SIMPLE J. Rosenberg
Internet-Draft Cisco
Intended status: Standards Track J. Urpalainen
Expires: February 18, 2008 Nokia
August 17, 2007
An Extensible Markup Language (XML) Document Format for Indicating A
Change in XML Configuration Access Protocol (XCAP) Resources
draft-ietf-simple-xcap-diff-06
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This specification defines a document format that can be used to
indicate that a change has occurred in a document managed by the
Extensible Markup Language (XML) Configuration Access Protocol
(XCAP). This format indicates the document that has changed and its
former and new entity tags. It also can indicate the specific change
that was made in the document, using an XML patch format. This
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format allows also indications of element and attribute content of an
XML document. XCAP diff documents can be delivered to clients using
a number of means, including a Session Initiation Protocol (SIP)
event package.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Structure of an XCAP Diff Document . . . . . . . . . . . . . . 4
4. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Example Document . . . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7.1. application/xcap-diff+xml MIME Type . . . . . . . . . . . 11
7.2. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:xcap-diff . . . . . . . . . . . . . 12
7.3. Schema Registration . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
The Extensible Markup Language (XML) Configuration Access Protocol
(XCAP) [9] is a protocol that allows clients to manipulate XML
documents stored on a server. These XML documents serve as
configuration information for application protocols. As an example,
resource list [13] subscriptions (also known as presence lists) allow
a client to have a single SIP subscription to a list of users, where
the list is maintained on a server. The server will obtain presence
for those users and report it back to the client. This application
requires the server, called a Resource List Server (RLS), to have
access to the list of presentities. This list needs to be
manipulated by clients so they can add and remove their friends as
they desire.
Complexities arise when multiple clients attempt to simultaneously
manipulate a document, such as a presence list. Frequently, a client
will keep a copy of the current list in memory, so it can render it
to users. However, if another client modifies the document, the
cached version becomes stale. This modification event must be made
known to all clients which have cached copies of the document, so
that they can fetch the most recent one.
To deal with this problem, clients can use a Session Initiation
Protocol (SIP) [11] event package [12] to subscribe to change events
in XCAP documents. This notification needs to indicate the specific
resource that changed, and how it changed. One solution for the
format of such a change notification would be a content indirection
object [15]. Though content indirection can tell a client that a
document has changed, it provides it with MIME Content-ID indicating
the new version of the document. The MIME Content-ID is not the same
as the entity tag, which is used by XCAP for document versioning. As
such, a client cannot easily ascertain whether an indication of a
change in a document is due to a change it just made, or due to a
change another client made at around the same time. Furthermore,
content indirections don't indicate how a document changed; they
would only be able to indicate that it did change.
To resolve these problems, this document defines a data format which
can convey the fact that an XML document managed by XCAP has changed.
This data format is an XML document format, called an XCAP diff
document. This format can indicate that a document has changed, and
provide its previous and new entity tags. It can also optionally
include a set of patch operations [10], which indicate how to
transform the document from the version prior to the change, to the
version after it. XML element and attribute content of XCAP
documents can also be delivered with this format.
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XML documents that are equivalent for the purposes of many
applications may differ in their physical representation. Similar to
XCAP, the canonical form with comments [1] of an XML document
determines the logical equivalence when this format is used to patch
XML 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 [8] and
indicate requirement levels for compliant implementations.
This specification also defines the following additional terms:
Document: When the term document is used without the "XCAP diff" in
front of it, it refers to the XCAP document resource about whom
the XCAP diff document is reporting a change.
XCAP diff document: The XML document defined by this specification
that reports on a set of changes in an XCAP document resource.
Server: Typically an XCAP server, this is a protocol entity that
generates XCAP diff documents based on its knowledge of a set of
XCAP documents.
Client: Typically an XCAP client and SIP User Agent (UA), the client
consumes XCAP diff documents in order to reconstruct the document
stored on the server.
3. Structure of an XCAP Diff Document
An XCAP diff document is an XML [2] document that MUST be well-formed
and SHOULD be valid. XCAP diff documents MUST be based on XML 1.0
and MUST be encoded using UTF-8. This specification makes use of XML
namespaces for identifying XCAP diff documents and document
fragments. The namespace URI for elements defined by this
specification is a URN [4], using the namespace identifier 'ietf'
defined by [6] and extended by [7]. This URN is:
urn:ietf:params:xml:ns:xcap-diff
An XCAP diff document begins with the root element tag <xcap-diff>.
This element has a single mandatory attribute, "xcap-root". The
value of this attribute is the XCAP root URI for the documents in
which the changes have taken place. A single XCAP diff document can
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only represent changes in documents within the same XCAP root. The
content of the <xcap-diff> element is an unordered sequence of
<document>, <element> and <attribute> elements followed by any number
of elements from other namespaces for the purposes of extensibility.
Any such unknown elements MUST be ignored by the client. Each
<document> element specifies changes in a specific document within
the XCAP root. It has one mandatory attribute, "sel", and a two
optional attributes, "new-etag" and "previous-etag". The "sel"
attribute of the <document> element identifies the specific document
within the XCAP root for which changes are indicated. Its content
MUST be a relative path reference, with the base URI being equal to
the XCAP root URI. The "new-etag" attribute provides the entity tag
(ETag) for the document after the application of the changes,
assuming the document exists after those changes. The "previous-
etag" attribute provides an identifier for the document instance
prior to the change. If the change being reported is the removal of
a document, the "previous-etag" MUST only be included and the "new-
etag" attribute will not be present. The "new-etag" attribute MUST
only exist alone when the document either exists or it was just
created (no patch included). Both attributes are present when a
patch (or series of XCAP operations) has been applied to the
resource. Also both attributes MAY be used to indicate an ETag
change without any document modifications (patches).
The "previous-etag" and "new-etag" need not have been sequentially
assigned ETags at the server. An XCAP diff document can indicate
changes that have occurred over a series of XCAP operations. The
only requirement then is that, the sequence of events, when executed
serially, will result in the transformation of the document with the
ETag "previous-etag" to the one whose ETag is "new-etag". Also the
series of operations do not have to be the same exact series of
operations that occurred at the server.
Each <document> element contains either a sequence of patching
instructions or an indication that the body hasn't semantically
changed. The latter means that the document has been assigned a new
ETag but its content is unchanged and it is indicated by the <body-
not-changed> element. Patching instructions are described by the
<add>, <replace> and <remove> elements. These elements use the
corresponding add, replace and remove types defined in [10], and
define a set of patch operations that can be applied to transform the
document. See [10] for instructions on how this transformation is
effected. The <document> element can also contain elements from
other namespaces for the purposes of extensibility. Any unknown
elements MUST be ignored.
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Figure 1 shows <document> element content and how corresponding
resource or metadata changes. An external document retrieval means
in practice an HTTP GET requests for a relevant resource.
+-----------+----------+-----------+----------+-------------------+
| previous- | new- | <add> | <body- | XCAP resource/ |
| etag | etag | <replace> | not- | metadata change |
| | | <remove> | changed> | |
+-----------+----------+-----------+----------+-------------------+
| xxx | yyy | * | - | resource patched, |
| | | | | patch included |
+-----------+----------+-----------+----------+-------------------+
| xxx | yyy | - | - | resource patched, |
| | | | | external document |
| | | | | retrieval |
+-----------+----------+-----------+----------+-------------------+
| xxx | yyy | - | * | only ETag changed |
+-----------+----------+-----------+----------+-------------------+
| - | yyy | - | - | resource created |
| | | | | or exists, |
| | | | | external document |
| | | | | retrieval |
+-----------+----------+-----------+----------+-------------------+
| xxx | - | - | - | resource removed |
+-----------+----------+-----------+----------+-------------------+
Figure 1: <document> element content / corresponding resource changes
Each <element> element indicates the existing element content of an
XCAP document. It has one mandatory attribute, "sel", and one
optional attribute, "exists". The "sel" attribute of the <element>
element identifies an XML element of an XCAP document. It is a
percent endoced relative URI following XCAP conventions when
selecting elements. The XCAP Node Selector MUST always locate a
unique node, the "exists" attribute thus shows whether an element
exists or not in the XCAP document. When the "exists" attribute is
absent from the <element> element, the indicated element still exists
in the XCAP document. The located result element exists as a child
element of the <element> element. It should be noted, that only the
full content of an element is shown if it exists, there are no
conventions for patching these elements. In a corner case where the
content of this element cannot be presented for some reason, although
it exists in the XCAP document, the <element> element MUST not have
any child nodes.
As the result XML element is typically namespace qualified, all
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needed namespace declarations MUST exist within the <xml-diff>
document. The possible local namespace declarations within the
result element exist unmodified as in the source document, similar to
XCAP conventions. Other namespace references MUST be resolved from
the context of the <element> or its parent elements. The prefixes of
qualified names (QName) [3] of XML nodes also remain as they exist
originally in the source XCAP document.
Each <attribute> element indicates the existing attribute content of
an XCAP document. It has one mandatory attribute, "sel", and one
optional attribute, "exists". The "sel" attribute of the <attribute>
element identifies an XML attribute of an XCAP document. It is a
percent endoced relative URI following XCAP conventions when
selecting attributes. The "exists" attribute indicates whether an
attribute exists or not in the XCAP document. When the "exists"
attribute is absent from the <attribute> element, the indicated
attribute exists in the XCAP document. The child text node of the
<attribute> element indicates the value of the located attribute.
4. XML Schema
The XML Schema for the XCAP diff format.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="urn:ietf:params:xml:ns:xcap-diff"
targetNamespace="urn:ietf:params:xml:ns:xcap-diff"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- include patch-ops -->
<xs:include
schemaLocation="urn:ietf:params:xml:schema:xml-patch-ops"/>
<!-- document root -->
<xs:element name="xcap-diff">
<xs:complexType>
<xs:sequence minOccurs="0">
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:choice>
<xs:element name="document" type="documentType"/>
<xs:element name="element" type="elementType"/>
<xs:element name="attribute" type="attributeType"/>
</xs:choice>
</xs:sequence>
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<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="xcap-root" type="xs:anyURI" use="required"/>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>
</xs:element>
<!-- xcap document type -->
<xs:complexType name="documentType">
<xs:choice minOccurs="0">
<xs:element name="body-not-changed" type="emptyType"/>
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:choice>
<xs:element name="add">
<xs:complexType>
<xs:complexContent>
<xs:extension base="add">
<xs:anyAttribute processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
<xs:element name="remove">
<xs:complexType>
<xs:complexContent>
<xs:extension base="remove">
<xs:anyAttribute processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
<xs:element name="replace">
<xs:complexType>
<xs:complexContent>
<xs:extension base="replace">
<xs:anyAttribute processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
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<xs:any namespace="##other" processContents="lax"/>
</xs:choice>
</xs:sequence>
</xs:choice>
<xs:attribute name="sel" type="xs:anyURI" use="required"/>
<xs:attribute name="new-etag" type="xs:string" use="optional"/>
<xs:attribute name="previous-etag" type="xs:string" use="optional"/>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>
<!-- xcap element type -->
<xs:complexType name="elementType">
<xs:complexContent>
<xs:restriction base="xs:anyType">
<xs:sequence>
<xs:any processContents="lax" namespace="##any"
minOccurs="0" maxOccurs="1"/>
</xs:sequence>
<xs:attribute name="sel" type="xs:string"
use="required"/>
<xs:attribute name="exists" type="xs:boolean"/>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
<!-- xcap attribute type -->
<xs:complexType name="attributeType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="sel" type="xs:string"
use="required"/>
<xs:attribute name="exists" type="xs:boolean"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<!-- empty type -->
<xs:complexType name="emptyType"/>
</xs:schema>
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5. Example Document
The following is an example of a document compliant to the schema.
<?xml version="1.0" encoding="UTF-8"?>
<xcap-diff xmlns="urn:ietf:params:xml:ns:xcap-diff"
xcap-root="http://xcap.example.com/root/">
<document new-etag="7ahggs"
sel="resource-lists/users/sip:joe@example.com/coworkers"
previous-etag="8a77f8d"/>
<d:element sel="rls-services/users/sip:joe@example.com/index/~~
/*/service%5b@uri='sip:marketing@example.com'%5d"
xmlns:d="urn:ietf:params:xml:ns:xcap-diff"
xmlns="urn:ietf:params:xml:ns:rls-services"
xmlns:rl="urn:ietf:params:xml:ns:resource-lists"
><service uri="sip:marketing@example.com">
<list name="marketing">
<rl:entry uri="sip:joe@example.com"/>
<rl:entry uri="sip:sudhir@example.com"/>
</list>
<packages>
<package>presence</package>
</packages>
</service></d:element>
<attribute
sel="rls-services/users/sip:joe@example.com/index/~~/*/service/@uri"
>sip:marketing@example.com</attribute>
</xcap-diff>
This indicates that the document with URI "http://xcap.example.com/
root/resource-lists/users/sip:joe@example.com/coworkers" has changed.
Its previous entity tag is "8a77f8d" and its new one is "7ahggs" but
actual changes are not shown. The <service> element exists in the
rls-services "index" document and its full content is shown. Note
that the <service> element is attached with a default namespace
declaration within the original document. Similarly, a "uri"
attribute content is shown from the same "index" document as an
illustrative example.
6. Security Considerations
XCAP diff documents can include changes from one document to another.
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As a consequence, if the document itself is sensitive and requires
confidentiality, integrity or authentication, then the same applies
to the XCAP diff format. Therefore, protocols which transport XCAP
diff documents must provide sufficient security capabilities for
transporting the document itself.
7. IANA Considerations
There are several IANA considerations associated with this
specification.
7.1. application/xcap-diff+xml MIME Type
MIME media type name: application
MIME subtype name: xcap-diff+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 6 of RFCXXXX [[NOTE TO RFC-EDITOR/IANA: Please replace
XXXX with the RFC number of this specification.]].
Interoperability considerations: none.
Published specification: This document.
Applications which use this media type: This document type has
been used to support manipulation of resource lists [14] using
XCAP.
Additional Information:
Magic Number: None
File Extension: .xdf
Macintosh file type code: "TEXT"
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Personal and email address for further information: Jonathan
Rosenberg, jdrosen@jdrosen.net
Intended usage: COMMON
Author/Change controller: The IETF.
7.2. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:xcap-diff
This section registers a new XML namespace, as per the guidelines in
[7]
URI: The URI for this namespace is
urn:ietf:params:xml:ns:xcap-diff.
Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
Jonathan Rosenberg (jdrosen@jdrosen.net).
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>XCAP Diff Namespace</title>
</head>
<body>
<h1>Namespace for XCAP Diff</h1>
<h2>urn:ietf:params:xml:ns:xcap-diff</h2>
<p>See <a href="[URL of published RFC]">RFCXXXX[[NOTE
TO IANA/RFC-EDITOR: Please replace XXXX with the RFC number of this
specification.]]</a>.</p>
</body>
</html>
END
7.3. Schema Registration
This section registers a new XML schema per the procedures in [7].
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URI: urn:ietf:params:xml:schema:xcap-diff
Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
Jonathan Rosenberg (jdrosen@jdrosen.net).
The XML for this schema can be found as the sole content of
Section 4.
8. Acknowledgments
The authors would like to thank Pavel Dostal, Jeroen van Bemmel,
Martin Hynar and Anders Lindgren for their valuable comments.
9. References
9.1. Normative References
[1] "Canonical XML 1.0", W3C Recommendation REC-xml-c14n-20010315 ,
March 2001.
[2] "Extensible Markup Language (XML) 1.0 (Fourth Edition)", W3C
Recommendation REC-xml-20060816 , August 2006.
[3] "Namespaces in XML (Second Edition)", W3C Recommendation REC-
xml-names-20060816 , August 2006.
[4] Moats, R., "URN syntax", RFC 2141, May 1997.
[5] Murata, M., "XML media types", RFC 3023, January 2001.
[6] Moats, R., "A URN namespace for IETF documents", RFC 2648,
Aug. 1999.
[7] Mealling, M., "The IETF XML Registry", RFC 3688, BCP 81,
January 2004.
[8] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[9] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)", RFC 4825, May 2007.
[10] Urpalainen, J., "An Extensible Markup Language (XML) Patch
Operations Framework Utilizing XML Path Language (XPath)
Selectors", draft-ietf-simple-xml-patch-ops-03, August 2007.
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9.2. Informative References
[11] 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.
[12] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[13] Roach, A., Campbell, B., and J. Rosenberg, "A Session
Initiation Protocol (SIP) Event Notification Extension for
Resource Lists", RFC 4662, August 2006.
[14] Rosenberg, J., "Extensible Markup Language (XML) Formats for
Representing Resource Lists", RFC 4826, May 2007.
[15] Burger, E., Ed., "A Mechanism for Content Indirection in
Session Initiation Protocol (SIP) Messages", RFC 4483,
May 2006.
Authors' Addresses
Jonathan Rosenberg
Cisco
Edison, NJ
US
Email: jdrosen@cisco.com
URI: http://www.jdrosen.net
Jari Urpalainen
Nokia
Itamerenkatu 11-13
Helsinki 00180
Finland
Phone: +358 7180 37686
Email: jari.urpalainen@nokia.com
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