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Versions: 00 01 02 03 04 05 06 07 08 RFC 3863
Network Working Group H. Sugano
INTERNET-DRAFT S. Fujimoto
Fujitsu
G. Klyne
Baltimore Technologies
A. Bateman
VisionTech
W. Carr
Intel
J. Peterson
NeuStar
Expires: April 2003 October 2002
Common Presence and Instant Messaging (CPIM)
Presence Information Data Format
<draft-ietf-impp-cpim-pidf-06.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Please send comments to the authors or to the impp@iastate.edu
discussion list.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
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Abstract
This memo specifies the Common Presence and Instant Messaging (CPIM)
Presence Information Data Format (PIDF) as a common presence data
format for CPIM-compliant Instant Messaging and Presence protocols,
and also defines a new media type "application/cpim-pidf+xml" to
represent the XML MIME entity for PIDF.
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Table of Content
1. Introduction ......................................... 4
1.1. Terminology and Conventions .......................... 4
2. Design Decisions ..................................... 5
2.1. Minimal Model ........................................ 5
2.2. Added Features ....................................... 6
2.3. XML Encoding Decision ................................ 6
3. Overview of Presence Information Data Format ......... 7
3.1. The 'application/cpim-pidf+xml' Content Type ......... 7
3.2. Presence Information Contents ........................ 7
4. XML-encoded Presence Data Format ..................... 7
4.1. XML Format Definitions ............................... 8
4.1.1. The <presence> element ............................... 8
4.1.2. The <tuple> element .................................. 8
4.1.3. The <status> element ................................. 9
4.1.4. The <basic> element .................................. 10
4.1.5. The <contact> element ................................ 10
4.1.6. The <note> element ................................... 10
4.1.7. The <timestamp> element .............................. 11
4.2. Presence Information Extensibility ................... 11
4.2.1. XML Namespaces Background ............................ 11
4.2.2. XML Namespaces In Presence Information ............... 12
4.2.3. Handling Of Unrecognized Element Names ............... 13
4.2.4. Status Value Extensibility ........................... 14
4.2.5. Standardizing Status Extensions ...................... 14
4.3. Examples ............................................. 16
4.3.1. Default Namespace with Status Extensions ............. 16
4.3.2. Presence with Other Extension Elements ............... 16
4.3.3. Example Mandatory To Understand Elements ............. 17
4.4. XML Schema Definitions ............................... 17
5. IANA Considerations .................................. 19
5.1. Content-type registration for
'application/cpim-pidf+xml' .................. 20
5.2. URN sub-namespace registration for
'urn:ietf:params:xml:ns:cpim-pidf' ........... 21
5.3. URN sub-namespace registration for
'urn:ietf:params:xml:ns:cpim-pidf:status' .... 22
6. Security Considerations .............................. 22
7. Internationalization Considerations .................. 23
8. Normative References ................................. 23
9. Informative References ............................... 24
10. Authors' Addresses .................................. 25
11. Appendix A. Document Type Definitions ............... 26
12. Full Copyright Statement ............................ 27
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1. Introduction
The Common Profile for Instant Messaging (CPIM) specifications define
a set of common operations and various formats to achieve
interoperability between different Instant Messaging and Presence
protocols which meet RFC 2779 [RFC2779]. The CPIM core specification
[CPIM] defines a set of common operations and their parameters to be
supported by interworking Presence and IM protocols in order to allow
straightforward gatewaying between them. The CPIM Message Format
[CPIM-MSG] defines a common format for instant messages, which
enables secure end-to-end IM exchange through the gateways.
This memo further defines the CPIM Presence Information Data Format
(PIDF) as a common presence data format for CPIM-compliant presence
protocols. The significance of the common presence format primarily
resides in the fact that it alleviates the load of gatewaying of
messages with presence data payloads. Without such a common presence
data format, a gateway must process and transform the presence data
payload from one format to another every time it gateways the
protocol messages. Such payload processing also disables the
validity of digitally signed presence data. Utilizing the common
presence data format allows secure transfer of the presence payloads
across the boundary of different protocol domains.
The format specified in this memo is intended to define the base
presence format and extensibility required by RFC 2779. It only
defines a minimal set of presence status values defined by the IMPP
Model document [RFC2778]. However, a presence application is able to
define its own status values using the extensibility framework
provided by this memo. Defining such extended status values is
beyond the scope of this memo.
Note also that this memo defines only the format for a presence data
payload and the extensibility framework for it. How the presence data
is transferred within a specific protocol frame would be defined
separately in a protocol specification.
1.1. Terminology and Conventions
This memo makes use of the vocabulary defined in the IMPP Model
document [RFC2778]. Terms such as CLOSED, INSTANT MESSAGE, OPEN,
PRESENCE SERVICE, PRESENTITY, WATCHER, and WATCHER USER AGENT in the
memo are used in the same meaning as defined therein.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in RFC 2119 [RFC2119].
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[[[Editorial comments and questions about outstanding issues are
provided in triple brackets like this. These working comments should
be resolved and removed prior to final publication.]]]
2. Design Decisions
We have adopted the IMPP Model and Requirements documents [RFC2778,
RFC2779] as the starting point of our discussion. The two RFCs
contains a number of statements about presence information, which can
be regarded as a basic set of constraints for the format design.
Also, we took the minimalist approach to the design based on them.
Starting from the minimal model, only the features that are necessary
to solve particular problems have been combined.
2.1. Minimal Model
This specification is based on the minimal model extracted from the
IMPP Model and Requirements documents. The model consists of the
following items. Each of them is accompanied with the corresponding
RFCs and their section numbers as its grounds, e.g. (RFC2778:Sec.2.4)
refers to Section 2.4 of RFC 2778.
(a) PRESENCE INFORMATION consists of one or more PRESENCE TUPLES,
where a PRESENCE TUPLE consists of a STATUS, an optional
COMMUNICATION ADDRESS, and optional OTHER PRESENCE MARKUP.
Note that the CONTACT ADDRESS in a COMMUNICATIONS ADDRESS is
understood more narrowly in this document to refer only to a
URI. (RFC2778:Sec.3)
(b) STATUS has at least the mutually-exclusive values OPEN and
CLOSED, which have meaning for the acceptance of INSTANT
MESSAGES, and may have meaning for other COMMUNICATION MEANS.
There may be other values of STATUS that do not imply anything
about INSTANT MESSAGE acceptance. These other values of STATUS
may be combined with OPEN and CLOSED or they may be mutually-
exclusive with those values. (RFC2778:Sec.3, RFC2779:Sec.4.4.1-
4.4.3)
(c) STATUS may consist of single or multiple values. (RFC2778:Sec.2.4)
(d) There must be a means of extending the common presence format
to represent additional information not included in the common
format. The extension and registration mechanisms must be
defined for presence information schema, including new STATUS
conditions and new forms for OTHER PRESENCE MARKUP. (RFC2779:
Sec.3.1.4-3.1.5)
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(e) The common presence format must include a means to uniquely
identify the PRESENTITY whose PRESENCE INFORMATION is reported.
(RFC2779:Sec.3.1.2)
(f) The common presence format must allow the PRESENTITY to secure
presence information sent to a WATCHER. The format must allow
integrity, confidentiality and authentication properties to be
applied to presence information. (RFC2779:Sec5.2.1, 5.2.4, 5.3.1,
5.3.3)
2.2. Added Features
In addition to the minimal model described above, the format
specified in this specification has the following features.
(a) Relative priorities of contact addresses should be specifiable
in order to allow the source of PRESENCE INFORMATION to tell the
receiver (WATCHER USER AGENTS) its preference over multiple contact
means.
(b) The presence format should be able to contain the timestamp of
the creation of the PRESENCE INFORMATION. The timestamp in the
presence document lets the receiver know the time of the creation
of the data even if the message containing it arrives late for
some reason. It can also be used to detect a replay attack,
independent of the underlying signature mechanism. Note that
this mechanism does not assume any global time synchronization
system for watchers and presentities (see Appendix A of RFC2779,
8.1.4 A7), but rather assumes that the minimum length of time
that might pass before presence information is considered stale
is long enough that minor variations among system clocks will not
lead to misjudgments of the freshness of presence information."
2.3. XML Encoding Decision
The CPIM Presence Information Data Format encodes presence
information in XML (eXtensible Markup Language [XML]), which is
rapidly gaining broad acceptance as a syntactic framework to encode
structured data transferred over the Internet. Regarding the
features of PRESENCE INFORMATION discussed above, such that it has a
hierarchical structure and it should be fully extensible, XML is
considered as the most desirable framework over other candidates such
as vCard [RFC2426].
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3. Overview of Presence Information Data Format
This section describes an overview of the presence data format
defined in this memo.
3.1. The 'application/cpim-pidf+xml' Content Type
This memo defines a new content type "application/cpim-pidf+xml" for
an XML MIME entity that encodes presence information conformant to
this specification. This specification follows the recommendations
and conventions described in [RFC3023], including the naming
convention of the type ('+xml' suffix) and the usage of the 'charset'
parameter.
Although it is defined as optional, use of the 'charset' parameter is
STRONGLY RECOMMENDED. If the 'charset' parameter is not specified,
conforming XML processors to [XML] MUST follow the requirements in
section 4.3.3 of [XML].
3.2. Presence Information Contents
This subsection outlines the information in an "application/cpim-
pidf+xml" document. A full definition of the PIDF content is in
Section 4.
o PRESENTITY URL: specifies the "pres" URL of the PRESENTITY.
o List of presence tuples
- Status: OPEN/CLOSED for Instant Messaging or status for
other communication means.
- Communication address: communication means and contact
address of this tuple. (optional)
- Relative priority: numerical value specifying the priority
of this communication address. (optional)
- Timestamp: timestamp of the change of this tuple.(optional)
- Human readable comment: free text memo about this tuple
(optional)
o PRESENTITY human readable comment: free text memo about the
PRESENTITY (optional).
4. XML-encoded Presence Data Format
This section defines an XML-encoded presence information data format
(PIDF) for use with CPIM compliant systems. A presence payload in
this format is expected to be produced by the PRESENTITY (the source
of the PRESENCE INFORMATION) and transported to the WATCHERS by the
presence servers or gateways without any interpretation or
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modification.
4.1. XML Format Definitions
A PIDF object is a well formed XML document.
It MUST have the XML declaration and it SHOULD contain an encoding
declaration in the XML declaration, e.g. "<?XML version='1.0'
encoding='UTF-8'?>". If the charset parameter of the MIME content
type declaration is present and it is different from the encoding
declaration, the charset parameter takes precedence.
Every application conformant to this specification MUST accept the
UTF-8 character encoding to ensure the minimal interoperability.
4.1.1. The <presence> element
The root element of the "application/cpim-pidf+xml" object is defined
as <presence>. This element contains one or more <tuple> elements,
followed by any number (including 0) of OPTIONAL <note> elements,
followed by any number of OPTIONAL extension elements from other
namespaces.
The <presence> element MUST have an 'entity' attribute. The value of
the 'entity' attribute is the 'pres' URL of the PRESENTITY publishing
this presence document.
The <presence> element MUST contain a namespace declaration ('xmlns')
to indicate the namespace on which the presence document is based.
The presence document compliant to this specification MUST have the
namespace 'urn:ietf:params:xml:ns:cpim-pidf:'.
It MAY contain other namespace declarations for the extensions used
in the presence XML document.
4.1.2. The <tuple> element
The <tuple> element is used to carry a piece of PRESENCE INFORMATION
defined as PRESENCE TUPLE in RFC2778. Thus, it contains one
mandatory <status> element, followed by any number of OPTIONAL
extension elements from other namespaces, followed by one OPTIONAL
<contact> elements, followed by any number of OPTIONAL <note>
elements, followed by one OPTIONAL <timestamp> elements.
Tuples provide a way of segmenting presence information. Protocols or
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applications may choose to segment the presence information
associated with a presentity for any number of reasons - for example,
because components of the full presence information for a presentity
have come from distinct devices or different applications on the same
device, or have been generated at different times. Tuples should be
preferred over other manners of segmenting presence information such
as creating multiple PIDF instances.
The <tuple> element MUST contain an 'id' attribute which is used to
distinguish this tuple from other tuples in the same XML document.
The value of an 'id' attribute MUST be unique within 'id' attribute
values of other tuples in the same document. An 'id' value is used
by applications processing the presence document to identify the
corresponding tuple in the previously acquired PRESENCE INFORMATION
of the same PRESENTITY. The value of the 'id' attribute SHOULD be
treated as just a CDATA value (no semantics).
The <contact> element is OPTIONAL because a PRESENTITY might need to
hide its COMMUNICATION ADDRESS or there might be tuples not related
to any COMMUNICATION MEANS. Tuples that contain a <basic> status
element SHOULD contain a <contact> address. Tuples MAY contain
conflicting presence status - one <tuple> might provide a <basic>
<status> of OPEN, and another <tuple> in the same PIDF could contain
a <basic> <status> of CLOSED, even if they both contain the same
<contact> address.
The manner in which segmented presence information is understood by
the WATCHER USER AGENT is highly dependent on the capabilities of the
WATCHER USER AGENT and the presence application in question. In the
absence of any application-specific or protocol-specific
understanding of the meaning of tuples, WATCHER USER AGENTS MAY obey
the following guidelines. WATCHER USER AGENTS should note which
tuples in the PIDF have changed their state since the last
notification by correlating the 'id' of each <tuple> with those
received in previous notifications and comparing both <status> values
and <timestamp> elements in the tuples, if any are present.
4.1.3. The <status> element
The <status> element contains one OPTIONAL <basic> elements, followed
by any number of OPTIONAL extension elements from other namespaces,
under the restriction that at least one child element appears in the
<status> element. These children elements of <status> contain status
values of this tuple. By allowing multiple status values in a single
<tuple> element, different types of status values, e.g. reachability
and location, can be represented by a <tuple>. See Section 4.3 for an
example with multiple status values.
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This memo only defines the <basic> status value element. Other status
values may be included using the standard extensibility framework
(see Section 4.2.4). Applications encountering unrecognized elements
within <status> may ignore them, unless they carry a
mustUnderstand="true" or mustUnderstand="1" attribute (see section
4.2.3).
Note that, while the <status> element MUST have at least one status
value element, this status value may not be the <basic> element.
4.1.4. The <basic> element
The <basic> element contains one of the following strings: "open" or
"closed". The values "open" and "closed" has the same meaning as
OPEN and CLOSED defined in RFC 2778 respectively, and stand for
availability of receiving instant messages if the <tuple> is for an
instant messaging address. They also have meanings of general
availability for other communication means. But, this memo does not
specify them in detail.
4.1.5. The <contact> element
The <contact> element contains a URL of the contact address. It
optionally has a 'priority' attribute, whose value means a relative
priority of this contact address over the others. The value of the
attribute MUST be a decimal number between 0 and 1 inclusive with at
most 3 digits after the decimal point. Higher values indicate higher
priority. Examples of priority values are 0, 0.021, 0.5, 1.00. If the
'priority' attribute is omitted, applications MUST understand that
the contact address has the lowest priority. If the 'priority' value
is out of the range, applications just SHOULD ignore the value and
process it as if the attribute was not present.
It is RECOMMENDED that applications handles a contact with higher
priority than another one so that the priority is recognizable by
users. How to handle contacts with the same priority is up to
implementations.
4.1.6. The <note> element
The <note> element contains a string value, which is usually used for
a human readable comment. A <note> element MAY appear as a child
element of <presence> or as a child element of the <tuple> element.
In the former case, the comment is about the PRESENTITY and, in the
latter case, the comment is regarding the particular tuple.
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The <note> element SHOULD have a special attribute 'xml:lang' to
specify the language used in the contents of this element as defined
in Section 2.12 of [XML]. The value of this attribute is the
language indentifier as defined by [RFC1766]. It MAY be omitted when
the language used is implied by the larger context such as the
encoding information of the contents, such as an xml:lang attribute
on an enclosing XML element, or a Content-language header [RFC3282]
on an enclosing MIME wrapper.
4.1.7. The <timestamp> element
The <timestamp> element contains a string indicating the date and
time of the status change of this tuple. The value of this element
MUST follow the IMPP datetime format [RFC3339]. Timestamps that
contain 'T' or 'Z' MUST use the capitalized forms.
As a security measure, the <timestamp> element SHOULD be included in
all tuples unless the exact time of the status change cannot be
determined. For security guidelines for watchers receiving presence
information with timestamps, see the Security Considerations.
4.2. Presence Information Extensibility
The presence information extensibility framework is based on XML
namespaces [XML-NS].
RFC2779 requires that PIDF have a means of extending <status> values
beyond <basic>. These extensions MUST NOT modify how <basic> is to be
understood, nor change the the structure or semantics of PIDF bodies
themselves. These extensions merely allow protocols and applications
to define richer presence data.
4.2.1. XML Namespaces Background
All elements and some attributes are associated with a "namespace",
which is in turn associated with a globally unique URI. Any
developer can introduce their own element names, avoiding conflict by
choosing an appropriate namespace URI.
Within the presence data, element or attribute names are associated
with a particular namespace by a namespace prefix, which is a leading
part of the name, followed by a colon (":"); e.g.
<prefix:element-name ...> ... </prefix:element-name>
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Where, 'prefix' is the header name prefix, 'element-name' is a name
which is scoped by the namespace associated with 'prefix'. Note that
the choice of 'prefix' is quite arbitrary; it is the corresponding
URI that defines the naming scope. Two different prefixes associated
with the same namespace URI refer to the same namespace.
A default namespace can be declared for XML elements without a
namespace prefix. The default namespace does NOT apply to attribute
names, but interpretation of an unprefixed attribute can be
determined by the containing element.
A namespace is identified by a URI. In this usage, the URI is used
simply as a globally unique identifier, and there is no requirement
that it can be used to retrieve a web resource, or for any other
purpose. Any legal globally unique URI MAY be used to identify a
namespace. (By "globally unique", we mean constructed according to
some set of rules so that it is reasonable to expect that nobody else
will use the same URI for a different purpose.)
For further details, see the XML namespace specification [XML-NS].
4.2.2. XML Namespaces In Presence Information
A URI used as a namespace identifier in PRESENCE INFORMATION data
MUST be a full absolute-URI, per RFC 2396 [URI]. (Relative URIs and
URI- references containing fragment identifiers MUST NOT be used for
this purpose.)
The namespace URI for elements defined by this specification is a URN
[URN], using the namespace identifier 'ietf' defined by [URN-NS-IETF]
and extended by [XML-Registry]:
urn:ietf:params:xml:ns:cpim-pidf
Thus, simple presence data might be thus:
<?xml version="1.0" encoding="UTF-8"?>
<impp:presence xmlns:impp="urn:ietf:params:xml:ns:cpim-pidf"
entity="pres:someone@example.com">
<impp:tuple id="sg89ae">
<impp:status>
<impp:basic>open</impp:basic>
</impp:status>
<impp:contact priority="0.8">tel:09012345678</impp:contact>
</impp:tuple>
</impp:presence>
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or, using a default XML namespace:
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
entity="pres:someone@example.com">
<tuple id="sg89ae">
<status>
<basic>open</basic>
</status>
<contact priority="0.8">tel:09012345678</contact>
</tuple>
</presence>
As is generally the case in XML, the xmlns attribute can be used on
any element in the presence information to define either the default
namespace or a namespace associated with a namespace prefix.
4.2.3. Handling Of Unrecognized Element Names
Except as noted below, a processor of PRESENCE INFORMATION MUST
ignore any XML element with an unrecognized name (i.e. having an
unrecognized namespace URI, or an unrecognized local name within that
namespace). This includes all of the element content, even if it
appears to use recognized names.
Extensions to PIDF are informational in nature - they provide
additional information beyond <basic> status. However, in order to
understand a complex extension, nested elements within an extension
element might need to be marked as mandatory. In such cases, the
element name is qualified with a mustUnderstand='true' or
mustUnderstand='1' attribute, which attribute name is associated with
the CPIM presence namespace.See section 4.3.3 for an example.
NOTE: a mustUnderstand='true' or mustUnderstand='1' attribute
within an element that is being ignored is itself ignored. The
writer of nested mandatory-to-understand information is responsible
for ensuring that any enclosing element is also labelled with a
mustUnderstand='true' or mustUnderstand='1' attribute, if
necessary.
This specification defines (section 4.1) elements within the
'urn:ietf:params:xml:ns:cpim-pidf' namespace that MUST be recognized
in CPIM presence data. Processors MUST handle these as described,
even if they do not carry a mustUnderstand attribute. The XML Schema
Definition (section 4.4) indicates those elements that MUST be
present in a valid presence information document.
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If an agent receives PRESENCE INFORMATION with a <status> block
containing an unrecognized element that has a mustUnderstand='true'
(or '1') attribute, it should treat the entire element as
unrecognized and not attempt to process it.
Note that the mustUnderstand attribute MUST NOT be used in a way that
might prevent a minimal implementation from understanding the basic
PIDF information defined in this specification. To ensure this, the
mustUnderstand attribute MUST NOT be used outside elements within
optional, so that non-recognition of a mandatory extension results in
no worse than ignoring the optional extension in which it is
contained.
4.2.4. Status Value Extensibility
This memo only defines the <basic> status value with values of "open"
and "closed". Other status values are possible using the standard
namespace-based extensibility rules defined above.
For example, a location status value might be included thus:
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:local="urn:example-com:pidf-status-type"
entity="pres:someone@example.com">
<tuple id="938s3w">
<status>
<basic>open</basic>
<local:location>home</local:location>
</status>
<contact>im:someone@example.com</contact>
</tuple>
</presence>
Some new status values will 'extend' the value of the <basic>
element. For example, a status value defined for use with instant
messaging may include values such as 'away', 'busy' and 'offline'. In
order that some level of interoperability be maintained with user
agents that don't recognise the new extension, the <basic> status
value must also be included. This means that extensions are not
obligated to define a mapping from each of their values to OPEN or
CLOSED.
4.2.5. Standardizing Status Extensions
Although the existing PIDF definition allows arbitrary elements to
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appear in the <status> element, it may be sometimes desirable to
standardize extension status elements and their semantics (the
meanings of particular statuses, how their should be interpreted).
The URN 'urn:ietf:params:xml:ns:cpim-pidf:status' has been defined as
a namespace URI for extensions standardized by the IETF, and new
values in this namespace must be defined by a standards-track RFC.
The following example XML Schema defines an extension for <location>
presence information, which can have the values of 'home', 'office',
or 'car'. If the <location> element were standardized, this document
would be made available in an RFC along with information about the
use of the extension. These extensions should use the namespace
'urn:ietf:params:xml:ns:cpim-pidf:status', and each RFC defining an
extension should register an extension name within that namespace
with IANA.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:cpim-pidf:status"
xmlns:tns="urn:ietf:params:xml:ns:cpim-pidf:status"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xs:simpleType name="location">
<xs:restriction base="xs:string">
<xs:enumeration value="home"/>
<xs:enumeration value="office"/>
<xs:enumeration value="car"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
In addition to the XML Schema to validate the extension, registration
of the extension name with IANA, RFCs defining extensions MUST
discuss:
- The domain of applicability of the extension. Is this extension
exclusively valuable to IM clients, telephones, geolocators, etc?
What sorts of presence applications would use this extension and
under what circumstances?
- Semantics for the presence states defined in the extension. What
disposition provokes an automated presentity to declare that it is
in state X, or does a human select X from a drag-down menu? Is
there any general guidance for watchers of presence information
with state Y (for example, how they should best attempt to
communicate with the presentity, if at all, when the principal is
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in state Y).
Extensions SHOULD also discuss:
- How, if at all, any presence states defined in the extension
related to <basic>, or to any relevant extension previously
published in an RFC. For example, "state Z implies OPEN, so it MUST
NOT be used if a basic state of CLOSED is expressed", or "you
should use the extension in this document, not the extension in RFC
QQQQ, if your circumstances are as follows...."
4.3. Examples
4.3.1. Default Namespace with Status Extensions
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:im="urn:ietf:params:xml:ns:cpim-pidf:im"
xmlns:myex="http://id.example.com/cpim-presence/"
entity="pres:someone@example.com">
<tuple id="35bs9r">
<status>
<basic>open</basic>
<im:im>busy</im:im>
<myex:location>home</myex:location>
</status>
<contact priority="0.8">im:someone@mobilecarrier.net</contact>
<note xml:lang="en">Don't Disturb Please!</note>
<note xml:lang="fr">Ne derangez pas, s'il vous plait</note>
<timestamp>2001-10-27T16:49:29Z</timestamp>
</tuple>
<tuple id="8eg92n">
<status>
<basic>open</basic>
</status>
<contact priority="1.0">mailto:someone@example.com</contact>
</tuple>
<note>I'll be in Tokyo next week</note>
</presence>
4.3.2. Presence with Other Extension Elements
<?xml version="1.0" encoding="UTF-8"?>
<impp:presence xmlns:impp="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:myex="http://id.example.com/cpim-presence/"
entity="pres:someone@example.com">
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<impp:tuple id="c38g92">
<impp:status>
<impp:basic>open</impp:basic>
</impp:status>
<myex:mytupleelement>Extended value in tuple</myex:mytupleelement>
<impp:contact priority="0.65">tel:09012345678</impp:contact>
</impp:tuple>
<impp:tuple id="71md66">
<impp:status>
<impp:basic>open</impp:basic>
</impp:status>
<impp:contact priority="1.0">
im:someone@mobilecarrier.net</impp:contact>
</impp:tuple>
<myex:mytag>My extended presentity information</myex:mytag>
</impp:presence>
4.3.3. Example Mandatory To Understand Elements
<?xml version="1.0" encoding="UTF-8"?>
<impp:presence xmlns:impp="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:myex="http://id.mycompany.com/cpim-presence/"
entity="pres:someone@example.com">
<impp:tuple id="t6j2ds">
<impp:status>
<impp:basic>open</impp:basic>
</impp:status>
<myex:complexExtension>
<myex:ex1 impp:mustUnderstand="1">val1</myex:ex1>
<myex:ex2>val2</myex:ex2>
</myex:complexExtension>
<impp:contact priority="0.725">tel:09012345678</impp:contact>
</impp:tuple>
<myex:mytag>My extended presentity information</myex:mytag>
</impp:presence>
Here, <myex:ex1> must be understood and, if it is not recognized,
<myex:complexExtension> MUST be ignored. <myex:mytag> and
<myex:ex2> MAY be ignored if they are not recognized.
4.4. XML Schema Definitions
This section gives the XML Schema Definition [XMLSchema1] of the
"application/cpim-pidf+xml" format. This is presented as a formal
definition of the "application/cpim-pidf+xml" format. Note that the
XML Schema definition is not intended to be used with on-the-fly
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validation of the presence XML document.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:tns="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- This import brings in the XML language attribute xml:lang-->
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:element name="presence" type="tns:presence"/>
<xs:complexType name="presence">
<xs:sequence>
<xs:element name="tuple" type="tns:tuple"
maxOccurs="unbounded"/>
<xs:element name="note" type="tns:note" minOccurs="0"
maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="entity" type="xs:anyURI" use="required"/>
</xs:complexType>
<xs:complexType name="tuple">
<xs:sequence>
<xs:element name="status" type="tns:status"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
<xs:element name="contact" type="tns:contact" minOccurs="0"/>
<xs:element name="note" type="tns:note" minOccurs="0"
maxOccurs="unbounded"/>
<xs:element name="timestamp" type="xs:dateTime" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="id" type="xs:ID" use="required"/>
</xs:complexType>
<xs:complexType name="status">
<xs:sequence>
<xs:element name="basic" type="tns:basic" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
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<xs:simpleType name="basic">
<xs:restriction base="xs:string">
<xs:enumeration value="open"/>
<xs:enumeration value="closed"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="contact">
<xs:simpleContent>
<xs:extension base="xs:anyURI">
<xs:attribute name="priority" type="tns:qvalue"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:complexType name="note">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute ref="xml:lang"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:simpleType name="qvalue">
<xs:restriction base="xs:decimal">
<xs:pattern value="0(.[0-9]{0,3})?"/>
<xs:pattern value="1(.0{0,3})?"/>
</xs:restriction>
</xs:simpleType>
<!-- Global Attributes -->
<xs:attribute name="mustUnderstand" type="xs:boolean" default="0">
<xs:annotation>
<xs:documentation>
This attribute may be used on any element within an optional
PIDF extension to indicate that the corresponding element must
be understood by the PIDF processor if the enclosing optional
element is to be handled.
</xs:documentation>
</xs:annotation>
</xs:attribute>
</xs:schema>
5. IANA Considerations
This memo calls for IANA to:
- register a new MIME content-type application/cpim-pidf+xml,
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per [RFC 2048],
- register a new XML namespace URN per [XML-Registry].
- register a new XML namespace URN for status extensions per
[XML-Registry].
The registration templates for these are below. For more information
on status extensions, see section 4.2.5.
5.1. Content-type registration for 'application/cpim-pidf+xml'
To: ietf-types@iana.org
Subject: Registration of MIME media type application/cpim-pidf+xml
MIME media type name: application
MIME subtype name: cpim-pidf+xml
Required parameters: (none)
Optional parameters: charset
Indicates the character encoding of enclosed XML. Default is UTF-8.
Encoding considerations:
Uses XML, which can employ 8-bit characters, depending on the
character encoding used.
See RFC 3023 [RFC 3023], section 3.2.
Security considerations:
This content type is designed to carry presence data, which may
be considered private information. Appropriate precautions should
be adopted to limit disclosure of this information.
Interoperability considerations:
This content type provides a common format for exchange of presence
information across different CPIM compliant protocols.
Published specification:
RFCXXXX (this document)
Applications which use this media type:
Presence and instant messaging systems.
Additional information:
Magic number(s):
File extension(s):
Macintosh File Type Code(s):
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Person & email address to contact for further information:
Hiroyasu Sugano
E-mail: sugano.h@jp.fujitsu.com
Intended usage:
LIMITED USE
Author/Change controller:
This specification is a work item of the IETF IMPP working group,
with mailing list address <impp@iastate.edu>.
Other information:
This media type is a specialization of application/xml [RFC 3023],
and many of the considerations described there also apply to
application/cpim-pidf+xml.
5.2. URN sub-namespace registration for 'urn:ietf:params:xml:ns:cpim-
pidf'
URI
urn:ietf:params:xml:ns:cpim-pidf
Description:
This is the XML namespace URI for XML elements defined by [RFCXXXX]
to describe CPIM presence information in application/cpim-pidf+xml
content type.
Registrant Contact
IETF, IMPP working group, <impp@iastate.edu>
Hiroyasu Sugano, <sugano.h@jp.fujitsu.com>
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=utf-8"/>
<title>Namespace for CPIM presence information</title>
</head>
<body>
<h1>Namespace for CPIM presence information</h1>
<h2>application/cpim-pidf+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
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</html>
END
5.3. URN sub-namespace registration for 'urn:ietf:params:xml:ns:cpim-
pidf:status'
URI
urn:ietf:params:xml:ns:cpim-pidf:status
Description:
This is the XML namespace URI for XML elements defined by [RFCXXXX]
to describe extensions to the status of CPIM presence information
in application/cpim-pidf+xml content type.
Registrant Contact
IETF, IMPP working group, <impp@iastate.edu>
Hiroyasu Sugano, <sugano.h@jp.fujitsu.com>
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=utf-8"/>
<title>Namespace for CPIM status extensions</title>
</head>
<body>
<h1>Namespace for CPIM presence information extensions</h1>
<h2>application/cpim-pidf+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
6. Security Considerations
Because presence is very privacy-sensitive information, the protocol
for the presence information MUST have capabilities to protect PIDF
from possible threats, such as eavesdropping, corruption, tamper and
replay attacks. These security mechanisms must be able to be used
end-to-end between presentities and watchers, even if the watcher and
the presentity employ different presence protocols and communicate
through a CPIM gateway. Since the 'application/cpim-pidf+xml' MIME
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type is defined for this PIDF document, staging security for PIDF at
the MIME level (with S/MIME [RFC2633]) seems appropriate. Therefore,
PIDF should follow the normaivge recommendations for the use of
S/MIME (including minimum ciphersuites) given in the core CPIM
specification.
Note that the use of timestamps in PIDF (see section 4.1.7) can
provide some rudimentary protection against replay attacks. If a
watcher receives presence information that is outdated, it SHOULD be
ignored. A watcher can determine that presence information is
outdated in a number of fashions. Most significantly, if the newest
timestamp in presence information is older than the newest timestamp
in the last received presence information, it should be considered
outdated. Applications and protocols also are advised to adopt their
own rules for determining how frequently presence information should
be refreshed. For example, if presence information appears to be more
than one hour old, it could be considered outdated (a notification
generated for this presence information will not take such a long
time to reach a watcher, and if a presentity has not refreshed its
presence state in the last hour, it is probably offline).
7. Internationalization Considerations
All the processors conformant to this specification MUST be able to
generate and accept UTF-8 encoding, this being one of the mandatory
character encodings for XML conforming processors, and also required
by the policies set out in RFC 2277 [RFC2277].
Other character encodings MAY be accepted (but CPIM compliant
processors are strongly discouraged from emitting anything other than
UTF-8).
8. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC2778] M. Day, J. Rosenberg, H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[RFC2779] M. Day, S. Aggarwal, G. Mohr, and J. Vincent, "Instant
Messaging / Presence Protocol Requirements", RFC 2779, February 2000.
[RFC3023] M. Murata, S. St.Laurent, D. Kohn, "XML Media Types",
RFC 3023, January 2001.
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[XML] T. Bray, J. Paoli, C. Sperberg-McQueen and E. Maler,
"Extensible Markup Language (XML) 1.0 (Second Edition)",
W3C Recommendation, October 2000,
<http://www.w3.org/TR/2000/REC-xml-20001006>
[MIME] Multipurpose Internet Mail Extensions. See RFC 822, RFC 2045,
RFC 2046, RFC 2047, RFC 2048, and RFC 2049.
[RFC1766] H. Alvestrand, "Tags for the Identification of Languages",
RFC 1766, March 1995.
[RFC3339] G. Klyne and C.Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
[XML-NS] Tim Bray, Dave Hollander, and Andrew Layman "Namespaces in
XML", W3C recommendation: xml-names, 14 January 1999,
<http://www.w3.org/TR/REC-xml-names>
[URI] T. Berners-Lee, R.T.Fielding and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
[URN] R. Moats, "URN Syntax", RFC 2141, May 1997.
[URN-NS-IETF] R. Moats, "A URN Namespace for IETF Documents", RFC
2648, August 1999.
[XML-Registry] M. Mealling, "The IETF XML Registry",
draft-mealling-iana-xmlns-registry-03, Work in Progress.
[RFC2277] H. Alvestrand, "IETF Policy on Character Sets and
Languages", RFC 2277, BCP 18, January 1998.
[XMLSchema1] H. Thompson, D. Beech, M. Maloney and N. Mendelsohn,
"XML Schema Part 1: Structures", W3C REC-xmlschema-1, May 2001,
<http://www.w3.org/TR/xmlschema-1/>.
9. Informative References
[CPIM] D. Crocker et al., "Common Presence and Instant Messaging
(CPIM)", draft-ietf-impp-cpim-02.txt, Work in Progress.
[CPIM-MSG] D. Atkins and G. Klyne, "Common Presence and Instant
Messaging Message Format", draft-ietf-impp-cpim-msgfmt-06.txt,
Work in Progress.
[vCard] F. Dawson and T. Howes, "vCard MIME Directory Profile",
RFC 2426, September 1998.
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[RFC2633] B. Ramsdell, "S/MIME Version 3 Message Specification",
RFC 2633, June 1999.
[RFC3282] H. Alvestrand, "Content Language Headers", RFC 3282,
May 2002.
10. Authors' Addresses
Hiroyasu Sugano
Fujitsu Laboratories Ltd.
64, Nishiwaki
Ohkubo-cho
Akashi 674-8555
Japan
E-mail: sugano.h@jp.fujitsu.com
Shingo Fujimoto
Fujitsu Laboratories Ltd.
64, Nishiwaki
Ohkubo-cho
Akashi 674-8555
Japan
E-mail: shingo_fujimoto@jp.fujitsu.com
Graham Klyne
Clearswift Corporation
1310 Waterside,
Arlington Business Park
Theale
Reading, RG7 4SA
United Kingdom.
Telephone: +44 11 8903 8903
Facsimile: +44 11 8903 9000
E-mail: graham.klyne@clearswift.com
Adrian Bateman
VisionTech Limited
Colton, Staffordshire, WS15 3LD
United Kingdom
E-mail: bateman@acm.org
Wayne Carr
Intel Corporation
2111 NE 25th Avenue
Hillsboro, OR 97124
USA
E-mail: wayne.carr@intel.com
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Jon Peterson
NeuStar, Inc.
1800 Sutter St
Suite 570
Concord, CA 94520
USA
Phone: +1 925/363-8720
E-mail: jon.peterson@neustar.biz
11. Appendix A. Document Type Definitions
The Document Type Definition for the "application/cpim-pidf+xml"
format is described. The DTD here is presented only for
informational for those who may not familiar with the XML Schema
definition.
Note: the DTD does not show where extension elements can be added.
See the XML Schema for that information.
<!ENTITY % URL "CDATA">
<!ENTITY % URI "CDATA">
<!ENTITY % TUPLEID "CDATA">
<!ENTITY % DATETIME "CDATA">
<!ENTITY % VALUETYPE "CDATA">
<!ENTITY % PRIORITY "CDATA">
<!ENTITY % NOTE "CDATA">
<!ELEMENT presence ((tuple+),note?)>
<!ATTLIST presence
xmlns %URI; #REQUIRED
entity %URL; #REQUIRED
>
<!ELEMENT tuple (status,contact?,note?,timestamp?)>
<!ATTLIST tuple
id %TUPLEID; #REQUIRED
>
<!ELEMENT status (basic?)>
<!ELEMENT basic CDATA>
<!ELEMENT contact %URL;>
<!ATTLIST contact
priority %PRIORITY; #IMPLIED
>
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<!ELEMENT note %NOTE;>
<!ELEMENT timestamp %DATETIME;>
12. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS 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.
Sugano et al. [Page 27]
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