Network Working Group                                       J. Rosenberg
Request for Comments: 4479                                 Cisco Systems
Category: Standards Track                                      July 2006


                       A Data Model for Presence

Status of This Memo

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

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines the underlying presence data model used by
   Session Initiation Protocol (SIP) for Instant Messaging and Presence
   Leveraging Extensions (SIMPLE) presence agents.  The data model
   provides guidance on how to map various communications systems into
   presence documents in a consistent fashion.

























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Table of Contents

   1. Introduction ....................................................2
   2. Definitions .....................................................3
   3. The Model .......................................................5
      3.1. Presentity URI .............................................6
      3.2. Person .....................................................7
      3.3. Service ....................................................8
           3.3.1. Characteristics .....................................9
           3.3.2. Reach Information ..................................10
           3.3.3. Relative Information ...............................13
           3.3.4. Status .............................................13
      3.4. Device ....................................................15
      3.5. Modeling Ambiguity ........................................17
      3.6. The Meaning of Nothing ....................................19
      3.7. Status vs. Characteristics ................................19
      3.8. Presence Document Properties ..............................20
   4. Motivation for the Model .......................................21
   5. Encoding .......................................................22
      5.1. XML Schemas ...............................................24
           5.1.1. Common Schema ......................................24
           5.1.2. Data Model .........................................25
   6. Extending the Presence Model ...................................26
   7. Example Presence Document ......................................26
      7.1. Basic IM Client ...........................................27
   8. Security Considerations ........................................29
   9. Internationalization Considerations ............................29
   10. IANA Considerations ...........................................30
      10.1. URN Sub-Namespace Registration ...........................30
      10.2. XML Schema Registrations .................................31
           10.2.1. Common Schema .....................................31
           10.2.2. Data Model ........................................31
   11. Acknowledgements ..............................................31
   12. References ....................................................32
      12.1. Normative References .....................................32
      12.2. Informative References ...................................32

1.  Introduction

   Presence conveys the ability and willingness of a user to communicate
   across a set of devices.  RFC 2778 [10] defines a model and
   terminology for describing systems that provide presence information.
   RFC 3863 [1] defines an XML [5] [6] [7] document format for
   representing presence information.  In these specifications, presence
   information is modeled as a series of tuples, each of which contains
   a status, communications address, and other markup.  However, neither
   specification gives guidance on exactly what a tuple is meant to
   model, or how to map real-world communications systems (and in



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   particular, those built around the Session Initiation Protocol (SIP)
   [11]) into a presence document.

   In particular, several important concepts are not clearly modeled or
   well delineated by RFCs 2778 and 3863.  These are the following:

   Service:  A communications service, such as instant messaging (IM) or
      telephony, is a system for interaction between users that provides
      certain modalities or content.

   Device:  A communications device is a physical component that a user
      interacts with in order to make or receive communications.
      Examples are a phone, PDA, or PC.

   Person:  A person is the end user, and for the purposes of presence,
      is characterized by states, such as "busy" or "sad", that impact
      their ability and willingness to communicate.

   This specification defines these concepts more fully by means of a
   presence data model, and concretely defines how to take real-world
   systems and map them into presence documents using that model.  This
   data model is defined in terms of an extension to RFC 3863.

2.  Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [9].

   This document makes use of many additional terms beyond those defined
   in RFC 2778 and RFC 3863.  These new terms are as follows:

   Device:  A device models the physical environment in which services
      manifest themselves for users.  Devices have characteristics that
      are useful in allowing a user to make a choice about which
      communications service to use.

   Service:  A service models a form of communication that can be used
      to interact with the user.

   Person:  A person models the human user and their states that are
      relevant to presence systems.

   Occurrence:  A single description of a particular service, a
      particular device, or a person.  There may be multiple occurrences
      for a particular service or device, or multiple person occurrences
      in a Presence Information Data Format (PIDF) document, in cases
      where there is ambiguity that is best resolved by the watcher.



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   Presentity:  A presentity combines devices, services, and person
      information for a complete picture of a user's presence status on
      the network.

   Presentity URI:  A URI that acts as a unique identifier for a
      presentity and provides a handle for obtaining presence
      information about that presentity.

   Data Component:  One of the device, service, or person parts of a
      presence document.

   Status:  Presence information about a service, person, or device that
      typically changes over time, in contrast to characteristics, which
      are generally static.

   Characteristics:  Presence information about a service, person, or
      device that is usually fixed over time, and descriptive in nature.
      Characteristics are useful in providing context that identifies
      the service or device as different from another service or device.

   Attribute:  A status or characteristic.  It represents a single piece
      of presence information.

   Presence Attribute:  A synonym for attribute.

   Composition:  The act of combining a set of presence and event data
      about a presentity into a coherent picture of the state of that
      presentity.























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3.  The Model

    +----------------------------------------------------------------+
    |                                                                |
    |                       +----------------+                       |
    |                      +----------------+|                       |
    |                      |                ||                       |
    |                      |                ||                       |
    |                      |     Person     ||                       |
    |                      |                ||\                      |
    |                     /|                |+ \                     |
    |                    / +----------------+   \                    |
    |                   /           |            \                   |
    |                  /            |             \                  |
    |                 /             |              \                 |
    |                /              |               \                |
    |               /               |                \               |
    |              V                V                 V              |
    |  +----------------+   +----------------+   +----------------+  |
    | +----------------+|  +----------------+|  +----------------+|  |
    | |                ||  |                ||  |                ||  |
    | |                ||  |                ||  |                ||  |
    | |    Service     ||  |    Service     ||  |    Service     ||  |
    | |                ||  |                ||  |                ||  |
    | |                |+  |                |+  |                |+  |
    | +----------------+   +----------------+   +----------------+   |
    |             \              /       \                           |
    |              \            /         \                          |