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Versions: (draft-khartabil-simple-filter-format) 00 01 02 03 04 05 RFC 4661

SIMPLE                                                      H. Khartabil
Internet-Draft                                               E. Leppanen
Expires: August 2, 2004                                      M. Lonnfors
                                                        J. Costa-Requena
                                                                   Nokia
                                                        February 2, 2004


       An Extensible Markup Language (XML) Based Format for Event
                         Notification Filtering
                   draft-ietf-simple-filter-format-00

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.

   This Internet-Draft will expire on August 2, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   The SIP event notification framework describes the usage of the
   Session Initiation Protocol (SIP) for subscriptions and notifications
   of changes to a state of a resource. The document does not describe a
   mechanism of how filtering of event notification information can be
   achieved.

   In order to enable this, a format is needed to enable the subscriber
   to choose when notifications are to be sent to it and what they are
   to contain. This document presents a solution in the form of an XML



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   document format.

Table of Contents

   1.      Conventions  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  3
   3.      Structure of XML-Encoded Filter Criteria . . . . . . . . .  3
   3.1     The <filter-set> Root Element  . . . . . . . . . . . . . .  4
   3.2     The <filter> Element . . . . . . . . . . . . . . . . . . .  4
   3.3     The <what> Element . . . . . . . . . . . . . . . . . . . .  5
   3.3.1   The <include> Element  . . . . . . . . . . . . . . . . . .  5
   3.3.1.1 The "type" Attribute . . . . . . . . . . . . . . . . . . .  6
   3.3.2   The <exclude> Element  . . . . . . . . . . . . . . . . . .  6
   3.4     The <trigger> Element  . . . . . . . . . . . . . . . . . .  7
   3.4.1   The <changed> Element  . . . . . . . . . . . . . . . . . .  7
   3.4.1.1 The "changed-from" Attribute . . . . . . . . . . . . . . .  7
   3.4.1.2 The "changed-to" Attribute . . . . . . . . . . . . . . . .  7
   3.4.1.3 The "changed-by" Attribute . . . . . . . . . . . . . . . .  8
   3.4.1.4 Combination of Attributes  . . . . . . . . . . . . . . . .  8
   3.4.2   The <added> Element  . . . . . . . . . . . . . . . . . . .  8
   3.4.3   The <removed> Element  . . . . . . . . . . . . . . . . . .  8
   4.      Syntax for Referencing XML Items and Making Logical
           Expressions  . . . . . . . . . . . . . . . . . . . . . . .  8
   5.      IANA Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.      Examples . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6.1     Filter Criteria Using <what> Element . . . . . . . . . . .  9
   6.2     Filter Criteria Using <trigger> Element  . . . . . . . . . 10
   6.3     Filter Criteria Using <what> and <trigger> Elements  . . . 10
   6.4     Content Filter Using Namespaces  . . . . . . . . . . . . . 11
   6.5     Content Filter Using Only <Include> Elements . . . . . . . 11
   6.6     Two Content Filters as Filter Criteria . . . . . . . . . . 12
   7.      XML Schema for Filter Criteria . . . . . . . . . . . . . . 12
   8.      Security Requirements  . . . . . . . . . . . . . . . . . . 14
   9.      Acknowledgements . . . . . . . . . . . . . . . . . . . . . 15
           References . . . . . . . . . . . . . . . . . . . . . . . . 15
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 16
           Intellectual Property and Copyright Statements . . . . . . 18














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1. Conventions

   In this document, the key words 'MUST', 'MUST NOT', 'REQUIRED',
   'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY',
   and 'OPTIONAL' are to be interpreted as described in RFC 2119 [1]
   and indicate requirement levels for compliant implementations.

2. Introduction

   Filtering is a mechanism for defining the preferred content to be
   delivered and for specifying the rules for when the content should be
   delivered. See requirements in [9] and [10].

   The filtering mechanism is expected to be particularly valuable to
   users of mobile wireless access devices. The characteristics of the
   devices typically include high latency, low bandwidth, low data
   processing capabilities, small display, and limited battery power.
   Such devices can benefit from the ability to filter the amount of
   information generated at the source of the event notification.

   The SIP event notification framework [6] describes the usage of the
   Session Initiation Protocol (SIP) for subscriptions and notifications
   of changes to a state of a resource. The document does not describe a
   mechanism of how filtering of event notification information can be
   achieved.

   The structure of the filter criteria is described using the XML
   Schema. The filter criteria is presented as an XML document. The XML
   document contains the user's preference when notifications are to be
   sent to it and what they are to contain. The scope of the "when" part
   is triggering.

   The triggering is defined as enabling a subscriber to specify
   triggering rules for notifications where the criteria are based on
   changes of the package specific state information, e.g., for the
   presence information document [5] the change in the value of the
   <status> element.

   The functionality of the filtering regarding the SIP event
   notifications is specified in [11].

3. Structure of XML-Encoded Filter Criteria

   The filter criteria is an XML document [16] that MUST be well-formed
   and MUST be valid. The filter criteria XML documents MUST have the
   XML declaration and it SHOULD contain an encoding declaration in the
   XML declaration, for example; "<?XML version='1.0'
   encoding='UTF-8'?>". This specification makes use of XML namespaces



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   for identifying the XML schema of the filter criteria instance
   documents and document fragments.

   The namespace identifier for elements defined by this specification
   is a URN [13], using the namespace identifier 'ietf' defined by [14]
   and extended by [12]. This urn is:
   urn:ietf:params:xml:ns:simple-filter+xml.

   This namespace declaration indicates the namespace on which the
   filter criteria are based on.

3.1 The <filter-set> Root Element

   The root element of the filter criteria is <filter-set>.

   The <filter-set> element MUST contain the namespace definition
   mentioned above. With the optional "package" attribute it is possible
   to define the package to which the filter criteria is applied. This
   might be especially useful in cases where the XML document containing
   the filter criteria is separated from the events that makes use of it
   or from the protocol that usually carries it.

   The <filter-set> element MUST contain one or more <filter> elements.

3.2 The <filter> Element

   The <filter> element is used to specify the content of an individual
   filter.

   The <filter> MUST have an 'id' attribute. The value of the 'id'
   attribute MUST be unique within the <filter-set> element. The
   <filter> MAY have an 'uri' attribute. The value of the 'uri'
   attribute is the URI of the resource which information is requested
   for.

   The URI of the resource is useful in cases where the 'event list'
   extension [7] is used with a package. Since a subscription to an
   event package may be addressed to an event list, the "uri" attribute
   allows the subscriber to define a filter specific to an individual
   resource within that list. That resource may be another list. The
   'uri' attribute may, of course, carry the URI of the list itself. If
   the <filter> does not contain the 'uri' attribute, the filter applies
   to the resource indentified in the subscription request.

   The URI attribute MAY also carry a domain. In this case, the filter
   applies to resources in that domain. This can be used when a
   subscription is for a resource that is an event list with many
   resources from differing domains.



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   The <filter> MAY have a 'remove' attribute which indicates together
   with the 'id' attribute the existing filter to be removed. The value
   of the 'remove' attribute is of the type "Boolean". The default value
   is 'false'.

   The <filter> element MAY contain a <what> element and MAY contain one
   or more <trigger> elements, but MUST contain either the <what>
   element or the <trigger> element.

3.3 The <what> Element

   The <what> element is used to specify the content to be delivered to
   the user. It does not specify the exact content but the rules that
   are used to construct that information.

   The <what> element MAY contain one or more <include> elements and one
   or more <exclude> elements. However, the <what> element MUST contain
   at least one <include> element.  When more than one <include> element
   has been defined, the result is the union of all the <inlcude>
   elements. When more than one <exclude> element has been defined, the
   result is the union of all the <exclude> elements.

3.3.1 The <include> Element

   The <include> element is used to select the content to be delivered.
   Its value can identify XML elements, an attribute or a namespace of
   XML document to be filtered. This is indicated using the "type"
   attribute. The <include> element, if identifying elements, MUST
   identify one element only, unless the conditional expression results
   in more than one element with the same name being identified.

   Note that the resulting XML document MUST be valid. Therefore, in
   addition to including the elements identified with the <include>
   element, all other mandatory XML elements and/or attributes must be
   incorporated in the resulting XML document in order to make it valid.
   This, in practice, means that a subscriber defining a filter only
   needs to <include> optional elements and/or attributes, but may
   <include> mandatory elements and/or attributes as well.

   The following example selects the <status> element defined in the
   PIDF XML document [2]. This results in the selection of all the
   ancenstors of <status>. I.e. <basic> and <tuple>.

   <include type="xml-element">//tuple/status</include>.

   When identifying XML elements, the value may consist of two parts
   (similar to XPath [17]): the XML element selector and the condition
   (comparison and logical expressions). The syntax is defined in
   section Section 4 (see the definition of "selection".)




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3.3.1.1 The "type" Attribute

   The "type" attribute is used to describe the value of the <include>
   element. The following values are pre-defined: 'xml-element' and
   'namespace'. The "type" attribute is optional, and, if omitted, the
   default value is 'xml-element'.

   The syntax is defined in a way that follows XPath. The XML element
   selector appears first followed by the condition part in square
   brackets. In the XML element selector part the XML elements may be
   referenced by giving the full hierarchical path as: "/presence/tuple/
   status/basic", or by denoting the selection to cover any hierarchical
   level by its name as: "//basic" or using the wildcard "*" denoting
   any value in a certain level as "/*/watcher".

   Example references are listed as follows:


   o  Selection by using an XML element as a condition:

      *  //*[status/basic="open"]

      *  /presence/tuple[*/basic="open"]

   o  Selection by using XML attributes as a condition :

      *  //watcher[@duration-subscribed<500]

      *  /*/watcher[@event="rejected"]

   o  Selection by using two XML elements as a condition :

      *  //tuple[status/basic="open" and type="device"]


   The "namespace" value is used when the <include> element contains a
   value of a namespace. The value is the URI of the namespace. The
   resulting XML document is comprised of the elements defined within
   the namespace.

3.3.2 The <exclude> Element

   The <exclude> element is used to define exceptions to the set of XML
   elements and/or attributes selected by the <include> elements. Thus,
   those XML elements (including their lower level "child" elements)
   and/or attributes defined by the <exclude> element are not delivered.
   This is most useful when an <include> element identifies a namespace.




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   The <exclude> element has the optional "type" attribute (see the
   definition of the "type" in Section 3.3.1.1).

   The <exclude> element MUST NOT be used if there are no <include>
   element(s) in the same content filter.

3.4 The <trigger> Element

   The <trigger> element is used to identify the package specific
   changes that a resource has to encounter before the content is
   delivered to the subscriber. It can appear more than once in a filter
   document. Multiple appearances of this element denotes the "OR"
   operation. This means that updates to a resource that satisfy any of
   the <trigger> elements criteria constitute the content to be
   delivered.

   The <trigger> element MAY contain the <changed> element, the <added>
   element or the <removed>, but MUST contain at least one of the three
   elements. Any combination of the 3 elements is possible. Multiple
   appearances of those element within a <trigger> element denotes the
   "AND" operation. This means that updates to a resource that satisfy
   ALL of the <changed>, <added> and <removed> elements' criteria within
   the <trigger> element constitute the content to be delivered.

3.4.1 The <changed> Element

   The <changed> element is used to identify the XML element or
   attribute, from the package specific XML document, that must change,
   compared to the previous XML document, in order to activate the
   trigger and cause the content to be delivered. The XML element or
   attribute is identified using the syntax defined in Section 4 for the
   "reference". The <changed> element MUST identify only one XML element
   or attribute.

   The <changed> element MAY contain the "changed-from" attribute,
   "changed-to" attribute, "changed-by" attribute, or any combination of
   the three.

3.4.1.1 The "changed-from" Attribute

   A trigger is active when the XML element or attribute identified with
   the <changed> element has changed from the value indicated by this
   attribute to a different value.

3.4.1.2 The "changed-to" Attribute

   A trigger is active when the XML element or attribute identified with
   the <changed> element has changed to the value indicated by this



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   attribute from a different value.

3.4.1.3 The "changed-by" Attribute

   A trigger is active when the XML element or attribute identified with
   the <changed> element has changed by the value indicated by this
   attribute from a different value.

3.4.1.4 Combination of Attributes

   Any combination of the "changed-from", "changed-to", and "changed-by"
   attributes in the <changed> element is possible. For example, if the
   "changed-from" attribute was combined with the "changed-to" attribute
   it is interpreted as: the trigger is active when the XML element or
   attribute identified with the <changed> element has changed from the
   "changed-from" value to the "changed-to" value. Note that if the
   "changed-by" attribute is used in combination with the other
   attributes, the other attribute types MUST match the "changed-by"
   type of decimal.

3.4.2 The <added> Element

   The <added> element is used to trigger the content delivery when the
   XML element or attribute, identified in it, has been added to the new
   XML document in comparison to the previous XML document. It can be
   used, for example,  to learn of new services and/or capabilities
   subscribed to by the user, or services and/or capabilities that the
   user has now allowed the subscriber to see. The XML element or
   attribute is indicated using the syntax defined in Section 4 for the
   "reference".

   Note that if a filter includes both the content filter (<what>) part
   and the <added> element then the definitions of the <what> part
   SHOULD cover also the added elements, or otherwise the content is
   delivered without the items defined in the <added> element.

3.4.3 The <removed> Element

   The <removed> element is used to trigger the content to be delivered
   when the XML element or attribute, identified in it, has been removed
   from the new XML document in comparison to the previous XML document.
   The XML element or attribute is indicated using the syntax defined in
   Section 4 for the "reference".

4. Syntax for Referencing XML Items and Making Logical Expressions

   The ABNF [18] is used to describe the syntax for the expressions. The
   syntax is defined to be XPATH [17] compatible, but has only a



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   restricted set of capabilities of the XPATH. More information about
   the meaning of the items of the syntax can be found in [17]. The
   "abbreviated syntax" of the "node test" is used in the references
   ("reference"). The expression in the syntax relates to the predicate,
   comparision and logical expressions of the XPATH.

   selection = reference [expression]
   expression = "[" (elem-expr / attr-expr) 1*[oper (elem-expr / attr-expr)] "]"
   elem-expr = (elem-path / ".") compar value
   elem-path = (element / "*") 1*["/" / "*" / element] ["*" / element]
   attr-expr = [elem-path "/"] attribute compar value

   reference = elem-reference / attr-reference
   elem-reference =  "/" 1*("/" / "/*" / ("/" element))
   attr-reference = reference attribute

   oper = "and" / "or"
   compar = "=" / "<" / ">"
   element = [ns] string
   attribute = "@" [ns] string
   ns = string ":"
   string = <any sequence of data supported by XML in names of XML element, and/or attribute or prefixes of namespaces>
   value = <any sequence of data supported by XML as a value of the XML element and/or attribute>


5. IANA Considerations

   A new content type "application/simple-filter+xml" is defined to
   represent an XML MIME for the filter criteria.

   This specification follows the guidelines of RFC3023 [15]

   OPEN ISSUE: IANA registration template must be added later.

6. Examples

   The XML Schema for the XML document examples is specified in the
   Section 7.

6.1 Filter Criteria Using <what> Element

   A user wishes to get to know his friend's availability and
   willingness for messaging (SMS, IM and MMS) in order to know whether
   the friend is able to receive a message, the address to contact and
   the type of the message to be used.

   This example shows how to define a content filter. The whole content
   and upper level elements of the tuples of the presence information



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   are selected based on a condition defined by a logical expression.
   The condition is: select <class> elements that have a value "MMS",
   "SMS" or "IM".

   The <class> element is defined in [3] as an extension to PIDF [2].
   The first filter definition includes optional elements while the
   second filter definition shows only the minimum set of definitions.

   The first filter definition:

   <?xml version="1.0" encoding="UTF-8"?>
   <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter"
                xmlns:rpid="urn:ietf:params:xml:ns:pidf:rpid-tuple"
                xmlns:pidf="urn:ietf:params:xml:ns:pidf"
                package="presence">
         <filter id="mess" uri="sip:presentity@domain.com">
              <what>
                        <include type="xml-element">//pidf:tuple/pidf:status/pidf:basic[rpid:class="IM" or rpid:class="SMS" or rpid:class="MMS"]</include>
               </what>
           </filter>
   </filter-set>


6.2 Filter Criteria Using <trigger> Element

   A user requires to get informed when his colleaque becomes available
   by some communication mean(s). The user gets the full presence state
   of the colleaque.

   The filter selects the content to be delivered to the subscriber when
   a certain PIDF [2] tuple changes its <basic> status from 'CLOSED' to
   'OPEN'.

   <?xml version="1.0" encoding="UTF-8"?>
   <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter"
                xmlns:pidf="urn:ietf:params:xml:ns:pidf">
        <filter id="open_mean" uri="sip:presentity@domain.com">
           <trigger>
                    <changed changed-from="CLOSED" changed-to="OPEN">/pidf:presence/pidf:tuple/pidf:status/pidf:basic</changed>
           </trigger>
        </filter>
   </filter-set>


6.3 Filter Criteria Using <what> and <trigger> Elements

   A user wishes to get information about pending and waiting
   subscriptions in order to be able to authorise watchers to see his



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   presence information.

   The filter selects watcher information notifications [8] to be sent
   when a subscription status has changed to "pending" or "waiting". In
   the notification, only the watchers that have a status of "pending"
   or "waiting" are included.

   <?xml version="1.0" encoding="UTF-8"?>
   <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter"
                       package="winfo">
         <filter id="filterX" uri="sip:presentity@domain.com">
            <what>
                <include>wi:watcher[@wi:status="pending" or @wi:status="waiting"]</include>
            </what>
            <trigger>
                 <changed changed-to="pending">//wi:watcher/@wi:status@status</changed>
                 <changed changed-to="waiting">//wi:watcher/@wi:status@status</changed>
            </trigger>
         </filter>
   </filter-set>


6.4 Content Filter Using Namespaces

   A user turns her teminal on and the terminal automatically fetches
   general presence status and information about communication means
   from a certain pre-defined set of her buddies.

   The filter is defined to select XML elements belonging to the pidf
   namespace.

   <?xml version="1.0" encoding="UTF-8"?>
        <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter"
                          package="presence">
           <filter id="filter-PIDF" uri="sip:buddylist@domain.com">
                <what>
                        <include type="namespace"> urn:ietf:params:xml:ns:pidf
                        </include>
                </what>
               </filter>
        </filter-set>


6.5 Content Filter Using Only <Include> Elements

   A user wants to know if a group of his friends are available for
   gaming. He orders notifications about the current status and future
   changes of the game specific presence information.



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   This filter is defined to select the game specific tuple to be
   delivered.

   <?xml version="1.0" encoding="UTF-8"?>
        <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter"
                                xmlns:game-ext="urn:xml:ns:game-x"
                xmlns:pidf="urn:ietf:params:xml:ns:pidf"
                                package="presence">
           <filter id="filter-abc">
                <what>
                   <include>//pidf:tuple/pidf:status[game-ext:label="game-X"]</include>
                </what>
           </filter>
        </filter-set>


6.6 Two Content Filters as Filter Criteria

   The user is interested in getting up-to-date information about the
   communication means and contact addresses of his friends. The user
   wants to get also more information (e.g. location) about one of the
   friends in the list named Bob.  The PIDF element <note> is filtered
   out, i.e. excluded. The list was predefined as buddies@domain.com.

   <?xml version="1.0" encoding="UTF-8"?>
      <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter"
        xmlns:rpid="urn:ietf:params:xml:ns:pidf:rpid-tuple"
        xmlns:cip="urn:ietf:params:xml:ns:pidf:cipid"
        xmlns:pidf="urn:ietf:params:xml:ns:pidf">

            <filter id="8439" uri="sip:buddies@domain.com">
                <what>
                        <include>//pidf:tuple/pidf:status/pidf:basic[rpid:type="service"]</include>
                </what>
            </filter>

            <filter id="999" uri="sip:bob@domain.com">
               <what>
                        <include type="namespace">urn:ietf:params:xml:ns:pidf</exclude>
                        <exclude>//pidf:tuple/pidf:note</exclude>
                </what>
            </filter>
      </filter-set>


7. XML Schema for Filter Criteria

   XML Schema Implementation (Normative)

   <?xml version="1.0" encoding="UTF-8"?>



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   <xs:schema targetNamespace="urn:ietf:params:xml:ns:simple-filter"
        xmlns="urn:ietf:params:xml:ns:simple-filter"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">

        <xs:import namespace="http://www.w3.org/XML/1998/namespace"
                         schemaLocation="http://www.w3.org/2001/xml.xsd"/>

        <xs:annotation>
          <xs:documentation xml:lang="en">
            XML Schema Definition for Filter Criteria.
          </xs:documentation>
        </xs:annotation>

        <xs:element name="filter-set" type="FilterSetType"/>

        <xs:complexType name="FilterSetType">
          <xs:sequence>
            <xs:element name="filter" type="FilterType"
                         minOccurs="1"    maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="package" type="xs:string" use="optional"/>
        </xs:complexType>

        <xs:complexType name="FilterType">
           <xs:sequence>
               <xs:element name="what" type="WhatType" minOccurs="0" maxOccurs="1"/>
               <xs:element name="trigger" type="TriggerType" minOccurs="0" maxOccurs="unbounded"/>
           </xs:sequence>
           <xs:attribute name="id"  type="xs:string" use="required"/>
           <xs:attribute name="uri" type="xs:anyURI" use="optional"/>
           <xs:attribute name="remove" type="xs:boolean" default="false" use="optional"/>
           <xs:anyAttribute namespace="##other" processContents="lax"/>
        </xs:complexType>

      <xs:complexType name="WhatType">
         <xs:sequence>
             <xs:element name="include" type="InclType" minOccurs="1" maxOccurs="unbounded"/>
             <xs:element name="exclude" type="ExclType" minOccurs="0" maxOccurs="unbounded"/>
         </xs:sequence>
      </xs:complexType>

      <xs:complexType name="InclType">
         <xs:simpleContent>
          <xs:extension base="xs:string">
                <xs:attribute name="type" type="TypeType" default="xml-element" use="optional"/>
               <xs:anyAttribute namespace="##other" processContents="lax"/>
          </xs:extension>
         </xs:simpleContent>



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      </xs:complexType>

      <xs:complexType name="ExclType">
         <xs:simpleContent>
          <xs:extension base="xs:string">
                <xs:attribute name="type" type="TypeType" default="xml-element" use="optional"/>
               <xs:anyAttribute namespace="##other" processContents="lax"/>
          </xs:extension>
         </xs:simpleContent>
      </xs:complexType>

      <xs:simpleType name="TypeType">
         <xs:restriction base="xs:string">
                <xs:enumeration value="xml-element"/>
                <xs:enumeration value="namespace"/>
                <xs:enumeration value="token"/>
         </xs:restriction>
      </xs:simpleType>


        <xs:complexType name="TriggerType">
           <xs:sequence>
               <xs:element name="changed" type="ChangedType" minOccurs="0" maxOccurs="unbounded"/>
               <xs:element name="added" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>
               <xs:element name="removed" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>
                <xs:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
           </xs:sequence>
        </xs:complexType>

         <xs:complexType name="ChangedType">
            <xs:simpleContent>
                <xs:extension base="xs:string">
                   <xs:attribute name="changed-from" type="xs:anySimpleType" use="optional"/>
                   <xs:attribute name="changed-to" type="xs:anySimpleType" use="optional"/>
                   <xs:attribute name="changed-by" type="xs:decimal" use="optional"/>
                   <xs:anyAttribute namespace="##other" processContents="lax"/>
                </xs:extension>
            </xs:simpleContent>
         </xs:complexType>

   </xs:schema>


8. Security Requirements

   The filters in the body in a SIP message has a significant effect on
   the ways in which the request is handled at a server. As a result, it
   is especially important that messages containing this extension be



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   authenticated and authorised.

   Processing of requests and looking up filter criteria requires a set
   of operations and searches, which can require some amount of
   computation. This enables a DoS attack whereby a user can send
   requests with substantial number of messages with large contents, in
   the hopes of overloading the server. To counter this, the server
   SHOULD only allow filters with no more than about 20 occurances of
   the <what>, <changed>, <added> and <removed> elements.

   Requests can reveal sensitive information about a UA's capabilities.
   If this information is sensitive, it SHOULD be encrypted using SIP S/
   MIME capabilities.

   All filtering related security measures discussed in [6] MUST be
   followed along with package specific security.

9. Acknowledgements

   The authors would like to thank Jonathan Rosenberg, Henning
   Schulzrinne, Tim Moran, Jari Urpalainen, Sreenivas Addagatla and all
   the active SIMPLE mailing list contributors for their valuable input.

References

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

   [2]   Sugano, H., "CPIM Presence Information Data Format",
         draft-ietf-impp-cpim-pidf-08.txt (work in progress), May 2003.

   [3]   Schulzrinne, H., "RPID -- Rich Presence Information Data
         Format",  draft-ietf-simple-rpid-00.txt (work in progress),
         July 2003.

   [4]   Schulzrinne, H., "CIPID: Contact Information in Presence
         Information Data Format",  draft-ietf-simple-cipid-00.txt (work
         in progress), August 2003.

   [5]   Rosenberg, J., "Session Initiation Protocol (SIP) Extensions
         for Presence",  draft-ietf-simple-presence-10.txt, January
         2003.

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

   [7]   Roach, A., "A Session Initiation Protocol (SIP) Event
         Notification Extension for Resource Lists",



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         draft-ietf-simple-event-list-04.txt, June 2003.

   [8]   Rosenberg, J., "An Extensible Markup Language (XML) Based
         Format for Watcher Information",
         draft-ietf-simple-winfo-format-04.txt, January 2003.

   [9]   Khartabil, H., "Requirements for Presence Specific Event
         Notification Filtering",
         draft-ietf-simple-pres-filter-reqs-03.txt (work in progress),
         January 2004.

   [10]  Kiss, K., "Requirements for Filtering of Watcher Information",
         draft-ietf-simple-winfo-filter-reqs-01.txt (work in progress),
         January 2004.

   [11]  Khartabil, H., "Functional Description of Event Notification
         Filtering",  draft-simple-filter-funct-00.txt (work in
         progress), February 2004.

   [12]  Mealling, M., "The IETF XML Registry",
         draft-mealling-iana-xmlns-registry-04.txt, June 2002.

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

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

   [15]  Murata, M., "XML Media Types", RFC 3023, March 1997.

   [16]  Bray, T., "Exensible Markup Language (XML) 1.0 (Second
         Edition)",  W3C CR CR-xml11-20011006, October 2000.

   [17]  Clark, J., "XML Path Language (XPath) Version 1.0",  W3C REC
         REC-xpath-19991116, November 1999.

   [18]  Crocker, D., "Augmented BNF for Syntax Specifications: ABNF",
         RFC 2234, November 1997.














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Authors' Addresses

   Hisham Khartabil
   Nokia
   P.O. Box 321
   Helsinki
   Finland

   Phone: +358 7180 76161
   EMail: hisham.khartabil@nokia.com


   Eva Leppanen
   Nokia
   P.O BOX 785
   Tampere
   Finland

   Phone: +358 7180 77066
   EMail: eva-maria.leppanen@nokia.com


   Mikko Lonnfors
   Nokia
   Itamerenkatu 00180
   Helsinki
   Finland

   Phone: + 358 50 4836402
   EMail: mikko.lonnfors@nokia.com


   Jose Costa-Requena
   Nokia
   P.O. Box 321
   FIN-00045 NOKIA GROUP
   FINLAND

   Phone: +358 71800 8000
   EMail: jose.costa-requena@nokia.com











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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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