Network Working Group H. Khartabil

Network Working Group H. Khartabil
Request for Comments: 4661 Telio
Category: Standards Track E. Leppanen
M. Lonnfors
J. Costa-Requena
Nokia
September 2006

An Extensible Markup Language (XML)-Based Format for
Event Notification Filtering

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2006).

Abstract

The SIP event notification framework describes the usage of the
Session Initiation Protocol (SIP) for subscriptions and notifications
of changes to a state of a resource. The document does not describe
a mechanism whereby filtering of event notification information can
be achieved. Filtering is a mechanism for defining the preferred
notification information to be delivered and for specifying triggers
that cause that information to be delivered. In order to enable
this, a format is needed to enable the subscriber to describe the
state changes of a resource that cause notifications to be sent to it
and what those notifications are to contain. This document presents
a format in the form of an XML document.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Structure of XML-Encoded Simple-Filter . . . . . . . . . . . . 4
3.1. MIME Type for Simple-Filter Document . . . . . . . . . . 4
3.2. The <filter-set> Root Element . . . . . . . . . . . . . 4
3.3. The <ns-bindings> Element . . . . . . . . . . . . . . . 4
3.4. The <filter> Element . . . . . . . . . . . . . . . . . . 5
3.5. The <what> Element . . . . . . . . . . . . . . . . . . . 6
3.5.1. The <include> Element . . . . . . . . . . . . . 6
3.5.2. The <exclude> Element . . . . . . . . . . . . . 7
3.5.3. The 'type' Attribute . . . . . . . . . . . . . . 7
3.6. The <trigger> Element . . . . . . . . . . . . . . . . . 8
3.6.1. The <changed> Element . . . . . . . . . . . . . 8
3.6.2. The <added> Element . . . . . . . . . . . . . . 9
3.6.3. The <removed> Element . . . . . . . . . . . . . 10
4. XML Schema Extensibility . . . . . . . . . . . . . . . . . . . 10
5. Syntax for Referencing XML Items and Making Logical
Expressions . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Filter Criteria Using <what> Element . . . . . . . . . . 12
6.2. Filter Criteria Using <trigger> Element . . . . . . . . 13
6.3. Filter Criteria Using <what> and <trigger> Elements . . 13
6.4. Content Filter Using Namespaces . . . . . . . . . . . . 14
6.5. Content Filter Using Only <include> Elements . . . . . . 14
6.6. Two Content Filters as Filter Criteria . . . . . . . . . 15
7. XML Schema for Filter Criteria . . . . . . . . . . . . . . . . 16
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9.1. application/simple-filter+xml MIME TYPE . . . . . . . . 19
9.2. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:simple-filter . . . . . . . . . . . 20
9.3. Schema Registration . . . . . . . . . . . . . . . . . . 20
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . 21

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1. Introduction

The SIP event notification framework [2] describes the usage of the
Session Initiation Protocol (SIP) for subscriptions and notifications
of changes to a state of a resource. The document does not describe
a mechanism whereby filtering of event notification information can
be achieved.

Filtering is a mechanism for defining the preferred notification
information, referred to as content, to be delivered and for
specifying the rules for when that information should be delivered.

The filtering mechanism is expected to be particularly valuable and
primarily applicable to users of mobile wireless access devices. The
characteristics of the devices typically include high latency, low
bandwidth, low data processing capabilities, small display, and
limited battery power. Such devices can benefit from the ability to
filter the amount of information generated at the source of the event
notification. However, implementers need to be aware of the
computational burden on the source of the event notification. This
is discussed further in Section 8.

The structure of the filter criteria is described using the XML
schema. The filter criteria is presented as an XML document. The
XML document contains the user's preference as to when notifications
are to be sent to it and what they are to contain. The scope of the
"when" part is triggering.

The triggering is defined as enabling a subscriber to specify
triggering rules for notifications where the criteria are based on
changes of the event package [2] specific state information, e.g.,
for the presence information document [15], the change in the value
of the <status> element.

The functionality of the filtering regarding the SIP event
notifications is specified in [3].

2. Conventions

In this document, the key words 'MUST', 'MUST NOT', 'REQUIRED',
'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY',
and 'OPTIONAL' are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant implementations.

Throughout the document, the "resulting XML document" refers to the
final XML document that carries state information to be delivered to
the subscriber after the filters have been applied to it.

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"Content" refers to the XML document that appears in a notification
reflecting the state of a resource.

3. Structure of XML-Encoded Simple-Filter

A simple-filter is an XML document [8] that MUST be well formed and
MUST be valid according to schemas, including extension schemas,
available to the validater, and applicable to the XML document. The
simple-filter documents MUST be based on XML 1.0 and MUST be encoded
using UTF-8.

The namespace identifier for elements defined by this specification
is a URN [5], which uses the namespace identifier 'ietf' defined by
[6] and extended by [4]. This urn is:
urn:ietf:params:xml:ns:simple-filter.

This namespace declaration indicates the namespace on which the
filter criteria are based.

3.1. MIME Type for Simple-Filter Document

The MIME type for the simple-filter document is "application/
simple-filter+xml". Any transport protocol (SIP [12], for example)
used to carry the filters that also carries payload type information
MUST identify the payload as MIME type
"application/simple-filter+xml" (for example, a Content-Type header
field).

3.2. The <filter-set> Root Element

The root element of the filter criteria is <filter-set>.

The <filter-set> element contains the namespace definition mentioned
above. With the optional 'package' attribute, it is possible to
define the package to which the filter criteria is applied. This
might be especially useful in cases where the XML document containing
the filter criteria is separated from the events that make use of it
or from the protocol that usually carries it.

The <filter-set> element may contain one <ns-bindings> element.

The <filter-set> element contains one or more <filter> elements.

3.3. The <ns-bindings> Element

The <ns-bindings> element is used to bind namespaces to local
prefixes used in expressions that select elements or attributes using

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the syntax in Section 5. Those prefixes apply to the <include>,
<exclude>, <changed>, <added>, and <removed> elements.

The <ns-bindings> element contains one or more <ns-binding> elements.
Each <ns-binding> element has a 'prefix' attribute. The value of the
'prefix' attribute is a prefix used to qualify the elements pointed
to by the expression. The <ns-binding> element also has a 'urn'
attribute that identifies the namespace that the prefix represents.

3.4. The <filter> Element

The <filter> element is used to specify the content of an individual
filter.

The <filter> element has an 'id' attribute. The value of the 'id'
attribute MUST be unique within the <filter-set> element. The
<filter> MAY have a 'uri' attribute. The value of the 'uri'
attribute is the URI of the resource to which the filter applies.
The <filter> MAY have a 'domain' attribute. The value of the
'domain' attribute is the domain of the resources to which the filter
applies. The 'uri' attribute and the 'domain' attribute MUST NOT
appear together in the <filter>.

The URI of the resource is useful in cases where the 'event list'
extension [17] is used with a package. Since a subscription to an
event package may be addressed to an event list, the 'uri' attribute
allows the subscriber to define a filter specific to an individual
resource within that list. That resource may be another list. The
'uri' attribute may, of course, carry the URI of the list itself. If
the <filter> does not contain the 'uri' attribute, the filter applies
to the resource identified in the subscription request.

The 'domain' attribute carries a domain. In this case, the filter
applies to resources whose URI has a domain part matching that
domain. This can be used when a subscription is for a resource that
is an event list with many resources from differing domains.

URI matching is done according to the matching rules defined for a
particular scheme. When matching domains, the user part of the URI
is ignored for matching purposes.

The <filter> MAY have a 'remove' attribute that together with the
'id' attribute indicates the existing filter to be removed. The
value of the 'remove' attribute is of the type "Boolean". The
default value is "false".

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The <filter> MAY have an 'enabled' attribute that indicates whether a
filter is enabled or disabled. The value of the 'enabled' attribute
is of the type "Boolean". The default value is "true".

The <filter> element MAY contain a <what> element and MAY contain one
or more <trigger> elements, but it MUST contain either the <what>
element or the <trigger> element when the filter is being enabled for
the first time. When a filter is disabled by setting the 'enabled'
attribute to "false", the <what> and <trigger> elements MAY be
omitted. Similarly, when a filter is re-enabled by setting the
'enabled' attribute to "true", the <what> and <trigger> elements MAY
be omitted.

Filter contents can be changed by changing the contents in the <what>
and <trigger> elements and maintaining the value of the filter 'id'
attribute.

3.5. The <what> Element

The <what> element is used to specify the content to be delivered to
the user. It does not specify the exact content but the rules that
are used to construct that information.

The <what> element may contain one or more <include> elements and one
or more <exclude> elements. When more than one <include> element has
been defined, the results are additive. That is, each <include>
element adds an element or attribute to the resulting XML document.
When more than one <exclude> element has been defined, each <exclude>
element value depletes the contents of the resulting XML document.

3.5.1. The <include> Element

The <include> element is used to select the content to be delivered.
Its value can identify an XML element, an attribute, or a namespace
of an XML document to be filtered. This is indicated using the
'type' attribute.

Note that the resulting XML document MUST be valid. Therefore, in
addition to including the elements identified with the <include>
element value, all other mandatory XML elements and/or attributes
must be incorporated in the resulting XML document in order to make
it valid. This, in practice, means that a subscriber defining a
filter only needs to <include> optional elements and/or attributes,
but may <include> mandatory elements and/or attributes as well.
There are also cases where a filter selects an attribute that belongs
to an optional element. In this case, the optional element needs to
appear in the resulting XML document.

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The syntax defined in Section 5 (see the definition of "selection")
MUST be used. The following example selects the <basic> element
defined in the PIDF [13]. This results in the selection of the
<basic> element as well as all the ancestors, i.e., <status> and
<tuple>.

<include type="xpath">/presence/tuple/status/basic</include>.

3.5.2. The <exclude> Element

The <exclude> element is used to define exceptions to the set of XML
elements and/or attributes selected by the <include> elements. Thus,
XML elements (including their lower-level "child" elements) and/or
attributes defined by the <exclude> element are not delivered. This
is most useful when an <include> element identifies a namespace.

The <exclude> element has the optional 'type' attribute (see the
definition of the 'type' in Section 3.5.3).

Note that the resulting XML document MUST be valid. Therefore, if
the step in applying the <exclude> element value to an XML document
results in an invalid document according to the schema, that step
MUST be reversed, resulting in the elements and/or attributes being
re-introduced into the resulting XML document with their previous
values in order to make it valid. This, in practice, means that a
subscriber defining a filter only needs to <exclude> optional
elements and/or attributes, but SHOULD NOT <exclude> mandatory
elements and/or attributes.

The syntax MUST follow Section 5.

3.5.3. The 'type' Attribute

The 'type' attribute is used to describe the value of the <include>
and <exclude> elements. The following values are pre-defined:
"xpath" and "namespace". The 'type' attribute is optional, and, if
omitted, the default value is "xpath".

The "xpath" value is used when the <include> or <exclude> element
contains a value following the syntax in Section 5 that selects an
element or an attribute.

The "namespace" value is used when the <include> or <exclude> element
contains a value of a namespace. The value is the URI of the
namespace. The resulting XML document is comprised of the elements
defined within the namespace.

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3.6. The <trigger> Element

The <trigger> element is used to identify the package-specific
changes that a resource has to encounter before the content is
delivered to the subscriber. It can appear more than once in a
<filter> element. Multiple appearances of this element denote the
"OR" operation. This means that updates to a resource that satisfy
any of the <trigger> elements criteria constitute the content to be
delivered.

The <trigger> element MAY contain the <changed>, <added>, or
<removed> elements, but it MUST contain at least one of the three
elements. Any combination of the 3 elements is possible. Multiple
appearances of those elements within a <trigger> element denotes the
"AND" operation. This means that updates to a resource that satisfy
ALL of the <changed>, <added>, and <removed> elements' criteria
within the <trigger> element constitute the content to be delivered.

3.6.1. The <changed> Element

The <changed> element is used to identify the XML element or
attribute, from the package-specific XML document, whose value MUST
change from that of the "previous XML document", in order to activate
the trigger and cause the content to be delivered. Previous XML
document" in this context refers to the raw version of the most
recent XML document that was sent to the subscriber, before the
filters were applied to it. The XML element or attribute MUST be
expressed using the syntax defined in Section 5 for the "reference"
ABNF.

The <changed> element MAY contain the 'from' attribute, the 'to'
attribute, the 'by' attribute, or any combination of the three. The
absence of all of those attributes means a change of any sort to the
value of the element or attribute activates the trigger. An update
to the element or attribute value with an identical value is not a
change.

Comparison of a change is done according to the element or
attribute's lexical rules.

3.6.1.1. The 'from' Attribute

A trigger is active when the XML element or attribute identified with
the <changed> element has changed from the value indicated by this
attribute to a different value.

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3.6.1.2. The 'to' Attribute

A trigger is active when the XML element or attribute identified with
the <changed> element has changed to the value indicated by this
attribute from a different value.

3.6.1.3. The 'by' Attribute

A trigger is active when the XML element or attribute identified with
the <changed> element has changed by at least the amount indicated by
this attribute from a different value. That is, the 'by' attribute
applies only to numerical values and indicates a delta with respect
to the current value that an attribute or element (identified in the
<changed> element) needs to change before it is selected. For
example, if the 'by' attribute is set to 2 and the current value of
the element/attribute is 6, the element/attribute is selected when it
reaches (or exceeds) the value 8 or when it decreases to 4 or a lower
value.

3.6.1.4. Combination of Attributes

Any combination of the 'from', 'to', and 'by' attributes in the
<changed> element is possible. For example, if the 'from' attribute
is combined with the 'to' attribute, it is interpreted to mean that
the trigger is active when the XML element or attribute identified
with the <changed> element has changed from the 'from' value to the
'to' value. Note that if the 'by' attribute is used in combination
with the other attributes, the other attribute types MUST match the
'by' type of decimal.

3.6.2. The <added> Element

The <added> element triggers content delivery when the XML element it
identifies has been added to the document being filtered (that is,
this instance of that element appears in the current document, but
not in the previous document). It can be used, for example, to learn
of new services and/or capabilities subscribed to by the user, or
services and/or capabilities that the user has now allowed the
subscriber to see. The XML element or attribute MUST be expressed
using the syntax defined in Section 5 for the "reference" ABNF.

Note that if a filter includes both the content filter (<what>) part
and the <added> element, then the definitions of the <what> part
SHOULD also cover the added elements. Otherwise, the content is
delivered without the items defined in the <added> element.

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3.6.3. The <removed> Element

The <removed> element triggers content delivery when the XML element
it identifies has been removed from the document being filtered (that
is, this instance of that element appeared in the previous document,
but not in this document). The XML element or attribute MUST be
expressed using the syntax defined in Section 5 for the "reference"
ABNF.

4. XML Schema Extensibility

The simple-filter document is meant to be extended. An extension
takes place by defining a new set of elements in a new namespace,
governed by a new schema. Every extension MUST have an appropriate
XML namespace assigned to it. The XML namespace of the extension
MUST be different from the namespaces defined in this specification.
The extension MUST NOT change the syntax or semantics of the schemas
defined in this document. All XML tags and attributes that are part
of the extension MUST be appropriately qualified so as to place them
within that namespace and MUST be designed such that receivers can
safely ignore such extensions.

This specification defines explicit places where new elements or
attributes from an extension can be placed. These are explicitly
indicated in the schemas by the <any> and <anyAttribute> elements.
Extensions to this specification MUST specify where their elements
can be placed within the document.

As a result, a document that contains extensions will require
multiple schemas in order to determine its validity - a schema
defined in this document, along with those defined by extensions
present in the document. Because extensions occur by adding new
elements and attributes governed by new schemas, the schemas defined
in this document are fixed and would only be changed by a revision to
this specification. Such a revision, should it take place, would
endeavor to allow documents compliant to the previous schema to
remain compliant to the new one. As a result, the schemas defined
here don't provide explicit schema versions, as this is not expected
to be needed.

5. Syntax for Referencing XML Items and Making Logical Expressions

The ABNF [10] is used to describe the syntax for the expressions.
The syntax is defined to be XPATH [9] compatible but has only a
restricted set of capabilities of the XPATH. More information about
the meaning of the items of the syntax can be found in [9]. The
"abbreviated syntax" of the "node test" is used in the references
("reference"). The expression in the syntax relates to the

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predicate, comparison, and logical expressions of the XPATH. If an
XPATH expression evaluates to more than one element at a certain
step, the filter applies to all the elements that are evaluated.
That is, if a filter including an element evaluates to 2 elements,
both elements are included as a result.

selection = reference [expression]
expression = "[" (elem-expr / attr-expr)
1*[oper (elem-expr / attr-expr)] "]"
elem-expr = (elem-path / "." / "..") compar value
elem-path = (element / "*") 1*["/" / "*" / element] ["*" / element]
attr-expr = [elem-path "/"] attribute compar value

reference = elem-reference / attr-reference
elem-reference = "/" 1*("/" / "/*" / ("/" element))
attr-reference = reference attribute

oper = "and" / "or"
compar = "=" / "<" / ">"
element = [ns] string
attribute = "@" [ns] string
ns = string ":"
string = <any sequence of data supported by XML in names of XML
element, and/or attribute or prefixes of namespaces>
value = <any sequence of data supported by XML as a value of the
XML element and/or attribute>

When identifying XML elements or attributes, the value may consist of
two parts: the XML element/attribute selector and the condition
(comparison and logical expressions). The XML element selector
appears first followed by the condition part in square brackets. In
the XML element selector part, the XML elements may be referenced by
giving the full hierarchical path as: "/presence/tuple/status/basic",
by denoting the selection to cover any hierarchical level by its name
as: "//tuple/status/basic", or using the wildcard "*", denoting any
value in a certain level as "/*/watcher".

Example references are listed as follows:

o Selecting an element by using an XML element as a condition:
* //*[status/basic="open"]
* /presence/tuple[*/basic="open"]

o Selecting an element by using XML attributes as a condition:
* //watcher[@duration-subscribed<500]
* /*/watcher[@event="rejected"]

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o Selecting an element by using two XML elements as a condition:
* //tuple[status/basic="open" and type="device"]

o Selecting an attribute:
* //watcher/@duration-subscribed

In some cases, due to the design of the XML schema, the XPATH-like
expression results in identification of more than one element with
the same name (the XPATH expression may not have uniquely identified
an element at every step). In those cases, all elements identified
are selected.

When evaluating XPATH location steps, namespace expansion follows
XPATH 1.0 [9] semantics, i.e., if the QName does not have a prefix,
then the namespace URI in the expanded name is null. With
non-default namespaces, expansion is done according to the given
<ns-bindings> definitions. When a default namespace is used in the
document, the <ns-binding> element SHOULD be used to define an equal
URI with some prefix in order to have a valid XPATH evaluation in
location steps.

6. Examples

The XML Schema for the XML document examples is specified in
Section 7.

6.1. Filter Criteria Using <what> Element

A user wishes to get to know his friend's availability and
willingness for messaging (SMS, IM, and MMS) in order to know whether
the friend is able to receive a message, the address to contact, and
the type of the message to be used.

This example shows how to define a content filter. The <basic>
element as well as all parent elements are selected based on a
condition defined by a logical expression. The condition is <class>
elements that have a value "MMS", "SMS", or "IM".

The <class> element is defined in [14] as an extension to PIDF [13].

<?xml version="1.0" encoding="UTF-8"?>
<filter-set xmlns="urn:ietf:params:xml:ns:simple-filter">
<ns-bindings>
<ns-binding prefix="pidf" urn="urn:ietf:params:xml:ns:pidf"/>
<ns-binding prefix="rpid"
urn="urn:ietf:params:xml:ns:pidf:rpid"/>
</ns-bindings>
<filter id="123" uri="sip:[email protected]">

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<what>
<include type="xpath">
/pidf:presence/pidf:tuple[rpid:class="IM" or rpid:class="SMS"
or rpid:class="MMS"]/pidf:status/pidf:basic
</include>
</what>
</filter>
</filter-set>

6.2. Filter Criteria Using <trigger> Element

A user requires to be informed when his colleague becomes available
by some communication means. The user gets the full presence state
of the colleague when a certain PIDF [13] tuple <basic> status
changes from "closed" to "open".

<?xml version="1.0" encoding="UTF-8"?>
<filter-set xmlns="urn:ietf:params:xml:ns:simple-filter">
<ns-bindings>
<ns-binding prefix="pidf" urn="urn:ietf:params:xml:ns:pidf"/>
</ns-bindings>
<filter id="123" uri="sip:[email protected]">
<trigger>
<changed from="CLOSED" to="OPEN">
/pidf:presence/pidf:tuple/pidf:status/pidf:basic
</changed>
</trigger>
</filter>
</filter-set>

6.3. Filter Criteria Using <what> and <trigger> Elements

A user wishes to get information about pending and waiting
subscriptions in order to be able to authorise watchers to see his
presence information.

The filter selects watcher information notifications [16] to be sent
when a subscription status has changed to "pending" or "waiting". In
the notification, only the watchers that have a status of "pending"
or "waiting" are included.

<?xml version="1.0" encoding="UTF-8"?>
<filter-set xmlns="urn:ietf:params:xml:ns:simple-filter">
<ns-bindings>
<ns-binding prefix="wi"
urn="urn:ietf:params:xml:ns:watcherinfo"/>
</ns-bindings>
<filter id="123" uri="sip:[email protected]">

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<what>
<include>
/wi:watcherinfo/wi:watcher-list/wi:watcher[@status="pending"
or @status="waiting"]
</include>
</what>
<trigger>
<changed to="pending">
/wi:watcherinfo/wi:watcher-list/wi:watcher/@status
</changed>
</trigger>
<trigger>
<changed to="waiting">
/wi:watcherinfo/wi:watcher-list/wi:watcher/@status
</changed>
</trigger>
</filter>
</filter-set>

6.4. Content Filter Using Namespaces

A user turns her terminal on, and the terminal automatically fetches
general presence status and information about communication means
from a certain pre-defined set of her buddies.

The filter is defined to select XML elements belonging to the PIDF
namespace.

<?xml version="1.0" encoding="UTF-8"?>
<filter-set xmlns="urn:ietf:params:xml:ns:simple-filter">
<filter id="123" uri="sip:[email protected]">
<what>
<include type="namespace">
urn:ietf:params:xml:ns:pidf
</include>
</what>
</filter>
</filter-set>

6.5. Content Filter Using Only <include> Elements

A user wants to know if a group of his friends is available for
gaming. He orders notifications about the current status and future
changes of the game-specific presence information.

This filter is defined to select the game-specific tuple to be
delivered.

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<?xml version="1.0" encoding="UTF-8"?>
<filter-set xmlns="urn:ietf:params:xml:ns:simple-filter" >
<ns-bindings>
<ns-binding prefix="game-ext"
urn="urn:ietf:params:xml:ns:game-ext"/>
</ns-bindings>
<filter id="123">
<what>
<include>
/pidf:presence/pidf:tuple/
pidf:status[game-ext:label="game-X"]
</include>
</what>
</filter>
</filter-set>

6.6. Two Content Filters as Filter Criteria

The user is interested in getting up-to-date information about the
communication means and contact addresses of his friends. The user
also wants to get more information (e.g., location) about one of the
friends in the list, named Bob. The PIDF element <note> is filtered
out, i.e., excluded. The list was predefined as [email protected].

<?xml version="1.0" encoding="UTF-8"?>
<filter-set xmlns="urn:ietf:params:xml:ns:simple-filter">
<ns-bindings>
<ns-binding prefix="pidf" urn="urn:ietf:params:xml:ns:pidf"/>
<ns-binding prefix="rpid"
urn="urn:ietf:params:xml:ns:pidf:rpid"/>
</ns-bindings>
<filter id="8439" uri="sip:[email protected]">
<what>
<include>
/pidf:presence/pidf:tuple[rpid:class="service"]/pidf:status/
pidf:basic
</include>
</what>
</filter>
<filter id="999" uri="sip:[email protected]">
<what>
<include type="namespace">
urn:ietf:params:xml:ns:pidf
</include>
<exclude>
/pidf:presence/pidf:tuple/pidf:note
</exclude>
</what>

Khartabil, et al. Standards Track [Page 15]

RFC 4661 XML Based Format for Filtering September 2006

</filter>
</filter-set>

7. XML Schema for Filter Criteria

XML Schema Implementation (Normative)

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:simple-filter"
xmlns="urn:ietf:params:xml:ns:simple-filter"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified">

<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>

<xs:annotation>
<xs:documentation xml:lang="en">
XML Schema Definition for Filter Criteria.
</xs:documentation>
</xs:annotation>

<xs:element name="filter-set" type="FilterSetType"/>

<xs:complexType name="FilterSetType">
<xs:sequence>
<xs:element name="ns-bindings" type="NSBindings"
minOccurs="0" maxOccurs="1"/>
<xs:element name="filter" type="FilterType"
minOccurs="1"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="package" type="xs:string" use="optional"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

<xs:complexType name="NSBindings">
<xs:sequence>
<xs:element name="ns-binding" type="NSBinding"
minOccurs="1" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>

<xs:complexType name="NSBinding">
<xs:attribute name="prefix" type="xs:string" use="required"/>
<xs:attribute name="urn" type="xs:anyURI" use="required"/>
</xs:complexType>

Khartabil, et al. Standards Track [Page 16]

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<xs:complexType name="FilterType">
<xs:sequence>
<xs:element name="what" type="WhatType"
minOccurs="0" maxOccurs="1"/>
<xs:element name="trigger" type="TriggerType"
minOccurs="0" maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="id" type="xs:string" use="required"/>
<xs:attribute name="uri" type="xs:anyURI" use="optional"/>
<xs:attribute name="domain" type="xs:string" use="optional"/>
<xs:attribute name="remove" type="xs:boolean" use="optional"
default="false"/>
<xs:attribute name="enabled" type="xs:boolean" use="optional"
default="true"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

<xs:complexType name="WhatType">
<xs:sequence>
<xs:element name="include" type="InclType"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="exclude" type="ExclType"
minOccurs="0" maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>

<xs:complexType name="InclType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="type" type="TypeType"
default="xpath" use="optional"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>

<xs:complexType name="ExclType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="type" type="TypeType"
default="xpath" use="optional"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:simpleContent>

Khartabil, et al. Standards Track [Page 17]

RFC 4661 XML Based Format for Filtering September 2006

</xs:complexType>

<xs:simpleType name="TypeType">
<xs:restriction base="xs:string">
<xs:enumeration value="xpath"/>
<xs:enumeration value="namespace"/>
</xs:restriction>
</xs:simpleType>

<xs:complexType name="TriggerType">
<xs:sequence>
<xs:element name="changed" type="ChangedType"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="added" type="xs:string"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="removed" type="xs:string"
minOccurs="0" maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>

<xs:complexType name="ChangedType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="from" type="xs:anySimpleType"
use="optional"/>
<xs:attribute name="to" type="xs:anySimpleType"
use="optional"/>
<xs:attribute name="by" type="xs:decimal"
use="optional"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>

</xs:schema>

8. Security Considerations

The filters in the body in a SIP message have a significant effect on
the ways in which the request is handled at a server. As a result,
it is especially important that messages containing this extension be
authenticated and authorised. Authentication can be achieved using
the Digest Authentication mechanism described in [12]. The
authorisation decision is based on the permissions that the resource
(notifier) has given to the watcher. An example of such an
auhorisation policy can be found in [18].

Khartabil, et al. Standards Track [Page 18]

RFC 4661 XML Based Format for Filtering September 2006

Requests can reveal sensitive information about a UA's capabilities.
If this information is sensitive, it SHOULD be encrypted using SIP
S/MIME capabilities [11].

All filtering-related security measures discussed in [2] MUST be
followed along with package-specific security.

9. IANA Considerations

This document registers a new MIME type, "application/
simple-filter+xml", and registers a new XML namespace.

This specification follows the guidelines of RFC3023 [7].

9.1. application/simple-filter+xml MIME TYPE

MIME media type: application

MIME subtype name: simple-filter+xml

Mandatory parameters: none

Optional parameters: Same as charset parameter application/xml, as
specified in RFC 3023 [7].

Encoding considerations: Same as encoding considerations of
application/xml, as specified in RFC 3023 [7].

Security considerations: See section 10 of RFC 3023 [7] and section
Section 8 of this document.

Interoperability considerations: none.

Published specification: This document.

Applications that use this media type: This document type has been
used to support the SIP-based Event notification framework and its
packages.

Additional information:

Magic number: None

File extension: .cl or .xml

Macintosh file type code: "TEXT"

Khartabil, et al. Standards Track [Page 19]

RFC 4661 XML Based Format for Filtering September 2006

Personal and email address for further information: Hisham Khartabil
([email protected])

Intended Usage: COMMON

Author/change controller: The IETF

9.2. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:simple-filter

This section registers a new XML namespace, as per guidelines in the
IETF XML Registry [4].

URI: The URI for this namespace is
urn:ietf:params:xml:ns:simple-filter.

Registrant Contact: IETF, SIMPLE working group, Hisham Khartabil
([email protected])

9.3. Schema Registration

This section registers a new XML schema per the procedures in [4].

URI: urn:ietf:params:xml:ns:simple-filter

Registrant Contact: IETF, SIMPLE working group, Hisham Khartabil
([email protected]).

The XML for this schema can be found as the sole content of
Section 7.

10. Acknowledgements

The authors would like to thank Jonathan Rosenberg, Henning
Schulzrinne, Tim Moran, Jari Urpalainen, Sreenivas Addagatla,
Miguel-Angel Garcia Martin, Mary Barnes, Paul Kyzivat, Robert Sparks,
and Elwyn Davies for their valuable input and comments.

11. References

11.1. Normative References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[2] Roach, A. B., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.

Khartabil, et al. Standards Track [Page 20]

RFC 4661 XML Based Format for Filtering September 2006

[3] Khartabil, H., Leppanen, E., Lonnfors, M., and J. Costa-
Requena, "Functional Description of Event Notification
Filtering", RFC 4660, September 2006.

[4] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.

[5] Moats, R., "URN Syntax", RFC 2141, May 1997.

[6] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.

[7] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
RFC 3023, January 2001.

[8] Bray, T., "Exensible Markup Language (XML) 1.0 (Second
Edition)", W3C CR CR-xml11-20011006, October 2000.

[9] Clark, J., "XML Path Language (XPath) Version 1.0", W3C REC
REC-xpath-19991116, November 1999.

[10] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.

[11] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Message Specification", RFC 3851, July
2004.

11.2. Informative References

[12] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.

[13] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and
J. Peterson, "Presence Information Data Format (PIDF)", RFC
3863, August 2004.

[14] Schulzrinne, H., Gurbani, V., Kyzivat, P., and J. Rosenberg,
"RPID -- Rich Presence Extensions to the Presence Information
Data Format (PIDF)", RFC 4480, July 2006.

[15] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004.

[16] Rosenberg, J., "An Extensible Markup Language (XML) Based
Format for Watcher Information", RFC 3858, August 2004.

Khartabil, et al. Standards Track [Page 21]

RFC 4661 XML Based Format for Filtering September 2006

[17] Roach, A. B., Campbell, B., and J. Rosenberg, "A Session
Initiation Protocol (SIP) Event Notification Extension for
Resource Lists", RFC 4663, September 2006.

[18] Rosenberg, J., "Presence Authorization Rules", Work in
Progress, June 2006.

Khartabil, et al. Standards Track [Page 22]

RFC 4661 XML Based Format for Filtering September 2006

Authors' Addresses

Hisham Khartabil
Telio
P.O. Box 1203 Vika
Oslo
Norway

Phone: +47 2167 3544
EMail: [email protected]

Eva Leppanen
Nokia
P.O BOX 785
Tampere
Finland

Phone: +358 7180 77066
EMail: [email protected]

Mikko Lonnfors
Nokia
P.O BOX 321
Helsinki
Finland

Phone: + 358 71800 8000
EMail: [email protected]

Jose Costa-Requena
Nokia
P.O. Box 321
FIN-00045 NOKIA GROUP
FINLAND

Phone: +358 71800 8000
EMail: [email protected]

Khartabil, et al. Standards Track [Page 23]

RFC 4661 XML Based Format for Filtering September 2006

Full Copyright Statement

Copyright (C) The Internet Society (2006).

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat and any
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such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any
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rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
[email protected].

Acknowledgement

Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).

Khartabil, et al. Standards Track [Page 24]