originator includes the
following fields in the message:
To: A
Circulate-To: A, B, C
Circulate-Next: B, C
When recipient A or somebody A delegates causes the
message to be further circulated, the message is sent
to the first address in the Circulate-Next field, and
that name is removed from that field:
To: B
Circulate-To: A, B, C
Circulate-Next: C
B now sends the message on to its final recipient:
might lose important distinctions between the contents. A single
message could be used to send three different documents, each one
in a different Text field. However, putting the three documents
into a single Text field would make it much more difficult to
extract any individual document.
The fields found in a single message may occur in any order.
The order in which they occur does not necessarily reflect the
order in which they were created. Nor does it constrain the
order in which the message recipient examines, processes, or
displays them.
27
Section 4
4. SYNTAX
This section begins with an introduction to the concepts and
elements that constitute the syntax for messages. The second
section presents an overview of the encoding scheme. The third
section describes in detail the elements of the message syntax.
4.1 Introduction
This specification defines syntactic requirements for
messages when they are passed from one CBMS to another. The
specification is designed to meet the following goals.
o Provide a concise flexible representation scheme.
o Simplify message parsing.
o Support non-textual components in messages (for example,
3
facsimile, graphics, or speech ).
4.1.1 Message structure
Messages have two classes of components, fields and
messages. A field corresponds to one of the semantic components
defined in this message format specification. A message is
simply another message.
The type of a field in a message determines both its meaning
and the form for its contents. (See Section 4.3.2.)
Fields in a message are composed of syntactic elements
called data elements. A Message data element is used to
represent messages; a Field data element is used to represent
fields. (The term "field" is simply a semantic construct,
distinct from "Field Data Element", which is a syntactic
_______________
3
While this message format specification is not intended to be
used as a basis for the intnge of all facsimile information,
it does recognize that CBMS messages may contain facsimile
components.
28
Section 4.1.1
construct.) Many of the fields defined in this message format
specification estricted to containing only one kind of data
element. (See Section 4.3.2.)
Each field defined in this message format specification has
been assigned a unique numeric identifier that is used in
conjunction with the Field data element. Separate identifiers
are provided for vendor-defined fields and for extending the
identifier encoding space. A list of fields and identifiers
appears in Section 4.3.2 and in Appendix C.
Throughout the message format specification, fields are
referred to by label name rather than by their numeric
identifiers. Field labels are names like "Sender", "Warning-
Date", or "Circulate-To". The field labels chosen for the
specification are names that are in common use in current CBMSs.
The specification does not require a CBMS to use these field
labels in displaying fields to the user, although such usage is
encouraged to provide a common user interface.
4.1.2 Data elements
For the purpose of determining compliance with the syntax
defined in this specification, data elements are divided into two
groups, basic and optional.
BASIC All message receiving systems must process these
syntactic elements, interpreting their values according
to the message format specification.
OPTIONAL Message receiving systems need not process these
syntactic elements in order to be in compliance.
In addition, complying CBMSs must meet requirements
regarding their ability to process the components found inside
data elements. These requirements are discussed in Section
4.2.2. (Semantic compliance is defined in Section 3.1.2.)
This message format specification classifies data element
types as either primitives or constructors. (See Sections
4.1.2.1 and 4.1.2.2.) Primitive data elements, such as ASCII-
String, are basic building blocks. Constructor data elements,
such as Message or Sequence, contain one or more primitive or
constructor data elements. Some constructors, such as Sequence,
may be composed of any other data element. Some, such as
Message, may contain only certain data elements. (See Section
4.3.1.)
29
Section 4.1.2.1
4.1.2.1 Primitive data elements
A primitive data element contains a basic item of
information; it is not composed of other data elements. In
current CBMSs, the most commonly used primitive data element is
ASCII-String, a series of ASCII characters. Other primitive data
elements are Integer, 2's complement integers; Bit-String, a
series of bits; and Boolean, either True or False.
One primitive data element, End-Of-Constructor, is used only
as a structural element within constructor data elements and has
no meaning by itself. End-of-Constructor is used to provide an
end marker for constructor data elements that do not have an
explicit length. (See Section 4.2.2.1.) Any other use is not
valid syntactically.
4.1.2.2 Constructor data elements
The Data Element Contents of constructor data elements
contain one or more data elements. The most general form of a
constructor is a Sequence or a Set, since both Sequences and Sets
may contain any data element. Other constructors are specialized
forms of sequences.
A Message data element is a constructor. It may contain
only Field data elements, other Message data elements, or
encrypted or data compressed forms of these elements. A Field
data element can contain any data element. It also indicates
which specific field is being represented. The contents of some
fields are restricted to a single type of data element, such as
ASCII-String or Date.
4.1.3 Properties
Any data element may have associated with it a Property-
List, which contains properties such as a Printing-Name (Section
4.1.3.1) or one or more Comments (Section 4.1.3.2). A mechanism
to support vendor-defined properties has been supplied by this
specification, as well as a mechanism to extend the list of
property identifiers.
4.1.3.1 Printing-names
Printing-Names are used to provide labels that can be
displayed along with their respective data elements. For
example, a message originator may use a Printing-Name property to
request that the To field of a message be labeled "Distribution:"
when it is printed by its recipients.
30
Section 4.1.3.1
4.1.3.2 Comments
The Comment property is used to allow comments to be
associated with any data element without affecting its actual
contents. For example, someone reviewing the text of a message
could add the comment "This looks good" to the Text field without
either altering the body itself or adding a separate comment
field.
4.1.4 Data compression and encryption
Two constructor data elements, Compressed and Encrypted,
have been provided for use by a CBMS that supports data
compression or encryption. They may be used to hold the
compressed or encrypted contents of any data element, including
Messages and Fields, and may occur wherever their compressed or
encrypted contents may appear. A mechanism is included to allow
the user to identify the encryption or compression algorithm used
(Sections 4.3.4 and 4.3.5).
4.1.5 Data sharing
Data sharing is the multiple use of a data element via
references to a single copy. It is used in two situations.
o For economy when a large object appears more than once
in a message. Data sharing may be used in this
situation to economize on storage and transmission
costs.
o For consistency when the same object appears more than
once in a message. If one instance of that object is
altered, all instances must reflect this alteration. In
this case several copies of the same object will not
serve the purpose as well as data sharing.
While there is a demonstrable need for facilities to support
data sharing, this specification does not define such a
mechanism. At this time there is insufficient experience with
data sharing in messages to allow standardization. The
specification is sufficiently flexible however to allow
extensions to the syntax for supporting data sharing at a later
time.
31
Section 4.2
4.2 Overview of Syntax Encoding
This section provides an overview of the notation and
terminology used to represent the syntactic elements (data
elements) defined in this message format specification.
All data elements consist of a series of components. Each
of the components is composed of a series of 8-bit groups called
octets. In this document, the bits are numbered starting from
the low-order bit. That is, the low-order (or least significant)
bit is called "bit 0" and the high-order (or most significant)
bit is called "bit 7".
Five different components may appear in a data element.
o Identifier octet (identifying particular type of data
element)
o Length Code (specifying number of octets that appear
following it in a data element)
o Qualifier (supplying additional identifying information)
o Property-List component (a Property-List data element
containing Property data elements)
o Data Element Contents (containing actual data of the
data element)
These components always appear in this order. Not all components
are present in all data elements but the components that are
present maintain this relative order.
4.2.1 Identifier Octets
The identifier octet is a numeric code containing
information that identifies a data element. It is always the
first component in a data element. The Identifier octet contains
a one-bit flag, indicating whether or not the data element
contains a Property-List, and a seven-bit unique identifier for
the data element. The value of the data element identifier also
indicates whether the data element has a Qualifier. (See Table
2.)
32
Section 4.2.1
Bit Value Meaning
7 0 The data element does not have properties
associated.
1 The data element has properties associated.
6 0 The data element does not have a Qualifier.
1 The data element has a Qualifier.
TABLE 2. TYPE BITS IN THE IDENTIFIER OCTET
The most significant bit (Bit 7) of the identifier octet is
set to 1 if there are properties associated with the data
element; it is set to 0 if there are none. This bit is
independent of the remaining seven bits in the identifier octet,
which are called the identifier, and provide unique
identification for data elements. The associated properties are
specified in a Property-List component.
The second most significant bit (Bit 6) of the identifier
octet (the most significant bit of the identifier itself)
signifies whether or not the data element has a Qualifier. If
the bit is set to 1, then the data element has a Qualifier; if it
is a 0, the data element does not have a Qualifier. The seven
bits of the identifier uniquely identify the data element. (See
Figure 4.)
Data elements all have a Length Code component immediately
following the identifier octet. (See 4.2.2.1.)
4.2.2 Length code and Qualifier components
The Length Code and the Qualifier are both usually one octet
in length. They use an encoding scheme that permits extending
the component to the size necessary to represent the length of
the data element or the value of the Qualifier component.
The most significant bit of the Length Code or Qualifier
components determines whether it is one or several octets in
length. When the most significant bit is 0, the component is one
octet in length. When the most significant bit is 1, the other
seven bits of the first octet encode the number of octets in the
rest of the component. The actual value begins in the next octet
and is interpreted as an unsigned integer.
A single octet is sufficient for most Length Code and
Qualifier components. For those cases where the value of the
Length Code or the Qualifier must be greater than 127, extra
octets can be added, up to a maximum of 127 octets. Figure 5
shows the encoding scheme, as well as an example of a value less
than 127 and one greater than 127.
In order to comply with this message format specification,
CBMSs must be able to determine the value of any length code or
qualifier that is expressed in three octets or less. (The
16
2 -1). This message format specification places no limitation
on the value of a length code or qualifier generated by a CBMS
(except for the absolute limitation inherent in the
representation scheme). However, the use of length codes and
32
2 -1) should be avoided unless it is known that the receiving
system can handle them.
Both Length Codes and Qualifiers have a special convention
for dealing with special situations. Length Codes can specify
that a data element had indeterminate length; a Qualifier can
specify that a data element is implementation defined. These
cases are explained further in Sections 4.2.2.1 and 4.2.2.2.
bit 7 6 5 4 3 2 1 0
+---------------+
|0 x x x x x x x| xxxxxxx is the value.
+---------------+
+---------------+------//-------+
|1 n n n n n n n|y y y y y y y y| nnnnnnn is the
+---------------+------//-------+ number of octets
that contain the
value yyyyyyyy.
+---------------+
|0 0 0 0 1 0 0 1| This is an example with a
+---------------+ value of 9 (decimal).
+---------------+---------------+
|1 0 0 0 0 0 0 1|1 0 0 0 0 0 1 0| This example has a
+---------------+---------------+ value of 130 decimal.
FIG. 5. ENCODING MECHANISM FOR QUALIFIERS AND LENGTH CODES
The Length Code indicates the number of octets following it
in a data element (that is, excluding the identifier octet and
the length code itself). Length Codes appear in one of three
formats, short, long, and indefinite.
A short Length Code is one octet long. Its most significant
bit (Bit 7) is set to 0 and its value is in the range 0 through
127.
A long Length Code is at least two octets long. The first
octet always has its most significant bit (Bit 7) set to 1. The
other seven bits of this octet contain the number of octets
making up the rest of the Length Code and these octets contain
1016
(2 - 1) (that is, 127 octets to represent the value).
An indefinite Length Code is one octet long. Its most
significant bit (Bit 7) is set to 1 and its other bits are all 0.
(See Figure 6.) An indefinite Length Code may appear only as
bit 7 6 5 4 3 2 1 0
+---------------+
|0 x x x x x x x| xxxxxxx is the value of the
+---------------+ length code.
+---------------+------//-------+
|1 n n n n n n n|y y y y y y y y| nnnnnnn is the number
+---------------+------//-------+ of octets that contain
the value of the length
code; these are represented
as yyyyyyy.
+---------------+
|1 0 0 0 0 0 0 0| The "indefinite" length code
+---------------+
part of a constructor data element; it may not occur in a
4
primitive data element . A constructor data element with an
indefinite length code has an End-Of-Constructor data element as
the last data element in its Data Element Contents. (The length
of such a constructor data element is unrestricted although it
must contain at least one data element -- the End-of-Constructor
that terminates it -- in its Data Element Contents.)
Figure 7 shows the Length Codes for three elements; their
values are 38, 201, and 300.
4.2.2.2 Qualifier
The Qualifier component of a data element is used to provide
information essential to the interpretation of the data element
contents that is beyond that encoded in the identifier octet or
length code. For example, the identifier octet could contain the
_______________
4
This is the result of most primitive elements being able to
contain any bit pattern (including the identifier for End-Of-
Constructor).
code for a field and the Qualifier component would specify what
kind of field.
The Qualifier component appears in only a few data elements.
In the Bit-String data element, it indicates the number of unused
bits in the final octet of the Data Element Contents. In the
Field and Property data elements, it indicates which field or
property the data element represents. In the Compressed and
Encrypted data elements, it indicates which compression or
encryption algorithm has been used. In the Message data element,
it indicates the type of message.
In the sequence of data element components, the Qualifier
occurs between the Length Code and the Property-List components.
The length of the Qualifier component depends on the encoding of
the Qualifier. (See Figure 8.) A short Qualifier is one octet
long. Its most significant bit is 0 and its value is in the
range 0 through 127. A long Qualifier is at least two octets in
length. The most significant bit is always 1 and the other 7
bits indicate the number of octets in the value of the Qualifier.
This message format specification allows implementations to
define their own values for Qualifiers. A vendor-defined
Qualifier is any long Qualifier in which the first octet in the
value is 0. The value used to identify this Qualifier is not
guaranteed to be unique and the same value may be used by
different implementations to define different Qualifiers.
+--------+
|00011011| Qualifier with value 28 (decimal).
+--------+
+--------+--------+--------+
|10000010|00000001 00001010| Qualifier with value
+--------+--------+--------+ 266 (decimal).
+--------+--------+--------+--------+
|10000011|00000000|00000001 00001010| Vendor-Defined
+--------+--------+--------+--------+ Qualifier with
value 266.
+--------+
|10000000| Undefined value for a Qualifier.
+--------+
A Property is an attribute being associated with a data
element. The properties currently defined by this message format
specification are Printing-Name and Comment. A Property-List
component of a data element is represented by a Property-List
data element that in turn contains Property data elements.
A data element contains at most one Property-List. The most
significant bit in the identifier octet of the data element
indicates whether a Property-List is present. (See Section
4.2.1.)
4.2.4 Data Element Contents
The Data Element Contents component of a data element is the
actual data or information represented by a data element. (The
other components provide the information necessary to identify
and interpret the Data Element Contents.)
38
Section 4.2.4
In a primitive data element, the Data Element Contents is a
series of octets interpreted according to the identifier octet
and any qualifier.
In a constructor data element, the Data Element Contents is
a series of data elements. When the Length Code component of a
constructor data element is "indefinite", the last data element
in the constructor's Data Element Contents is End-of-Constructor.
The length of the Data Element Contents (in octets) is the
difference between the value of the Length Code and the sum of
the following:
o the length of the Qualifier component (depends on the
data element)
o the length of the Property-List component
4.3 Data Element Syntax
This message format specification defines nineteen (19)
different data elements. Section 4.3.1 defines the encoding form
for data elements in general and the syntax for each data
element. Section 4.3.2 describes the use of specific data
elements as part of the Data Element Contents of a Field data
element. A summary of the syntactic form appears in Appendix F;
summaries of the data element syntax appear in Appendix G.
4.3.1 Data elements
This section presents the general syntactic form for all
data elements defined by this message format specification and
the detailed syntax for each data element. The data elements are
presented by syntactic class: primitive data elements (Section
4.3.1.1), and constructors (Section 4.3.1.2).
For convenience, the following terminology is used in this
section.
39
Section 4.3.1
Term Meaning
Primitive a Primitive Data Element
Constructor a Constructor Data Element
Element any Data Element
The syntax of each Element is presented in graphic form.
The following conventions apply in the diagrams. A single octet
is represented as follows.
+--------+
| |
+--------+
Components that vary in length are represented as follows.
+---//---+
| |
+---//---+
Each Element has up to five components: an Identifier, a
Length Code, a Qualifier, a Property-List and the Data Element
Contents. (See Section 4.2.)
In the diagrams, the contents of the identifier octet is
shown as a "P" followed by an identifier represented in binary.
(See Figure 4.) The identifier itself is a seven bit quantity,
right justified in the identifier octet. Full details on
identifier octets appear in Section 4.2.1.
A length code is always represented in the following manner:
+---//---+
|Lxxxxxxx|
+---//---+
A qualifier is always represented in the following manner:
+---//---+
|Qxxxxxxx|
+---//---+
40
Section 4.3.1
A Property-List (if present) always immediately precedes any
occurrence of Data Element Contents.
The Data Element Contents appears in diagrams as one of the
following.
o "element(s)", which may be any data element(s)
o "anything", which is undefined and may be any
combination of bits
o a specific data element
o the interpretation to be applied to the bits within the
octets that constitute the element (such as ASCII or
Integer)
Two data elements have been reserved for special purposes.
The Extension data element is provided to allow for future
expansion of the possible data elements. The Vendor-Defined data
element allows CBMS vendors to define their own data elements.
Vendor-Defined data elements are not guaranteed to be unique,
since two implementations could define different data elements
using the same identifier. Vendor-Defined data elements should
be used and interpreted by prior agreement.
In the following sections, each element is presented with
its name, compliance classification (BASIC or OPTIONAL), its
identifier (both in hexadecimal and in octal), a brief
description of its use, and a graphic representation. Each data
element description has the following form.
41
Section 4.3.1
-----------------------------------------------------------------
Data Element (Compliance) identifier identifier
Name ( Category ) octet octet
16 8
Description of the syntax of the data element.
+---//---+
| | Diagram representing data element
+---//---+
The data elements in this section are arranged in
alphabetical order by name. (Appendix C presents the identifiers
in numeric order.)
ASCII-String (BASIC) 02 002
16 8
This data element contains a series of ASCII
characters, each character right-justified in one
octet. For seven-bit ASCII characters, the most
significant bit of each octet must be 0.
Bit-String (OPTIONAL) 43 103
16 8
This data element contains a series of bits. It uses
the Qualifier data element component to record the
number of bits of padding (as an eight bit unsigned
integer) needed to fill the final octet of the Data
Element Contents to an even octet boundary. These
padding bits have no meaning and occur in the low order
bits of the final octet. The valid values for the
Qualifier component are 0 through 7. The number of
bits in the Data Element Contents is calculated from
the following formula.
8 * number of octets - value of
in the Data Qualifier component
Element Contents
Boolean (OPTIONAL) 08 010
16 8
This data element contains one octet whose value is
either true or false. False is represented by all bits
being 0; true is represented by all bits being 1
(although any non-zero value should be interpreted as
true).
+--------+---//---+--------+
|P0001000|Lxxxxxxx| T or F |
+--------+---//---+--------+
End-of-Constructor (BASIC) 01 001
16 8
This data element terminates the Data Element Contents
in a constructor data element that has indefinite
length. This data element has no Contents component.
(Use of this element is described in Section 4.2.2.1.)
Integer (OPTIONAL) 20 040
16 8
This data element contains a 2's complement integer of
variable length, high order octet first. It is
recommended that the data element contents be either 2
or 4 octets long whenever possible.
No-Op (OPTIONAL) 00 000
16 8
This data element does nothing. No-Op is used whenever
it is necessary to include a data element that means
"no operation". It is a short placeholder.
Padding (OPTIONAL) 21 041
16 8
This data element is used to fill any number of octets.
The contents of a Padding element are undefined and
convey no information.
The data elements in this section are arranged in
alphabetical order.
44
Section 4.3.1.2
Compressed (OPTIONAL) 46 106
16 8
This data element must contain a Bit-String data
element. It is used to represent any data that has
been compressed; it may be used wherever its
uncompressed contents may appear. A Qualifier data
component appears in each Compressed data element; it
contains a compression identifier (CID) to identify
the compression algorithm used. (See Section 4.3.5.)
The Data Element Contents contains the product of the
compression process.
Date (BASIC) 28 050
16 8
This data element contains an ASCII-String data
element, which is a representation of a date and time
formatted in accordance with PUBS 4 [NatB-68],
58 [NatB-79a] and 59 [NatB-79b].
Encrypted (OPTIONAL) 47 107
16 8
This data element must contain a Bit-String. It is
used to represent any data that has been encrypted; it
may be used wherever its unencrypted contents may
appear. A Qualifier data component appears in each
Encrypted data element; it contains an encryption
identifier (EID) identifying the encryption algorithm
used. (See Section 4.3.4.) The Data Element Contents
is the product of the encryption process.
Extension (OPTIONAL) 7E 176
16 8
This data element is used to extend the number of
available data elements beyond the 128 that are
possible using a 7-bit identifier. A Qualifier
component extends the encoding space for identifiers.
(Extension and Vendor-Defined have the same syntax.)
Field (BASIC) 4C 114
16 8
This data element uses a Qualifier data element
component. The Qualifier component contains a Field
Identifier (FID) indicating which specific field is
being represented. (See Section 4.3.2.)
Message (BASIC) 4D 115
16 8
This data element may contain Field or Message data
elements. Its Qualifier component contains a Message
type (MID) indicating the type of the message. (See
Section 4.3.6.) (The MID is completely different from
the message identifier in the Message-ID field and
should not be confused with it.)
+--------//---------//---------//---------//--------+
| Field, Message, Encrypted, or Compressed Elements |
+--------//---------//---------//---------//--------+
46
Section 4.3.1.2
Property-List (OPTIONAL) 24 044
16 8
This data element contains a series of Property data
elements to be associated another data element.
Property (OPTIONAL) 45 105
16 8
This data element uses a Quali data element
component. The Qualifier component contains
a Property-Identifier (PID) to indicate which specific
property is being represented. (See Section 4.3.3.)
Sequence (OPTIONAL) 0A 012
16 8
This data element contains any series of data elements.
Sequence differs from Set in that the data elements
making up the Data Element Contents must be considered
as an ordered sequence (according to their order of
appearance in the sequence.)
Set (OPTIONAL) 0B 013
16 8
This data element contains any series of data elements
with no ordering of the elements implied. (Sequence
provides an ordered series.) Although the data
elements contained in a Set must be stored
sequentially, the order in which they are stored is not
defined and not processed.
Unique-ID (OPTIONAL) 09 011
16 8
This data element is a unique identifier. It need not
be human-readable. The Data Element Contents may be an
ASCII-String, a Bit-String, or an Integer.
Vendor-Defined (OPTIONAL) 7F 177
16 8
This data element is used to represent vendor- and
user-defined data elements. A Qualifier component
extends the encoding space for identifiers. The
Qualifier component is not guaranteed to be unique
among all interconnected systems. This data element is
interpreted according to prior agreement between
systems. (Extension and Vendor-Defined data elements
have the same syntax.)
The Data Element Contents of a particular field in a message
must contain at least one data element. The types of data
elements that can appear in the Data Element Contents of a field
are restricted according to what kind of field it is. Appendix A
(the master reference appendix for fields) nes which data
elements are valid as the Contents for each of the fields.
Some fields have a Data Element Contents that contains
"originators" or "recipients." No data element represents the
identities of originators or recipients (because that encoding is
not within the scope of this message format specification.)
These descriptions simply list "originators" or "recipients",
implying no restrictions on how the identifiers for originators
or recipients are represented.
48
Section 4.3.3
4.3.3 Properties and associated elements
This message format specification defines two properties.
Comment 01 001
16 8
This property may contain any series of data elements;
it most commonly contains one or more ASCII-Strings.
Printing-Name 02 002
16 8
This property contains one ASCII-String. In this case,
the ASCII-String may contain only the printing ASCII
characters plus the "space" character.
4.3.4 Encryption identifiers
This message format specification defines two encryption
identification codes.
Unspecified 00 000
16 8
Use of this encryption identifier as part of the
Encrypted data element indicates that the encryption
method being used was not specified for inclusion as
part of the data element.
NBS-Standard 01 001
16 8
Use of this encryption identifier as part of the
Encrypted data element indicates that the NBS standard
method for data encryption [NatB-77] was used.
4.3.5 Compression identifiers
This message format specification defines two compression
identification codes for use with the Compressed data element.
Unspecified 00 000
16 8
Use of this compression identifier as part of the
Compressed data element indicates that the compression
method being used was not specified for inclusion as
part of the data element.
NBS-Standard 01 001
16 8
Use of this compression identifier as part of the
Compressed data element is reserved at the present
time. It will be used in the future to indicate that
the NBS standard method for data compression was used
once the data compression standard is defined.
49
Section 4.3.6
4.3.6 Message types
This message format specification defines message type (MID)
codes for use in classifying the type of a message. The message
type could be confused with the message identifier in the
Message-Id field; they are completely distinct concepts.
NBS-Standard 01 01
16 8
This message type marks messages defined by this
message format specification.
50
SUMMARY OF APPENDIXES
Appendix A Defines the fields in the message format
specification. This alphabetical appendix is for
reference use by implementors. It contains semantic
definitions of fields from Section 3.1. It also
defines Field Identifier values and specifies which
data elements are valid as the Contents for each of
the fields.
Appendix B Defines the data elements in the message format
specification. This alphabetically ordered appendix
is for reference use by implementors. It
consolidates information from Section 4.3.
Appendix C Provides a reference table listing the data elements
in numerical order by their identifier octets.
Appendix D Provides a reference table summarizing the components
of messages according to whether they are required or
otional for CBMSs implementing the specification.
Appendix E Provides a reference table organizing the message
components according to the functional class of the
components.
Appendix F Provides an overview of the syntactic elements
defined by this message format specification.
Appendix G Summarizes syntactic elements according to whether
they are required or optional for a CBMS implementing
the message format specification.
Appendix H Examples of each syntactic element displaying their
syntax and describing their associated semantics.
51
Appendix A
APPENDIX A
FIELDS -- IMPLEMENTORS' MASTER REFERENCE
This appendix defines all of the fields in the message
format specification for reference use by implementors. It
contains semantics definitions of fields from Section 3.1. It
also defines Field Identifier values and which data elements are
valid as the Contents for each of the fields. The field
definitions appear alphabetically.
Each field in the list has the following form:
-----------------------------------------------------------------
Field Name Compliance identifier identifier
value value
16 8
Description of the field semantics. Names of
data elements that are valid in the Data Element
Contents of this kind of field.
Attachments OPTIONAL 08 010
16 8
This field contains additional data accompanying a
message. It is similar in intent to enclosures in a
conventional mail system. Contents of this field are
unrestricted.
Author OPTIONAL 0C 014
16 8
This field identifies the individual(s) who wrote the
primary contents of the message. Use of the Author
field is discouraged when the contents of the Author
field and the From field would be completely redundant.
This field contains one or more originator identities.
Bcc OPTIONAL 0D 015
16 8
This field identifies additional recipients for a
message (a "blind carbon copies list"). The contents
of this field are not to be included in copies of the
message sent to the primary and secondary recipients.
See section 3.2.1 for further discussion of the use of
blind carbon copies lists. This field contains one or
more recipient identities.
52
Appendix A
Cc BASIC 06 006
16 8
This field identifies secondary recipients for a
message (a "carbon copies" list). This field contains
one or more recipient identities.
Circulate-Next OPTIONAL 0E 016
16 8
This field is used in conjunction with the Circulate-To
field. (See Section 3.2.6.1.) It identifies all
recipients in a circulation list who have not yet
received the message. This field contains one or more
recipient identities.
Circulate-To OPTIONAL 0F 017
16 8
This field identifies recipients for a circulated
message. (See Section 3.2.6.1.) It is used in
conjunction with the Circulate-Next field. This field
contains one or more recipient identities.
Comments OPTIONAL 10 020
16 8
This field permits adding comments onto the message
without disturbing the original contents of the
message. While the Comments field will usually contain
one or more ASCII-Strings, there are no restrictions on
its contents.
Date OPTIONAL 11 021
16 8
This field contains a date that the message's
originator wishes to associate with a message. The
Date field is to the Posted-Date field as the date on a
letter is to the postmark added by the post office.
This field contains one Date.
End-Date OPTIONAL 12 022
16 8
This field contains the date on which a message loses
effect. (See also Section 3.2.5.) This field contains
one Date.
From REQUIRED 01 001
16 8
This field contains the identity of the originators
taking formal responsibility for this message. The
contents of the From field is to be used for replies
when no Reply-to field appears in a message. This
field contains one or more originator identities.
In-Reply-To OPTIONAL 13 023
16 8
This field designates previous correspondence to which
this message is a reply. The usual contents of this
field would be the contents of the Message-ID field of
the message(s) being replied to. This field contains
one or more Unique-IDs or ASCII-Strings.
53
Appendix A
Keywords OPTIONAL 14 024
16 8
This field contains keywords or phrases for use in
retrieving a message. This field contains one or more
ASCII-Strings. (Each keyword or phrase is represented
by a separate ASCII-String.)
Message-Class OPTIONAL 15 025
16 8
This field indicates the purpose of a message. For
example, it might contain values indicating that the
message is a memorandum or a data-base entry. This
field contains one data element, an ASCII-String.
Message-ID OPTIONAL 16 026
16 8
This field contains a unique identifier for a message.
This identifier is intended for machine generation and
processing. Further definition appears in Section
3.2.4.1. Only one Message-ID field is permitted in a
message. This field contains one data element, a
Unique-ID.
Obsoletes OPTIONAL 26 046
16 8
This field identifies one or more messages that this
one supplants. This field contains at least one
Unique-ID and may contain more than one.
Originator-Serial-Number OPTIONAL 17 027
16 8
This field contains one or more serial numbers assigned
by the message's originator. (Messages with multiple
recipients should all have the same value in the
Originator-Serial-Number field. This field contains
one or more ASCII-Strings. (One ASCII-String is used
for each serial number.)
Posted-Date REQUIRED 02 002
16 8
This field contains the posting date, which is the
point in time when the message passes through the
posting slot into a message transfer system. Only one
Posted-Date field is permitted in a message. This
field contains one Date.
Precedence OPTIONAL 18 030
16 8
Ordinarily, message precedence or priority is a service
request to a message transfer system. A message
originator, however, can include precedence information
in a message. This field indicates the precedence at
which the message was posted. One example of a
precedence scheme is the US Military categories
"ROUTINE", "PRIORITY", "IMMEDIATE", "FLASH OVERRIDE",
and "EMERGENCY COMMAND PRECEDENCE". This field
contains one ASCII-String.
54
Appendix A
Received-Date OPTIONAL 19 031
16 8
Delivery date. This field may be added to a message by
the recipient's message receiving program. It
indicates when the message left the delivery system and
entered the recipient's message processing domain.
This field contains one Date.
Received-From OPTIONAL 1A 032
16 8
This field contains a record of a message's path
through a message transfer system. The
recipient's message receiving program may store any
such information that it obtains from a message
transfer system in this field. The contents of this
field are unrestricted.
References OPTIONAL 20 040
16 8
This field identifies other correspondence that this
message references. If the other correspondence
contains a Message-ID field, the contents of the
References field must be the message identifier. This
field contains one or more Unique-IDs or ASCII-Strings.
Reissue-Type OPTIONAL 25 045
16 8
This field is used in conjunction with message
encapsulating (see Section 3.2.2) to differentiate
between messages being assigned or redistributed. This
field contains one data element, usually an ASCII-
String.
Reply-To BASIC 03 003
16 8
This field identifies any recipients for replies to the
message. This field contains one or more recipient
identities.
Sender OPTIONAL 22 042
16 8
This field identifies the agent who sent the message.
It is intended either for when the sender is not the
originator responsible for the message or to indicate
who among a group of originators responsible for the
message actually sent it. Use of the Sender field is
discouraged when the contents of the Sender field and
From field would be completely redundant. Only one
Sender field is permitted in a message. This field
contains one originator identity.
Start-Date OPTIONAL 23 043
16 8
This field contains the date on which a message takes
effect. (See also Section 3.2.5.) This field contains
one Date.
55
Appendix A
Subject BASIC 07 007
16 8
This field contains whatever information the originator
provided to summarize or indicate the nature of the
message. This field contains one or more ASCII-
Strings.
Text BASIC 04 004
16 8
This field contains the primary content of the message.
Contents of this field are unrestricted.
To REQUIRED 05 005
16 8
This field identifies primary recipients for a message.
This field contains one or more recipient identities.
Warning-Date OPTIONAL 24 044
16 8
This field is used either alone or in conjunction with
an End-Date field. It contains one or more dates.
These dates could be used by a message processing
program as warnings of an impending end-date or other
event. (See also Section 3.2.5.) This field contains
one or more Dates.
56
Appendix B
APPENDIX B
DATA ELEMENTS -- IMPLEMENTORS' MASTER REFERENCE
The appendix defines all of the data elements in the message
format specification, for reference use by implementors. It
contains no new information but rather consolidates the syntactic
information from Section 4.3.
Each data element description has the following form.
This data element contains a series of ASCII
characters, each character right-justified in one
octet. For seven-bit ASCII characters, the most
significant bit of each octet must be 0.
This data element contains a series of bits. It uses
the Qualifier data element component to record the
number of bits of padding (as an eight bit unsigned
integer) needed to fill the final octet of the Data
Element Contents to an even octet boundary. These
padding bits have no meaning and occur in the low order
bits of the final octet. The valid values for the
Qualifier component are 0 through 7. The number of
bits in the Data Element Contents is calculated from
the following formula.
8 * number of octets - value of
in the Data Qualifier component
Element Contents
This data element contains one octet whose value is
either true or false. False is represented by all bits
being 0; true is represented by all bits being 1
(although any non-zero value should be interpreted as
true).
+--------+---//---+--------+
|P0001000|Lxxxxxxx| T or F |
+--------+---//---+--------+
58
Appendix B
Compressed (OPTIONAL) 46 106
16 8
constructor
This data element must contain a Bit-String data
element. It is used to represent any data that has
been compressed; it may be used wherever its
uncompressed contents may appear. A Qualifier data
component appears in each Compressed data element; it
contains a compression identifier (CID) to identify the
compression algorithm used. (See Section 4.3.5.) The
Data Element Contents contains the product of the
compression process.
This data element contains an ASCII-String data
element, which is a representation of a date and time
formatted in accordance with FIPS Publications 4 [NatB-
68], 59 [NatB-79b], and 58 [NatB-79a].
This data element must contain a Bit-String. It is
used to represent any data that has been encrypted; it
may be used wherever its unencrypted contents may
appear. A Qualifier data component appears in each
Encrypted data element; it contains an encryption
identifier (EID) identifying the encryption algorithm
used. (See Section 4.3.4.) The Data Element Contents
is the product of the encryption process.
This data element terminates the Data Element Contents
in a constructor data element that has indefinite
length. This data element has no Contents component.
(Use of this element is described in Section 4.2.2.1.)
This data element is used to extend the number of
available data elements beyond the 128 that are
possible using a 7-bit identifier. A Qualifier
component extends the encoding space for identifiers.
(Extension and Vendor-Defined have the same syntax.)
This data element uses a Qualifier data element
component. The Qualifier component contains a Field
Identifier (FID) indicating which specific field is
being represented. (See Section 4.3.2.)
This data element contains a 2's complement integer of
variable length, high order octet first. It is
recommended that the data element contents be either 2
or 4 octets long whenever possible.
This data element may contain Field or Message data
elements. Its Qualifier component contains a Message
type (MID) indicating the type of the message. (See
Section 4.3.6.) (The MID is completely different from
the message identifier in the Message-ID field and
should not be confused with it.)
+--------//---------//---------//---------//--------+
| Field, Message, Encrypted, or Compressed Elements |
+--------//---------//---------//---------//--------+
61
Appendix B
No-Op (OPTIONAL) 00 000
16 8
primitive
This data element does nothing. No-Op is used whenever
it is necessary to include a data element that means
"no operation". It is a short placeholder.
This data element uses a Qualifier data element
component. The Qualifier component contains
a Property-Identifier (PID) to indicate which specific
property is being represented. (See Section 4.3.3.)
This data element contains any series of data elements.
Sequence differs from Set in that the data elements
making up the Data Element Contents must be considered
as an ordered sequence (according to their order of
appearance in the sequence.)
This data element contains any series of data elements
with no ordering of the elements implied. (Sequence
provides an ordered series.) Although the data
elements contained in a Set must be stored
sequentially, the order in which they are stored is not
defined and not processed.
This data element is a unique identifier. It need not
be human-readable. The Data Element Contents may be an
ASCII-String, a Bit-String, or an Integer.
This data element is used to represent vendor-defined
data elements. A Qualifier component extends the
encoding space for identifiers. The Qualifier
component is not guaranteed to be unique among all
interconnected ems. This data element is
interpreted according to prior agreement between
systems. (Extension and Vendor-Defined data elements
have the same syntax.)
APPENDIX D
SUMMARY OF MESSAGE FIELDS BY COMPLIANCE CATEGORY
This appendix is for reference use. It contains no new
information, but rather abstracts from that presented in Section
3.1.
This appendix contains the message field names arranged
alphabetically within compliance category. (Appendix E orders
the field names within functional category.) Complete field
definitions appear in Appendix A.
Required fields must appear in a message. Basic fields must
be recognized and processed by all CBM systems. Optional fields
need not be supported by a CBMS but, if supported, must be
processed according to the meanings defined by the message format
specification.
APPENDIX E
SUMMARY OF MESSAGE SEMANTICS BY FUNCTION
This appendix is for reference use. It contains no new
information, but rather abstracts from that presented in Section
3.1.
This appendix contains the message field names arranged
alphabetically within functional class. (Appen orders the
field names within compliance class.) Complete field definitions
appear in Appendix A.
Attachments
Comments
Keywords
Message-Class
Precedence
Subject
Text
E.6 Reply Generation
Reply-To
E.7 Reissuing
Reissue-Type
E.8 Sending (Normal Transmission)
Author
Bcc
Cc
Date
From
Posted-Date
Sender
To
69
Appendix F
APPENDIX F
SUMMARY OF DATA ELEMENT SYNTAX
This appendix summarizes data element syntax by diagramming
the components of data elements. Detailed presentation of data
element syntax appears in Section 4.3.1.
In these diagrams, required components of a data element
appear as follows. (The double border signifies "required".)
+========+ +===//===+
| | | |
+========+ +===//===+
always one one or more
octet long octets long
Optional components of data elements are represented as
follows. (The single border signifies "not required".)
+--------+ +---//---+
| | | |
+--------+ +---//---+
always one one or more
octet long octets long
The first octet in a data element is the identifier octet.
In diagrams of data elements, all eight bits of the identifier
octet are always shown. Bits with fixed values show the fixed
values as 1s and 0s. Bits with variable values are shown as x's
and y's.
The first bit in an identifier octet is the P-bit. Its
value indicates whether a data element contains a property list.
(A P-bit value of 1 indicates the presence of a property list.)
The remaining seven bits contain the rest of the identifier.
Other octets in a data element belong to one of four
classes, Length Code, Qualifier, Property-List, and Contents. In
diagrams of syntax the data element components are labeled
according to their class.
70
Appendix F
Component Class Label
Length code Length
Qualifier Qual
Property-List P-List
Contents Contents
Data elements must follow this form.
+========+===//===+---//---+---//---+---//---+
|Pxxxxxxx| Length | Qual | P-List |contents|
+========+===//===+---//---+---//---+---//---+
The value of the Length component is the total number of octets
following the length code octet in the data element.
71
Appendix G
APPENDIX G
SUMMARY OF DATA ELEMENTS BY COMPLIANCE CATEGORY
Compliance categories for syntactic elements are basic and
optional. Every CBMS is required to recognize and process basic
elements. A CBMS is not required to process optional elements
although many are strongly recommended by the semantics.
This appendix summarizes data elements by listing them
according to their compliance category.
This appendix presents at least one example for each of the
data elements defined in this message format specification. In
these examples, identifier octets are represented in binary form.
All other numbers are presented in hexadecimal. ASCII strings
are shown as characters rather than their numerical
representation. Although this message format specification does
not define the syntax of names and addresses, message originators
and recipients are identified by their names. This does not
imply anything about how naming and addressing can or should be
done; it is simply a convenient way to identify message
originators and recipients in these examples.
H.1 Primitive Data Elements
This section contains an example of each of the primitive
data elements. Each example contains a short explanation and a
series of octets.
No-Op data element:
Bit-String data element containing 44 bits of data (((7-1) x
8) - 4). Six octets are used to hold those 44 bits. The last 4
bits in the final octet are padding and are therefore ignored.
Bit-String Length Spare
+--------+--------+--------+--------+--------+
|01000011| 0 7 | 0 4 | 0 A 3 B
+--------+--------+--------+--------+--------+
+--------+--------+--------+--------+
5 F 2 9 1 C D 0 |
+--------+--------+--------+--------+
H.2 Constructor Data Elements
This section contains an example of each of the constructor
data elements. Each example contains a short explanation and
then an annotated series of the data elements making up the
constructor.
Property-List data element containing one Property data
element. The property is Printing-Name and its value is
"Distribution":
ASCII Length
+--------+--------+---- ----+
|00000010| 0 C |Distribution|
+--------+--------+---- ----+
76
Appendix H
Printing-Name Property. The value of the Printing-Name is
"Distribution":
Property Length PID ASCII Length
+--------+--------+--------+--------+--------+
|01000101| 0 F | 0 2 |00000010| 0 C |
+--------+--------+--------+--------+--------+
+---- ----+
|Distribution|
+---- ----+
Compressed data element. Its contents were compressed using
an as-yet-undefined NBS standard data compression algorithm. The
compressed data is in a bit-string that is 56 bits long, fully
filling 7 octets:
Spare
+--------+--------+--------+--------+
| 0 0 | 1 C 5 F 2 D
+--------+--------+--------+--------+
+--------+--------+--------+--------+
7 7 B A F 6 2 9 |
+--------+--------+--------+--------+
77
Appendix H
Encrypted data element. The encryption method used to
encrypt its contents has been intentionally not specified. This
element contains a Bit-String which contains 22 bits (((4-1) x 8)
- 2) of data. These 22 bits are represented in octets; the final
2 bits in the final octet are padding and are therefore ignored:
Set data element containing two Integer data elements. The
first integer has a value of 519 (decimal) while the value of the
second is 71 (decimal). (These two value have no ordering
because they belong to a set.)
Field data element. The specific field shown is the Text
field with the contents "I will see you at lunch.":
Field Length FID ASCII Length
+--------+--------+--------+--------+--------+
|01001100| 1 B | 0 4 |00000010| 1 8 |
+--------+--------+--------+--------+--------+
+---- ----+
|I will see you at lunch.|
+---- ----+
79
Appendix H
Message containing four fields, Posted-Date, From, Text, and
To. It was sent on July 4, 1980 at 6 p.m. eastern daylight time.
It is from a person named Smith. The text of the message is a
question asking the recipient "Are you going to watch the
fireworks?". The message is sent to Jones:
Message Length Type Field Length
+--------+--------+--------+--------+--------+
|01001101| 5 8 | 0 1 |01001100| 1 7 |
+--------+--------+--------+--------+--------+
Extension data element containing a length code and 3
octets. The octet immediately following the length code
identifies it as Extension Data Element 7. The Data Element
Contents is the final two octets. The interpretation of the Data
Element Contents would be defined in an extension or successor to
this message format specification. [Note: this is an example.
Any actual extension data element 7 (if it were ever used) would
be completely different from anything done here.]:
Extension Length
+--------+--------+--------+--------+--------+
|01111110| 0 3 | 0 7 | 4 A E 9 |
+--------+--------+--------+--------+--------+
Vendor-Defined data element containing a length code and 3
octets. The first octet identifies this as vendor-defined data
element number 114 (decimal), which this particular vendor has
defined to contain three printable ASCII characters in two
octets. (Data element 114 (decimal) for another user would be
completely different. For example, it might contain a floating
point number.):
User Length
+--------+--------+--------+--------+--------+
|01111111| 0 3 | 7 2 | P O E |
+--------+--------+--------+--------+--------+
H.3 Fields
This section contains examples of Field data element
constructors for each several different fields (Keywords, Text,
Subject, Vendor-Defined).
81
Appendix H
Field data element for keywords . The field contains two
keywords, Message and Computer, each represented in a separate
ASCII-string data element.
Field data element for Text with a Property-List data
element containing a comment attached. The text field contains
the ASCII-String data element "Do you want lunch?"; the Property-
List data element contains a comment property, which consists of
an ASCII-string data element containing "Now?":
Field Length Text Prop-List Length
+--------+--------+--------+--------+--------+
|11001100| 2 0 | 0 4 |00100100| 0 9 |
+--------+--------+--------+--------+--------+
Field data element for Subject containing an ASCII-String
data element ("Good restaurants in Detroit" followed by a
carriage return and a line feed). (A recipient would expect the
message to contain some information about restaurants in the
Detroit area.):
Field Length Subject ASCII Length
+--------+--------+--------+--------+--------+
|01001100| 2 1 | 0 7 |00000010| 1 E |
+--------+--------+--------+--------+--------+
+---- ----+
|Good restaurants in Detroit.<cr><lf>|
+---- ----+
83
Appendix H
Field data element whose form and meaning was defined by a
vendor. This vendor has defined vendor-defined field 12
(decimal) to be a field with a printing name of "Reply-by" and
contents consisting of a date; January 7, 1981 in this case.
(The meaning of vendor-defined field 12 is unique to the vendor;
the same field number would have different meaning for other
vendors.):
Field Length Qualifier User number
+--------+--------+--------+--------+--------+
|11001100| 1 F | 8 2 | 0 0 0 C |
+--------+--------+--------+--------+--------+
Prop-List Length Property Length
+--------+--------+--------+--------+
|00100100| 0 E |01000101| 0 C |
+--------+--------+--------+--------+
Date Length ASCII Length
+--------+--------+--------+--------+
|00101000| 0 A |00000010| 0 8 |
+--------+--------+--------+--------+
+--- ---+
|19810107|
+--- ---+
H.4 Messages
This section contains several examples of complete messages
and shows the results of reissuing a message. (See Section
3.2.2.)
84
Appendix H
The following sample message had Stevens as its originator
and Johnson as its recipient. The message was sent on August 14,
1980 at 10 am EDT. The subject of the message is "Project
Deadline" and the message is a reminder that the deadline is the
next day and that the section of the report for the project being
done by Johnson should be turned in to Stevens by 3 pm that day.
Message Length Type
+--------+--------+--------+--------+
|01001101| 8 1 | B 4 | 0 1 |
+--------+--------+--------+--------+
Field Length FID ASCII
+--------+--------+--------+--------+
|01001100| 0 A | 0 5 |00000010|
+--------+--------+--------+--------+
Field Length FID ASCII Length
+--------+--------+--------+--------+--------+
|01001100| 6 D | 0 4 |00000010| 6 A |
+--------+--------+--------+--------+--------+
+----
|Don't forget the project report is
+----
due tomorrow. Please have<CrLf>
your section to me by three this
----+
afternoon.|
----+
The following example illustrates the results of reissuing
the first message in this section. This message contains the
original message (as a Message data element), To, From, and
Posted-Date fields, and a Reissue-Type field with Redistributed
as its value:
Message Length Type
+--------+--------+--------+--------+
|01001101| 8 1 | F 8 | 0 1 |
+--------+--------+--------+--------+
Field Length FID ASCII Length
+--------+--------+--------+--------+--------+
|01001100| 6 D | 0 4 |00000010| 6 A |
+--------+--------+--------+--------+--------+
+----
|Don't forget the project report is
+----
due tomorrow. Please have<CrLf>
your section to me by three this
----+
afternoon.|
----+
H.5 Unknown Lengths
This section contains two examples of data elements with an
unknown length. The two examples have been presented in sections
H.2 and H.4, but with a known rather than an unknown length.
88
Appendix H
Set data element with an unknown length containing two
Integer data elements. The first integer has a value of 519
(decimal) while the value of the second is 71 (decimal). (These
two value have no ordering because they belong to a set.)
The following sample message with an unknown length had
Stevens as its originator and Johnson as its recipient. The
message was sent on August 14, 1980 at 10 am EDT. The subject of
the message is "Project Deadline" and the message is a reminder
that the deadline is the next day and that the section of the
report for the project being done by Johnson should be turned in
to Stevens by 3 pm that day.
[BlaR-80]
R. P. Blanc and J. F. Heafner. The NBS Program in Computer
Network Protocol Standards. In Proceedings, ICCC 80. 1980.
[CroD-77]
David H. Crocker, John J. Vittal, Kenneth T. Pogran,
D. Austin Henderson, Jr. Standard for the Format of ARPA
Network Text Messages. RFC 733, The Rand Corporation, Bolt
Beranek and Newman Inc, Massachussets Institute of
Technology, Bolt Beranek and Newman Inc., November, 1977.
[FeiE-79]
E. Feinler, J. Pickens, and A. Sjoberg. Computer Message
Services Bibliography. Technical Report NIC-BIBLIO-791201,
SRI International, December, 1979.
[ISOD-79]
ISO/TC97/SC6 Data Communications. Second Draft Proposed
Communication Heading Format Standard. ISO/TC97/SC6 N 1948,
ISO International Organization for Standardization
Organization Internationale de Normalisation, September,
1979. Secretariat: USA (ANSI).
[ISOD-81]
ISO/TC97/SC16. Open Systems Interconnection Basic Reference
Model. ISO/TC97/SC16 N, ISO International Ozation for
Standardization Organization Internationale de
Normalisation, 1981.
[NatB-68]
National Bureau of Standards. Calendar Date. Federal
Information Processing Standards Publication 4, U.S.
Department of Commerce / National Bureau of Standards,
November, 1968.
[NatB-77]
National Bureau of Standards. Data Encryption Standard.
Federal Information Processing Standards Publication 46,
U.S. Department of Commerce / National Bureau of Standards,
January, 1977.
[NatB-79a]
National Bureau of Standards. Representations of Local Time
of the Day for Information Interchange. Federal Information
Processing Standards Publication 58, U.S. Department of
Commerce / National Bureau of Standards, February, 1979.
92
[NatB-79b]
National Bureau of Standards. Representations of Universal
Time, Local Time Differentials, and United States Time Zone
References for Information Interchange. Federal Information
Processing Standards Publication 59, U.S. Department of
Commerce / National Bureau of Standards, February, 1979.
[PosJ-79]
Jonathan B. Postel. INTERNET MESSAGE PROTOCOL. RFC 753,
Information Sciences Institute, March, 1979.
[SchP-79]
Peter Schicker. The Computer Based Mail Environment: An
Overview. Technical Report, Bell-Northern Research Ltd.,
Ottawa, Ontario, Canada, December, 1979.
[TasG-80]
Task Group X3S33 on Data Communications Formats, ANSI
Subcommittee X3S3 on Data Communications. Third Draft
Proposed American National Standard for Heading Format
Structure for Code Independent Communication Headings. ANSI
document X3S37/80-01, Computer and Business Equipment
Manufacturers Association, 1980.
