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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: June 2003                                        December 2002

              Common Presence and Instant Messaging (CPIM)
                    Presence Information Data Format
                   <draft-ietf-impp-cpim-pidf-07.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 ......................   15
      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 any number (including 0) of
   <tuple> elements, followed by any number (including 0) of <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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   Note that, wherever it appears, a <note> element SHOULD NOT be used,
   and interpreted, as a non-interoperable substitute for status of its
   parent element.

   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



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   part of the name, followed by a colon (":"); e.g.

      <prefix:element-name ...> ... </prefix:element-name>

   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>



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         <impp:contact priority="0.8">tel:09012345678</impp:contact>
       </impp:tuple>
     </impp:presence>

   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,



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   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.

   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.




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4.2.5. Standardizing Status Extensions

   Although the existing PIDF definition allows arbitrary elements to
   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



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     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
     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"?>



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   <impp:presence xmlns:impp="urn:ietf:params:xml:ns:cpim-pidf"
        xmlns:myex="http://id.example.com/cpim-presence/"
        entity="pres:someone@example.com">
     <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



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   "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
   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" minOccurs="0"
            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"/>



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       </xs:sequence>
     </xs:complexType>

     <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



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   This memo calls for IANA to:
      - register a new MIME content-type application/cpim-pidf+xml,
        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):



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     File extension(s):
     Macintosh File Type Code(s):

   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>



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          <h2>application/cpim-pidf+xml</h2>
          <p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
        </body>
        </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



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   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
   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.




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   [RFC3023] M. Murata, S. St.Laurent, D. Kohn, "XML Media Types",
   RFC 3023, January 2001.

   [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.



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   [vCard] F. Dawson and T. Howes, "vCard MIME Directory Profile",
   RFC 2426, September 1998.

   [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



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   Hillsboro, OR 97124
   USA
   E-mail: wayne.carr@intel.com

   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;>



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   <!ATTLIST contact
             priority %PRIORITY; #IMPLIED
   >

   <!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.














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