Network Working Group J. Rosenberg

Network Working Group J. Rosenberg
Request for Comments: 4826 Cisco
Category: Standards Track May 2007

Extensible Markup Language (XML)
Formats for Representing Resource Lists

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 IETF Trust (2007).

Abstract

In multimedia communications, presence, and instant messaging
systems, there is a need to define Uniform Resource Identifiers
(URIs) that represent services that are associated with a group of
users. One example is a resource list service. If a user sends a
Session Initiation Protocol (SIP) SUBSCRIBE message to the URI
representing the resource list service, the server will obtain the
state of the users in the associated group, and provide it to the
sender. To facilitate definition of these services, this
specification defines two Extensible Markup Language (XML) documents.
One document contains service URIs, along with their service
definition and a reference to the associated group of users. The
second document contains the user lists that are referenced from the
first. This list of users can be utilized by other applications and
services. Both documents can be created and managed with the XML
Configuration Access Protocol (XCAP).

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Resource Lists Documents . . . . . . . . . . . . . . . . . . . 4
3.1. Structure . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Example Document . . . . . . . . . . . . . . . . . . . . . 9
3.4. Usage with XCAP . . . . . . . . . . . . . . . . . . . . . 10
3.4.1. Application Unique ID . . . . . . . . . . . . . . . . 10
3.4.2. MIME Type . . . . . . . . . . . . . . . . . . . . . . 10
3.4.3. XML Schema . . . . . . . . . . . . . . . . . . . . . . 10
3.4.4. Default Namespace . . . . . . . . . . . . . . . . . . 10
3.4.5. Additional Constraints . . . . . . . . . . . . . . . . 11
3.4.6. Data Semantics . . . . . . . . . . . . . . . . . . . . 11
3.4.7. Naming Conventions . . . . . . . . . . . . . . . . . . 11
3.4.8. Resource Interdependencies . . . . . . . . . . . . . . 12
3.4.9. Authorization Policies . . . . . . . . . . . . . . . . 12
4. RLS Services Documents . . . . . . . . . . . . . . . . . . . . 13
4.1. Structure . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.3. Example Document . . . . . . . . . . . . . . . . . . . . . 15
4.4. Usage with XCAP . . . . . . . . . . . . . . . . . . . . . 16
4.4.1. Application Unique ID . . . . . . . . . . . . . . . . 16
4.4.2. MIME Type . . . . . . . . . . . . . . . . . . . . . . 16
4.4.3. XML Schema . . . . . . . . . . . . . . . . . . . . . . 16
4.4.4. Default Namespace . . . . . . . . . . . . . . . . . . 16
4.4.5. Additional Constraints . . . . . . . . . . . . . . . . 16
4.4.6. Data Semantics . . . . . . . . . . . . . . . . . . . . 17
4.4.7. Naming Conventions . . . . . . . . . . . . . . . . . . 17
4.4.8. Resource Interdependencies . . . . . . . . . . . . . . 18
4.4.9. Authorization Policies . . . . . . . . . . . . . . . . 20
4.5. Usage of an RLS Services Document by an RLS . . . . . . . 20
5. SIP URI Canonicalization . . . . . . . . . . . . . . . . . . . 22
6. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 24
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
8.1. XCAP Application Unique IDs . . . . . . . . . . . . . . . 24
8.1.1. resource-lists . . . . . . . . . . . . . . . . . . . . 24
8.1.2. rls-services . . . . . . . . . . . . . . . . . . . . . 24
8.2. MIME Type Registrations . . . . . . . . . . . . . . . . . 25
8.2.1. application/resource-lists+xml . . . . . . . . . . . . 25
8.2.2. application/rls-services+xml . . . . . . . . . . . . . 26
8.3. URN Sub-Namespace Registrations . . . . . . . . . . . . . 27
8.3.1. urn:ietf:params:xml:ns:resource-lists . . . . . . . . 27
8.3.2. urn:ietf:params:xml:ns:rls-services . . . . . . . . . 28
8.4. Schema Registrations . . . . . . . . . . . . . . . . . . . 28
8.4.1. urn:ietf:params:xml:schema:resource-lists . . . . . . 28

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8.4.2. urn:ietf:params:xml:schema:rls-services . . . . . . . 29
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.1. Normative References . . . . . . . . . . . . . . . . . . . 29
10.2. Informative References . . . . . . . . . . . . . . . . . . 30

1. Introduction

The Session Initiation Protocol (SIP) [4] defines the SIP Uniform
Resource Identifier (URI) as any resource to which a SIP request can
be generated for the purposes of establishing some form of
communications operation. These URIs can represent users (for
example, sip:[email protected]). The SIP URI can also represent a
service, such as voicemail, conferencing, or a presence list. A
common pattern across such SIP services is that the service is
defined, and associated with a URI. In order to operate, that
service needs to make use of a list of users (or, more generally, a
list of resources). When a SIP request is sent to the service URI,
the server providing the service reads that list, and then performs
some kind of operation against each resource on the list. This is
shown in Figure 1.

/---\
| |
\---/ Resource
+----| | List
| | |
| \---/
|
|
|
|
V
+-------------+
| | -------->
| SIP |
---------------> | Service | -------->
service | |
URI | | -------->
+-------------+

Figure 1

One important example of such a service is a presence [11] list
service. A presence list service allows a client to generate a SIP
SUBSCRIBE request to ask for presence information for a list of
users. The presence list server obtains the presence for the users
on the list and provides them back to the client. A presence list

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server is a specific case of a resource list server (RLS) [14], which
allows a client to generate a SIP SUBSCRIBE request to ask for
notifications of SIP events for a list of resources.

Another example of such a service is an instant conference service.
If a client sends a SIP INVITE request to the URI representing the
instance conference service, the conference server will create a
conference call containing the client and the associated group of
users.

It is very useful for a user of these systems to define the groups of
users or resources (generally called a resource list) separately from
the services that access those resource lists. Indeed, there are
usages for resource lists even in the absence of any associated
network-based service. As an example, rather than use a presence
list service, a client might generate individual SUBSCRIBE requests
to obtain the presence of each user in a locally stored presence
list. In such a case, there is a need for a format for storing the
list locally on disk. Furthermore, the user might wish to share the
list with friends, and desire to email it to those friends. This
also requires a standardized format for the resource list.

As such, this document defines two Extensible Markup Language (XML)
document formats. The first is used to represent resource lists,
independent of any particular service. The second is used to define
service URIs for an RLS, and to associate a resource list with the
service URI. This document also defines an XML Configuration Access
Protocol (XCAP) [10] application usage for managing each of these two
documents.

2. Terminology

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.

3. Resource Lists Documents

3.1. Structure

A resource lists document is an XML [2] document 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. Resource lists documents MUST be based on XML 1.0 and MUST
be encoded using UTF-8. This specification makes use of XML
namespaces for identifying resource lists documents and document
fragments. The namespace URI for elements defined by this

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specification is a URN [3] that uses the namespace identifier 'ietf'
defined by RFC 2648 [6] and extended by RFC 3688 [8]. This URN is:

urn:ietf:params:xml:ns:resource-lists

A resource lists document has the <resource-lists> element as the
root element of the document. This element has no attributes. Its
content is a sequence of zero or more <list> elements, each of which
defines a single resource list.

Each <list> element can contain an optional "name" attribute. This
attribute is a handle for the list. When present, it MUST be unique
amongst all other <list> elements within the same parent element.
The <list> element may also contain attributes from other namespaces,
for the purposes of extensibility.

Each <list> element is composed of an optional display name, a
sequence of zero or more elements, each of which may be an <entry>
element, a <list> element, an <entry-ref> element, or an <external>
element, followed by any number of elements from other namespaces,
for the purposes of extensibility. The ability of a <list> element
to contain other <list> elements means that a resource list can be
hierarchically structured. The <display-name> then allows for a
human-friendly name to be associated with each level in the
hierarchy. An <entry> element describes a single resource, defined
by a URI, that is part of the list. An <entry-ref> element allows an
entry in a document within the same XCAP root to be included by
reference, rather than by value. An <external> element contains a
reference to a list stored on this or another server.

The <entry> element describes a single resource. The <entry> element
has a single mandatory attribute, "uri". This attribute is equal to
the URI that is used to access the resource. The resource list
format itself does not constrain the type of URI that can be used.
However, the service making use of the resource list may require
specific URI schemes. For example, RLS services will require URIs
that represent subscribeable resources. This includes the SIP and
pres [15] URIs. The "uri" attribute MUST be unique amongst all other
"uri" attributes in <entry> elements within the same parent.
Uniqueness is determined by case-sensitive string comparisons. As
such, it is possible that two "uri" attributes will have the same URI
when compared using the functional equality rules defined for that
URI scheme, but different ones when compared using case sensitive
string comparison. The <entry> element can also contain attributes
from other namespaces for the purposes of extensibility.

The <entry> element contains a sequence of elements that provide
information about the entry. Only one such element is defined at

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this time, which is <display-name>. This element provides a UTF-8-
encoded string, meant for consumption by a human user, that describes
the resource. Unlike the "name" attribute of the <entry> element,
the <display-name> has no uniqueness requirements. The <display-
name> element can contain the "xml:lang" attribute, which provides
the language of the display name. The <entry> element can contain
other elements from other namespaces. This is meant to support the
inclusion of other information about the entry, such as a phone
number or postal address.

The <entry-ref> element allows an entry to be included in the list by
reference, rather than by value. This element is only meaningful
when the document was obtained through XCAP. In such a case, the
referenced entry has to exist within the same XCAP root. The <entry>
element has a single mandatory attribute, "ref". The "ref" attribute
MUST be unique amongst all other "ref" attributes in <entry-ref>
elements within the same parent. Uniqueness is determined by case
sensitive string comparisons. The <entry-ref> element also allows
attributes from other namespaces, for the purposes of extensibility.
The content of an <entry-ref> element is an optional display name,
followed by any number of elements from other namespaces, for the
purposes of extensibility. The display name is useful for providing
a localized nickname as an alternative to the name defined in the
<entry> to which the <entry-ref> refers.

The content of the "ref" attribute is a relative HTTP URI [7].
Specifically, it MUST be a relative path reference, where the base
URI is equal to the XCAP root URI of the document in which the
<entry-ref> appears. This relative URI, if resolved into an absolute
URI according to the procedures in RFC 3986, MUST resolve to an
<entry> element within a resource-lists document. For example,
suppose that an <entry> element within a specific XCAP root was
identified by the following HTTP URI:

http://xcap.example.com/resource-lists/users/sip:[email protected]/
index/~~/resource-lists/list%5b@name=%22list1%22%5d/
entry%5b@uri=%22sip:[email protected]%22%5d

If http://xcap.example.com is the XCAP root URI, then an <entry-ref>
element pointing to this entry would have the following form:

<entry-ref ref="resource-lists/users/sip:[email protected]/
index/~~/resource-lists/list%5b@name=%22list1%22%5d/
entry%5b@uri=%22sip:[email protected]%22%5d"/>

Note that line folding within the HTTP URI and XML attribute above
are for the purposes of readability only. Also note that, as
described in RFC 3986, the relative path URI does not begin with the

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"/". Since the relative URI used within the "ref" attribute must be
a relative path URI, the "/" will never be present as the first
character within the content of a "ref" attribute. Since the content
of the "ref" attribute is a valid HTTP URI, it must be percent-
encoded within the XML document.

The <external> element is similar to the <entry-ref> element. Like
<entry-ref>, it is only meaningful in documents obtained from an XCAP
server. It too is a reference to content stored elsewhere. However,
it refers to an entire list, and furthermore, it allows that list to
be present on another server. The <external> element has a single
mandatory attribute, "anchor", which specifies the external list by
means of an absolute HTTP URI. The "anchor" attribute MUST be unique
amongst all other "anchor" attributes in <external> elements within
the same parent. Uniqueness is determined by case-sensitive string
comparisons. The <external> element can also contain attributes from
other namespaces, for the purposes of extensibility. The content of
an <external> element is an optional <display-name> followed by any
number of elements from another namespace, for the purposes of
extensibility. The value of the "anchor" attribute MUST be an
absolute HTTP URI. This URI MUST identify an XCAP resource, and in
particular, it MUST represent a <list> element within a resource
lists document. The URI MUST be percent-encoded.

For both the <entry-ref> and <external> elements, the responsibility
of resolving their references falls upon the entity that is making
use of the document. When the document is used in conjunction with
XCAP, this means that the burden falls on the XCAP client. If the
XCAP client is a PC-based application using the resource-lists
document as a presence list, the references would likely be resolved
upon explicit request by the user. They can, of course, be resolved
at any time. If the XCAP client is an RLS itself, the references
would be resolved when the RLS receives a SUBSCRIBE request for an
RLS service associated with a resource list that contains one of
these references (see below). An XCAP server defined by this
specification will not attempt to resolve the references before
returning the document to the client. Similarly, if, due to network
errors or some other problem, the references cannot be resolved, the
handling is specific to the usage of the document. For resource
lists being used by RLS services, the handling is discussed below.

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3.2. Schema

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:resource-lists"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="urn:ietf:params:xml:ns:resource-lists"
elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:complexType name="listType">
<xs:sequence>
<xs:element name="display-name" type="display-nameType"
minOccurs="0"/>
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:choice>
<xs:element name="list">
<xs:complexType>
<xs:complexContent>
<xs:extension base="listType"/>
</xs:complexContent>
</xs:complexType>
</xs:element>
<xs:element name="external" type="externalType"/>
<xs:element name="entry" type="entryType"/>
<xs:element name="entry-ref" type="entry-refType"/>
</xs:choice>
</xs:sequence>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="name" type="xs:string" use="optional"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>
<xs:complexType name="entryType">
<xs:sequence>
<xs:element name="display-name" minOccurs="0">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="display-nameType"/>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="uri" type="xs:anyURI" use="required"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

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<xs:complexType name="entry-refType">
<xs:sequence>
<xs:element name="display-name" type="display-nameType"
minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="ref" type="xs:anyURI" use="required"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>
<xs:complexType name="externalType">
<xs:sequence>
<xs:element name="display-name" type="display-nameType"
minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="anchor" type="xs:anyURI"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>
<xs:element name="resource-lists">
<xs:complexType>
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:element name="list" type="listType"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:complexType name="display-nameType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute ref="xml:lang"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:schema>

3.3. Example Document

The following is an example of a document compliant to the schema.
All line feeds within element content are for display purposes only.

<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<list name="friends">
<entry uri="sip:[email protected]">
<display-name>Bill Doe</display-name>
</entry>

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<entry-ref ref="resource-lists/users/sip:[email protected]/index/~~/
resource-lists/list%5b@name=%22list1%22%5d/entry%5b@uri=%22sip:pet
[email protected]%22%5d"/>
<list name="close-friends">
<display-name>Close Friends</display-name>
<entry uri="sip:[email protected]">
<display-name>Joe Smith</display-name>
</entry>
<entry uri="sip:[email protected]">
<display-name>Nancy Gross</display-name>
</entry>
<external anchor="http://xcap.example.org/resource-lists/users/
sip:[email protected]/index/~~/resource-lists/list%5b@name=%22mkti
ng%22%5d">
<display-name>Marketing</display-name>
</external>
</list>
</list>
</resource-lists>

3.4. Usage with XCAP

Resource lists documents can be manipulated with XCAP. This section
provides the details necessary for such a usage.

3.4.1. Application Unique ID

XCAP requires application usages to define an application unique ID
(AUID) in either the IETF tree or a vendor tree. This specification
defines the "resource-lists" AUID within the IETF tree, via the IANA
registration in Section 8.

3.4.2. MIME Type

The MIME type for this document is "application/resource-lists+xml".

3.4.3. XML Schema

The XML Schema for this document is defined as the sole content of
Section 3.2.

3.4.4. Default Namespace

The default namespace used in expanding URIs is
urn:ietf:params:xml:ns:resource-lists.

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3.4.5. Additional Constraints

In addition to the schema, there are constraints on the values
present in the "name" attribute of the <list> element, the "uri"
attribute of the <external> element, the "ref" attribute of the
<entry-ref> element, and the "anchor" attribute of the <external>
element. These constraints are defined in Section 3.1. Some of
these constraints are enforced by the XCAP server. Those constraints
are:

o The "name" attribute in a <list> element MUST be unique amongst
all other "name" attributes of <list> elements within the same
parent element. Uniqueness is determined by case-sensitive string
comparison.

o The "uri" attribute in a <entry> element MUST be unique amongst
all other "uri" attributes of <entry> elements within the same
parent element. Uniqueness is determined by case-sensitive string
comparison.

o The URI in the "ref" attribute of the <entry-ref> element MUST be
unique amongst all other "ref" attributes of <entry-ref> elements
within the same parent element. Uniqueness is determined by case-
sensitive string comparison. The value of the attribute MUST be a
relative path reference. Note that the server is not responsible
for verifying that the reference resolves to an <entry> element in
a document within the same XCAP root.

o The URI in the "anchor" attribute of the <external> element MUST
be unique amongst all other "anchor" attributes of <external>
elements within the same parent element. Uniqueness is determined
by case-sensitive string comparison. The value of the attribute
MUST be an absolute HTTP URI. Note that the server is not
responsible for verifying that the URI resolves to a <list>
element in a document. Indeed, since the URI may reference a
server in another domain, referential integrity cannot be
guaranteed without adding substantial complexity to the system.

3.4.6. Data Semantics

Semantics for the document content are provided in Section 3.1.

3.4.7. Naming Conventions

Resource lists documents are usually identified as references from
other application usages. For example, an RLS services document
contains a reference to the resource list it uses.

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Frequently, an XCAP client will wish to insert or remove an <entry>,
<entry-ref>, or <external> element from a document without having a
cached copy of that document. In such a case, the "uri" attribute of
the <entry> element, the "ref" attribute of the <entry-ref> element,
or the "anchor" attribute of the <external> element is used as an
index to select the element to operate upon. The XCAP server will
determine uniqueness by case-sensitive string comparison. However,
each of these attributes contain URIs, and the URI equality rules for
their schemes may allow two URIs to be the same, even if they are
different by case sensitive string comparison. As such, it is
possible that a client will attempt a PUT or DELETE in an attempt to
modify or remove an existing element. Instead, the PUT ends up
inserting a new element, or the DELETE ends up returning an error
response.

If the XCAP client cannot determine whether the user intent is to
create or replace, the client SHOULD canonicalize the URI before
performing the operation. For a SIP URI (often present in the "uri"
attribute of the <entry> element), this canonicalization procedure is
defined in Section 5. We expect that the SIP URIs that will be
placed into resource lists documents will usually be of the form
sip:user@domain, and possibly include a user parameter. The
canonicalization rules work perfectly for these URIs.

For HTTP URIs, a basic canonicalization algorithm is as follows. If
the port in the URI is equal to the default port (80 for http URIs),
then the port is removed. The hostname is converted to all
lowercase. Any percent-encoding in the URI for characters which do
not need to be percent-encoded is removed. A character needs to be
percent-encoded when it is not permitted in that part of the URI
based on the grammar for that part of the URI.

3.4.8. Resource Interdependencies

There are no resource interdependencies identified by this
application usage.

3.4.9. Authorization Policies

This application usage does not modify the default XCAP authorization
policy, which is that only a user can read, write, or modify their
own documents. A server can allow privileged users to modify
documents that they don't own, but the establishment and indication
of such policies is outside the scope of this document. It is
anticipated that a future application usage will define which users
are allowed to modify a list resource.

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4. RLS Services Documents

4.1. Structure

An RLS services document is used to define URIs that represent
services provided by a Resource List Server (RLS) as defined in [14].
An RLS services document is an XML [2] document 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. RLS services documents MUST be based on XML 1.0 and MUST
be encoded using UTF-8. This specification makes use of XML
namespaces for identifying RLS services documents and document
fragments. The namespace URI for elements defined by this
specification is a URN [3] that uses the namespace identifier 'ietf'
defined by RFC 2648 [6] and extended by RFC 3688 [8]. This URN is:

urn:ietf:params:xml:ns:rls-services

The root element of an rls-services document is <rls-services>. It
contains a sequence of <service> elements, each of which defines a
service available at an RLS.

Each <service> element has a single mandatory attribute, "uri". This
URI defines the resource associated with the service. That is, if a
client subscribes to that URI, they will obtain the service defined
by the corresponding <service> element. The <service> element can
also contain attributes from other namespaces, for the purposes of
extensibility. The <service> element contains child elements that
define the service. For an RLS service, very little service
definition is needed: just the resource list to which the server will
perform virtual subscriptions [14] and the set of event packages that
the service supports. The former can be conveyed in one of two ways.
There can be a <resource-list> element, which points to a <list>
element in a resource-lists document, or there can be a <list>
element, which includes the resource list directly. The supported
packages are contained in the <packages> element. The <service>
element can also contain elements from other namespaces, for the
purposes of extensibility.

By including the contents of the resource list directly, a user can
create lists and add members to them with a single XCAP operation.
However, the resulting list becomes "hidden" within the RLS service
definition, and is not usable by other application usages. For this
reason, the <resource-list> element exists as an alternative. It can
reference a <list> element in a resource-lists document. Since the
list is separated from the service definition, it can be easily
reused by other application usages.

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The <list> element is of the list type defined by the schema for
resource lists. It is discussed in Section 3.1.

The <resource-list> element contains a URI. This element is only
meaningful when the document was obtained through XCAP. The URI MUST
be an absolute HTTP URI representing an XCAP element resource. Its
XCAP root MUST be the same as the XCAP root of the RLS services
document. When the RLS services document is present in a user's home
directory, the HTTP URI MUST exist underneath that user's home
directory in the resource-lists application usage. When the RLS
services document is in the global directory, the HTTP URI MUST exist
underneath any user's home directory in the resource-lists
application usage. In either case, the element referenced by the URI
MUST be a <list> element within a resource-lists document. All of
these constraints except for the latter one (which is a referential
integrity constraint) will be enforced by the XCAP server.

The <packages> element contains a sequence of <package> elements.
The content of each <package> element is the name of a SIP event
package [13]. The <packages> element may also contain elements from
additional namespaces, for the purposes of extensibility. The
<packages> element is optional. When it is not present, it means
that the RLS service will accept subscriptions for any event package.

4.2. Schema

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:rls-services"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="urn:ietf:params:xml:ns:rls-services"
xmlns:rl="urn:ietf:params:xml:ns:resource-lists"
elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:element name="rls-services">
<xs:complexType>
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:element name="service" type="serviceType"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:complexType name="serviceType">
<xs:sequence>
<xs:choice>
<xs:element name="resource-list" type="xs:anyURI"/>
<xs:element name="list" type="rl:listType"/>
</xs:choice>
<xs:element name="packages" type="packagesType" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>

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</xs:sequence>
<xs:attribute name="uri" type="xs:anyURI" use="required"/>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>
<xs:complexType name="packagesType">
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:element name="package" type="packageType"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:simpleType name="packageType">
<xs:restriction base="xs:string"/>
</xs:simpleType>
</xs:schema>

4.3. Example Document

This document shows two services. One is sip:[email protected],
and the other is sip:[email protected]. The former service
references a resource list in a resource-lists document, and the
latter one includes a list locally. Both services are for the
presence event package only.

<?xml version="1.0" encoding="UTF-8"?>
<rls-services xmlns="urn:ietf:params:xml:ns:rls-services"
xmlns:rl="urn:ietf:params:xml:ns:resource-lists"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<service uri="sip:[email protected]">
<resource-list>http://xcap.example.com/resource-lists/user
s/sip:[email protected]/index/~~/resource-lists/list%5b@nam
e=%22l1%22%5d</resource-list>
<packages>
<package>presence</package>
</packages>
</service>
<service uri="sip:[email protected]">
<list name="marketing">
<rl:entry uri="sip:[email protected]"/>
<rl:entry uri="sip:[email protected]"/>
</list>
<packages>
<package>presence</package>
</packages>
</service>
</rls-services>

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4.4. Usage with XCAP

RLS services documents can be manipulated with XCAP. This section
provides the details necessary for such a usage.

4.4.1. Application Unique ID

XCAP requires application usages to define an application unique ID
ID (AUID) in either the IETF tree or a vendor tree. This
specification defines the "rls-services" AUID within the IETF tree,
via the IANA registration in Section 8.

4.4.2. MIME Type

The MIME type for this document is "application/rls-services+xml".

4.4.3. XML Schema

The XML Schema for this document is defined as the sole content of
Section 4.2.

4.4.4. Default Namespace

The default namespace used in expanding URIs is
urn:ietf:params:xml:ns:rls-services.

4.4.5. Additional Constraints

In addition to the schema, there are constraints on the URIs present
in the <service> and <resource-list> elements. These constraints are
defined in Section 3.1. Some of these constraints are enforced by
the XCAP server. Those constraints are:

o The URI in the "uri" attribute of the <service> element MUST be
unique amongst all other URIs in "uri" elements in any <service>
element in any document on a particular server. This uniqueness
constraint spans across XCAP roots. Furthermore, the URI MUST NOT
correspond to an existing resource within the domain of the URI.
If a server is asked to set the URI to something that already
exists, the server MUST reject the request with a 409, and use the
mechanisms defined in [10] to suggest alternate URIs that have not
yet been allocated.

o The URI in a <resource-list> element MUST be an absolute URI. The
server MUST verify that the URI path contains "resource-lists" in
the path segment corresponding to the AUID. If the RLS services
document is within the XCAP user tree (as opposed to the global
tree), the server MUST verify that the XUI in the path is the same

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as the XUI in the URI of to the RLS services document. These
checks are made by examining the URI value, as opposed to
dereferencing the URI. The server is not responsible for
verifying that the URI actually points to a <list> element within
a valid resource lists document.

o In addition, an RLS services document can contain a <list>
element, which in turn can contain <entry>, <entry-ref>, <list>,
and <external> elements. The constraints defined for these
elements in Section 3.4.7 MUST be enforced.

o In some cases, an XCAP client will wish to create a new RLS
service, and wish to assign it a "vanity URI", such as
sip:[email protected]. However, the client does not know
whether this URI meets the uniqueness constraints defined above.
In that case, it can simply attempt the creation operation, and if
the result is a 409 that contains a detailed conflict report with
the <uniqueness-failure> element, the client knows that the URI
could not be assigned. It can then retry with a different vanity
URI, or use one of the suggestions in the detailed conflict
report.

o If the client wishes to create a new RLS service, and it doesn't
care what the URI is, the client creates a random one, and
attempts the creation operation. As discussed in [10], if this
should fail with a uniqueness conflict, the client can retry with
different URIs with increasing randomness.

4.4.6. Data Semantics

Semantics for the document content are provided in Section 4.1.

4.4.7. Naming Conventions

Typically, there are two distinct XCAP clients that access RLS
services documents. The first is a client acting on behalf of the
end user in the system. This client edits and writes both resource
lists and RLS services documents as they are created or modified by
the end user. The other XCAP client is the RLS itself, which reads
the RLS services documents in order to process SUBSCRIBE requests.

To make it easier for an RLS to find the <service> element for a
particular URI, the XCAP server maintains, within the global tree, a
single RLS services document representing the union of all the
<service> elements across all documents created by all users within
the same XCAP root. There is a single instance of this document, and
its name is "index". Thus, if the root services URI is

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http://xcap.example.com, the following is the URI that an RLS would
use to fetch this index:

http://xcap.example.com/rls-services/global/index

As discussed below, this index is created from all the documents in
the user tree that have the name "index" as well. An implication of
this is that a client operating on behalf of a user SHOULD define its
RLS services within the document named "index". If the root services
URI is http://xcap.example.com, for user "sip:[email protected]" the
URI for this document would be:

http://xcap.example.com/rls-services/users/sip:[email protected]/index

If a client elects to define RLS services in a different document,
this document will not be "picked up" in the global index, and
therefore, will not be used as an RLS service.

4.4.8. Resource Interdependencies

As with other application usages, the XML schema and the XCAP
resource naming conventions describe most of the resource
interdependencies applicable to this application usage.

This application usage defines an additional resource interdependence
between a single document in the global tree and all documents in the
user tree with the name "index". This global document is formed as
the union of all of the index documents for all users within the same
XCAP root. In this case, the union operation implies that each
<service> element in a user document will also be present as a
<service> element in the global document. The inverse is true as
well. Every <service> element in the global document exists within a
user document within the same XCAP root.

As an example, consider the RLS services document for user
sip:[email protected]:

<?xml version="1.0" encoding="UTF-8"?>
<rls-services>
<service uri="sip:[email protected]">
<resource-list>http://xcap.example.com/resource-lists/users/si
p:[email protected]/index/~~/resource-lists/list%5b@name=%22l1%
22%5d</resource-list>
<packages>
<package>presence</package>
</packages>
</service>
</rls-services>

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And consider the RLS services document for user bob:

<?xml version="1.0" encoding="UTF-8"?>
<rls-services>
<service uri="sip:[email protected]">
<list name="marketing">
<rl:entry uri="sip:[email protected]"/>
<rl:entry uri="sip:[email protected]"/>
</list>
<packages>
<package>presence</package>
</packages>
</service>
</rls-services>

The global document at
http://xcap.example.com/rls-services/global/index would look like
this:

<?xml version="1.0" encoding="UTF-8"?>
<rls-services xmlns="urn:ietf:params:xml:ns:rls-services"
xmlns:rl="urn:ietf:params:xml:ns:resource-lists"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<service uri="sip:[email protected]">
<resource-list>http://xcap.example.com/resource-lists/user
s/sip:[email protected]/index/~~/resource-lists/list%5b@nam
e=%22l1%22%5d</resource-list>
<packages>
<package>presence</package>
</packages>
</service>
<service uri="sip:[email protected]">
<list name="marketing">
<rl:entry uri="sip:[email protected]"/>
<rl:entry uri="sip:[email protected]"/>
</list>
<packages>
<package>presence</package>
</packages>
</service>
</rls-services>

Requests made against the global document MUST generate responses
that reflect the most recent state of all the relevant user
documents. This requirement does not imply that the server must
actually store this global document. It is anticipated that most
systems will dynamically construct the responses to any particular
request against the document resource.

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The uniqueness constraint on the "uri" attribute of <service> will
ensure that no two <service> elements in the global document have the
same value of that attribute.

4.4.9. Authorization Policies

This application usage does not modify the default XCAP authorization
policy, which is that only a user can read, write, or modify their
own documents. A server can allow privileged users to modify
documents that they don't own, but the establishment and indication
of such policies are outside the scope of this document. It is
anticipated that a future application usage will define which users
are allowed to modify an RLS services document.

The index document maintained in the global tree represents sensitive
information, as it contains the union of all the information for all
users on the server. As such, its access MUST be restricted to
trusted elements within domain of the server. Typically, this would
be limited to the RLSs that need access to this document.

4.5. Usage of an RLS Services Document by an RLS

This section discusses how an RLS, on receipt of a SUBSCRIBE request,
uses XCAP and the RLS services document to guide its operation.

When an RLS receives a SUBSCRIBE request for a URI (present in the
Request URI), it obtains the <service> element whose uri attribute
matches (based on URI equality) the URI in the SUBSCRIBE request.
This document makes no normative statements on how this might be
accomplished. The following paragraph provides one possible
approach.

The RLS canonicalizes the Request URI as described in Section 5. It
then performs an XCAP GET operation against the URI formed by
combining the XCAP root with the document selector of the global
index with a node selector of the form "rls-services/
service[@uri=<canonical-uri>]", where <canonical-uri> is the
canonicalized version of the Request URI. If the response is a 200
OK, it will contain the service definition for that URI.

Once the <service> element has been obtained, it is examined. If the
<packages> element is present, and the event package in the SUBSCRIBE
request is not amongst those listed in the <package> elements within
<packages>, the request MUST be rejected with a 489 (Bad Event)
response code, as described in [13]. Otherwise, it SHOULD be
processed. The next step is to authorize that the client is allowed
to subscribe to the resource. This can be done using the data
defined in [12], for example. Assuming the subscriber is authorized

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to subscribe to that resource, the subscription is processed
according to the procedures defined in [14]. This processing
requires the RLS to compute a flat list of URIs that are to be
subscribed to. If the <service> element had a <list> element, it is
extracted. If the <service> element had a <resource-list> element,
its URI content is dereferenced. The result should be a <list>
element. If it is not, the request SHOULD be rejected with a 502
(Bad Gateway). Otherwise, that <list> element is extracted.

At this point, the RLS has a <list> element in its possession. The
next step is to obtain a flat list of URIs from this element. To do
that, it traverses the tree of elements rooted in the <list> element.
Before traversal begins, the RLS initializes two lists: the "flat
list", which will contain the flat list of the URI after traversal,
and the "traversed list", which contains a list of HTTP URIs in
<external> elements that have already been visited. Both lists are
initially empty. Next, tree traversal begins. A server can use any
tree-traversal ordering it likes, such as depth-first search or
breadth-first search. The processing at each element in the tree
depends on the name of the element:

o If the element is <entry>, the URI in the "uri" attribute of the
element is added to the flat list if it is not already present
(based on case-sensitive string equality) in that list, and the
URI scheme represents one that can be used to service
subscriptions, such as SIP [4] and pres [15].

o If the element is an <entry-ref>, the relative path reference
making up the value of the "ref" attribute is resolved into an
absolute URI. This is done using the procedures defined in
Section 5.2 of RFC 3986 [7], using the XCAP root of the RLS
services document as the base URI. This absolute URI is resolved.
If the result is not a 200 OK containing a <entry> element, the
SUBSCRIBE request SHOULD be rejected with a 502 (Bad Gateway).
Otherwise, the <entry> element returned is processed as described
in the previous step.

o If the element is an <external> element, the absolute URI making
up the value of the "anchor" attribute of the element is examined.
If the URI is on the traversed list, the server MUST cease
traversing the tree, and SHOULD reject the SUBSCRIBE request with
a 502 (Bad Gateway). If the URI is not on the traversed list, the
server adds the URI to the traversed list, and dereferences the
URI. If the result is not a 200 OK containing a <list> element,
the SUBSCRIBE request SHOULD be rejected with a 502 (Bad Gateway).
Otherwise, the RLS replaces the <external> element in its local
copy of the tree with the <list> element that was returned, and
tree traversal continues.

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Because the <external> element is used to dynamically construct the
tree, there is a possibility of recursive evaluation of references.
The traversed list is used to prevent this from happening.

Once the tree has been traversed, the RLS can create virtual
subscriptions to each URI in the flat list, as defined in [14]. In
the processing steps outlined above, when an <entry-ref> or
<external> element contains a reference that cannot be resolved,
failing the request is at SHOULD strength. In some cases, an RLS may
provide better service by creating virtual subscriptions to the URIs
in the flat list that could be obtained, omitting those that could
not. Only in those cases should the SHOULD recommendation be
ignored.

5. SIP URI Canonicalization

This section provides a technique for URI canonicalization. This
canonicalization produces a URI that, in most cases, is equal to the
original URI (where equality is based on the URI comparison rules in
RFC 3261). Furthermore, the canonicalized URI will usually be
lexically equivalent to the canonicalized version of any other URI
equal to the original.

To canonicalize the URI, the following steps are followed:

1. First, the domain part of the URI is converted into all
lowercase, and any tokens (such as "user" or "transport" or
"udp") are converted to all lowercase.

2. Secondly, any percent-encoding in the URI for characters which do
not need to be percent-encoded is removed. A character needs to
be percent-encoded when it is not permitted in that part of the
URI based on the grammar for that part of the URI. For example,
if a SIP URI is sip:%6aoe%[email protected], it is changed to
sip:joe%[email protected]. In the original URI, the character
'j' was percent-encoded. This is allowed, but not required,
since the grammar allows a 'j' to appear in the user part. As a
result, it appears as 'j' after this step of canonicalization.

3. Thirdly, any URI parameters are reordered so that they appear in
lexical order based on parameter name. The ordering of a
character is determined by the US-ASCII numerical value of that
character, with smaller numbers coming first. Parameters are
ordered with the leftmost character as most significant. For
parameters that contain only letters, this is equivalent to an
alphabetical ordering.

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4. Finally, any header parameters are discarded. This canonicalized
URI is used instead of the original URI.

If two URIs, A and B, are functionally equal (meaning that they are
equal according to the URI comparison rules in RFC 3261), their
canonicalized URIs are equal under case-sensitive string comparison
if the following are true:

o Neither URI contains header parameters.

o If one of the URI contains a URI parameter not defined in RFC
3261, the other does as well.

6. Extensibility

Resource-lists and RLS services documents are 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.

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.

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7. Security Considerations

The information contained in rls-services and resource-lists
documents are particularly sensitive. It represents the principle
set of people with whom a user would like to communicate. As a
result, clients SHOULD use TLS when contacting servers in order to
fetch this information. Note that this does not represent a change
in requirement strength from XCAP.

8. IANA Considerations

There are several IANA considerations associated with this
specification.

8.1. XCAP Application Unique IDs

This section registers two new XCAP Application Unique IDs (AUIDs)
according to the IANA procedures defined in [10].

8.1.1. resource-lists

Name of the AUID: resource-lists

Description: A resource lists application is any application that
needs access to a list of resources, identified by a URI, to which
operations, such as subscriptions, can be applied.

8.1.2. rls-services

Name of the AUID: rls-services

Description: A Resource List Server (RLS) services application is a
Session Initiation Protocol (SIP) application whereby a server
receives SIP SUBSCRIBE requests for resource, and generates
subscriptions towards a resource list.

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8.2. MIME Type Registrations

This specification requests the registration of two new MIME types
according to the procedures of RFC 4288 [9] and guidelines in RFC
3023 [5].

8.2.1. application/resource-lists+xml

MIME media type name: application

MIME subtype name: resource-lists+xml

Mandatory parameters: none

Optional parameters: Same as charset parameter application/xml as
specified in RFC 3023 [5].

Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [5].

Security considerations: See Section 10 of RFC 3023 [5] and
Section 7 of RFC 4826.

Interoperability considerations: none

Published specification: RFC 4826

Applications that use this media type: This document type has been
used to support subscriptions to lists of users [14] for SIP-based
presence [11].

Additional Information:

Magic Number: none

File Extension: .rl

Macintosh file type code: "TEXT"

Personal and email address for further information:
Jonathan Rosenberg, [email protected]

Intended usage: COMMON

Author/Change controller: The IETF.

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8.2.2. application/rls-services+xml

MIME media type name: application

MIME subtype name: rls-services+xml

Mandatory parameters: none

Optional parameters: Same as charset parameter application/xml as
specified in RFC 3023 [5].

Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [5].

Security considerations: See Section 10 of RFC 3023 [5] and
Section 7 of RFC 4826.

Interoperability considerations: none

Published specification: RFC 4826

Applications that use this media type: This document type has been
used to support subscriptions to lists of users [14] for SIP-based
presence [11].

Additional Information:

Magic Number: none

File Extension: .rs

Macintosh file type code: "TEXT"

Personal and email address for further information:
Jonathan Rosenberg, [email protected]

Intended usage: COMMON

Author/Change controller: The IETF.

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8.3. URN Sub-Namespace Registrations

This section registers two new XML namespaces, as per the guidelines
in RFC 3688 [8].

8.3.1. urn:ietf:params:xml:ns:resource-lists

URI: The URI for this namespace is
urn:ietf:params:xml:ns:resource-lists.

Registrant Contact: IETF, SIMPLE working group, ([email protected]),
Jonathan Rosenberg ([email protected]).

XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Resource Lists Namespace</title>
</head>
<body>
<h1>Namespace for Resource Lists</h1>
<h2>urn:ietf:params:xml:ns:resource-lists</h2>
<p>See <a href="http://www.rfc-editor.org/rfc/rfc4826.txt">
RFC4826</a>.</p>
</body>
</html>
END

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8.3.2. urn:ietf:params:xml:ns:rls-services

URI: The URI for this namespace is
urn:ietf:params:xml:ns:rls-services.

Registrant Contact: IETF, SIMPLE working group, ([email protected]),
Jonathan Rosenberg ([email protected]).

XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Resource List Server (RLS) Services Namespace</title>
</head>
<body>
<h1>Namespace for Resource List Server (RLS) Services</h1>
<h2>urn:ietf:params:xml:ns:rls-services</h2>
<p>See <a href="http://www.rfc-editor.org/rfc/rfc4826.txt">
RFC4826</a>.</p>
</body>
</html>
END

8.4. Schema Registrations

This section registers two XML schemas per the procedures in [8].

8.4.1. urn:ietf:params:xml:schema:resource-lists

URI: urn:ietf:params:xml:schema:resource-lists

Registrant Contact: IETF, SIMPLE working group, ([email protected]),
Jonathan Rosenberg ([email protected]).

The XML for this schema can be found as the sole content of
Section 3.2.

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8.4.2. urn:ietf:params:xml:schema:rls-services

URI: urn:ietf:params:xml:schema:rls-services

Registrant Contact: IETF, SIMPLE working group, ([email protected]),
Jonathan Rosenberg ([email protected]).

The XML for this schema can be found as the sole content of
Section 4.2.

9. Acknowledgements

The authors would like to thank Hisham Khartabil, Jari Urpalainen,
and Spencer Dawkins for their comments and input. Thanks to Ted
Hardie for his encouragement and support of this work.

10. References

10.1. Normative References

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

[2] Paoli, J., Maler, E., Bray, T., and C. Sperberg-McQueen,
"Extensible Markup Language (XML) 1.0 (Second Edition)", World
Wide Web Consortium FirstEdition REC-xml-20001006,
October 2000, <http://www.w3.org/TR/2000/REC-xml-20001006>.

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

[4] 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.

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

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

[7] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
January 2005.

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

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RFC 4826 XML Resource Lists May 2007

[9] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.

[10] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)", RFC 4825, May 2007.

10.2. Informative References

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

[12] Rosenberg, J., "Presence Authorization Rules", Work
in Progress, October 2006.

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

[14] Roach, A., Rosenberg, J., and B. Campbell, "A Session
Initiation Protocol (SIP) Event Notification Extension for
Resource Lists", RFC 4662, January 2005.

[15] Peterson, J., "Common Profile for Presence (CPP)", RFC 3859,
August 2004.

Author's Address

Jonathan Rosenberg
Cisco
Edison, NJ
US

EMail: [email protected]
URI: http://www.jdrosen.net

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RFC 4826 XML Resource Lists May 2007

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