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rfc:rfc4661

Network Working Group H. Khartabil Request for Comments: 4661 Telio Category: Standards Track E. Leppanen

                                                           M. Lonnfors
                                                      J. Costa-Requena
                                                                 Nokia
                                                        September 2006
        An Extensible Markup Language (XML)-Based Format for
                    Event Notification Filtering

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

 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 whereby filtering of event notification information can
 be achieved.  Filtering is a mechanism for defining the preferred
 notification information to be delivered and for specifying triggers
 that cause that information to be delivered.  In order to enable
 this, a format is needed to enable the subscriber to describe the
 state changes of a resource that cause notifications to be sent to it
 and what those notifications are to contain.  This document presents
 a format in the form of an XML document.

Khartabil, et al. Standards Track [Page 1] RFC 4661 XML Based Format for Filtering September 2006

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
 2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
 3.  Structure of XML-Encoded Simple-Filter . . . . . . . . . . . .  4
     3.1.  MIME Type for Simple-Filter Document . . . . . . . . . .  4
     3.2.  The <filter-set> Root Element  . . . . . . . . . . . . .  4
     3.3.  The <ns-bindings> Element  . . . . . . . . . . . . . . .  4
     3.4.  The <filter> Element . . . . . . . . . . . . . . . . . .  5
     3.5.  The <what> Element . . . . . . . . . . . . . . . . . . .  6
           3.5.1.  The <include> Element  . . . . . . . . . . . . .  6
           3.5.2.  The <exclude> Element  . . . . . . . . . . . . .  7
           3.5.3.  The 'type' Attribute . . . . . . . . . . . . . .  7
     3.6.  The <trigger> Element  . . . . . . . . . . . . . . . . .  8
           3.6.1.  The <changed> Element  . . . . . . . . . . . . .  8
           3.6.2.  The <added> Element  . . . . . . . . . . . . . .  9
           3.6.3.  The <removed> Element  . . . . . . . . . . . . . 10
 4.  XML Schema Extensibility . . . . . . . . . . . . . . . . . . . 10
 5.  Syntax for Referencing XML Items and Making Logical
     Expressions  . . . . . . . . . . . . . . . . . . . . . . . . . 10
 6.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  Filter Criteria Using <what> Element . . . . . . . . . . 12
     6.2.  Filter Criteria Using <trigger> Element  . . . . . . . . 13
     6.3.  Filter Criteria Using <what> and <trigger> Elements  . . 13
     6.4.  Content Filter Using Namespaces  . . . . . . . . . . . . 14
     6.5.  Content Filter Using Only <include> Elements . . . . . . 14
     6.6.  Two Content Filters as Filter Criteria . . . . . . . . . 15
 7.  XML Schema for Filter Criteria . . . . . . . . . . . . . . . . 16
 8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
 9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
     9.1.  application/simple-filter+xml MIME TYPE  . . . . . . . . 19
     9.2.  URN Sub-Namespace Registration for
         urn:ietf:params:xml:ns:simple-filter . . . . . . . . . . . 20
     9.3.  Schema Registration  . . . . . . . . . . . . . . . . . . 20
 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     11.1. Normative References . . . . . . . . . . . . . . . . . . 20
     11.2. Informative References . . . . . . . . . . . . . . . . . 21

Khartabil, et al. Standards Track [Page 2] RFC 4661 XML Based Format for Filtering September 2006

1. Introduction

 The SIP event notification framework [2] 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 whereby filtering of event notification information can
 be achieved.
 Filtering is a mechanism for defining the preferred notification
 information, referred to as content, to be delivered and for
 specifying the rules for when that information should be delivered.
 The filtering mechanism is expected to be particularly valuable and
 primarily applicable 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.  However, implementers need to be aware of the
 computational burden on the source of the event notification.  This
 is discussed further in Section 8.
 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 as to 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 event package [2] specific state information, e.g.,
 for the presence information document [15], the change in the value
 of the <status> element.
 The functionality of the filtering regarding the SIP event
 notifications is specified in [3].

2. 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.
 Throughout the document, the "resulting XML document" refers to the
 final XML document that carries state information to be delivered to
 the subscriber after the filters have been applied to it.

Khartabil, et al. Standards Track [Page 3] RFC 4661 XML Based Format for Filtering September 2006

 "Content" refers to the XML document that appears in a notification
 reflecting the state of a resource.

3. Structure of XML-Encoded Simple-Filter

 A simple-filter is an XML document [8] that MUST be well formed and
 MUST be valid according to schemas, including extension schemas,
 available to the validater, and applicable to the XML document.  The
 simple-filter documents MUST be based on XML 1.0 and MUST be encoded
 using UTF-8.
 The namespace identifier for elements defined by this specification
 is a URN [5], which uses the namespace identifier 'ietf' defined by
 [6] and extended by [4].  This urn is:
 urn:ietf:params:xml:ns:simple-filter.
 This namespace declaration indicates the namespace on which the
 filter criteria are based.

3.1. MIME Type for Simple-Filter Document

 The MIME type for the simple-filter document is "application/
 simple-filter+xml".  Any transport protocol (SIP [12], for example)
 used to carry the filters that also carries payload type information
 MUST identify the payload as MIME type
 "application/simple-filter+xml" (for example, a Content-Type header
 field).

3.2. The <filter-set> Root Element

 The root element of the filter criteria is <filter-set>.
 The <filter-set> element contains 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 make use of it
 or from the protocol that usually carries it.
 The <filter-set> element may contain one <ns-bindings> element.
 The <filter-set> element contains one or more <filter> elements.

3.3. The <ns-bindings> Element

 The <ns-bindings> element is used to bind namespaces to local
 prefixes used in expressions that select elements or attributes using

Khartabil, et al. Standards Track [Page 4] RFC 4661 XML Based Format for Filtering September 2006

 the syntax in Section 5.  Those prefixes apply to the <include>,
 <exclude>, <changed>, <added>, and <removed> elements.
 The <ns-bindings> element contains one or more <ns-binding> elements.
 Each <ns-binding> element has a 'prefix' attribute.  The value of the
 'prefix' attribute is a prefix used to qualify the elements pointed
 to by the expression.  The <ns-binding> element also has a 'urn'
 attribute that identifies the namespace that the prefix represents.

3.4. The <filter> Element

 The <filter> element is used to specify the content of an individual
 filter.
 The <filter> element has an 'id' attribute.  The value of the 'id'
 attribute MUST be unique within the <filter-set> element.  The
 <filter> MAY have a 'uri' attribute.  The value of the 'uri'
 attribute is the URI of the resource to which the filter applies.
 The <filter> MAY have a 'domain' attribute.  The value of the
 'domain' attribute is the domain of the resources to which the filter
 applies.  The 'uri' attribute and the 'domain' attribute MUST NOT
 appear together in the <filter>.
 The URI of the resource is useful in cases where the 'event list'
 extension [17] 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 identified in the subscription request.
 The 'domain' attribute carries a domain.  In this case, the filter
 applies to resources whose URI has a domain part matching that
 domain.  This can be used when a subscription is for a resource that
 is an event list with many resources from differing domains.
 URI matching is done according to the matching rules defined for a
 particular scheme.  When matching domains, the user part of the URI
 is ignored for matching purposes.
 The <filter> MAY have a 'remove' attribute that together with the
 'id' attribute indicates the existing filter to be removed.  The
 value of the 'remove' attribute is of the type "Boolean".  The
 default value is "false".

Khartabil, et al. Standards Track [Page 5] RFC 4661 XML Based Format for Filtering September 2006

 The <filter> MAY have an 'enabled' attribute that indicates whether a
 filter is enabled or disabled.  The value of the 'enabled' attribute
 is of the type "Boolean".  The default value is "true".
 The <filter> element MAY contain a <what> element and MAY contain one
 or more <trigger> elements, but it MUST contain either the <what>
 element or the <trigger> element when the filter is being enabled for
 the first time.  When a filter is disabled by setting the 'enabled'
 attribute to "false", the <what> and <trigger> elements MAY be
 omitted.  Similarly, when a filter is re-enabled by setting the
 'enabled' attribute to "true", the <what> and <trigger> elements MAY
 be omitted.
 Filter contents can be changed by changing the contents in the <what>
 and <trigger> elements and maintaining the value of the filter 'id'
 attribute.

3.5. 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.  When more than one <include> element has
 been defined, the results are additive.  That is, each <include>
 element adds an element or attribute to the resulting XML document.
 When more than one <exclude> element has been defined, each <exclude>
 element value depletes the contents of the resulting XML document.

3.5.1. The <include> Element

 The <include> element is used to select the content to be delivered.
 Its value can identify an XML element, an attribute, or a namespace
 of an XML document to be filtered.  This is indicated using the
 'type' attribute.
 Note that the resulting XML document MUST be valid.  Therefore, in
 addition to including the elements identified with the <include>
 element value, 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.
 There are also cases where a filter selects an attribute that belongs
 to an optional element.  In this case, the optional element needs to
 appear in the resulting XML document.

Khartabil, et al. Standards Track [Page 6] RFC 4661 XML Based Format for Filtering September 2006

 The syntax defined in Section 5 (see the definition of "selection")
 MUST be used.  The following example selects the <basic> element
 defined in the PIDF [13].  This results in the selection of the
 <basic> element as well as all the ancestors, i.e., <status> and
 <tuple>.
 <include type="xpath">/presence/tuple/status/basic</include>.

3.5.2. 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,
 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.
 The <exclude> element has the optional 'type' attribute (see the
 definition of the 'type' in Section 3.5.3).
 Note that the resulting XML document MUST be valid.  Therefore, if
 the step in applying the <exclude> element value to an XML document
 results in an invalid document according to the schema, that step
 MUST be reversed, resulting in the elements and/or attributes being
 re-introduced into the resulting XML document with their previous
 values in order to make it valid.  This, in practice, means that a
 subscriber defining a filter only needs to <exclude> optional
 elements and/or attributes, but SHOULD NOT <exclude> mandatory
 elements and/or attributes.
 The syntax MUST follow Section 5.

3.5.3. The 'type' Attribute

 The 'type' attribute is used to describe the value of the <include>
 and <exclude> elements.  The following values are pre-defined:
 "xpath" and "namespace".  The 'type' attribute is optional, and, if
 omitted, the default value is "xpath".
 The "xpath" value is used when the <include> or <exclude> element
 contains a value following the syntax in Section 5 that selects an
 element or an attribute.
 The "namespace" value is used when the <include> or <exclude> 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.

Khartabil, et al. Standards Track [Page 7] RFC 4661 XML Based Format for Filtering September 2006

3.6. 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> element.  Multiple appearances of this element denote 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>, <added>, or
 <removed> elements, but it MUST contain at least one of the three
 elements.  Any combination of the 3 elements is possible.  Multiple
 appearances of those elements 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.

3.6.1. The <changed> Element

 The <changed> element is used to identify the XML element or
 attribute, from the package-specific XML document, whose value MUST
 change from that of the "previous XML document", in order to activate
 the trigger and cause the content to be delivered.  Previous XML
 document" in this context refers to the raw version of the most
 recent XML document that was sent to the subscriber, before the
 filters were applied to it.  The XML element or attribute MUST be
 expressed using the syntax defined in Section 5 for the "reference"
 ABNF.
 The <changed> element MAY contain the 'from' attribute, the 'to'
 attribute, the 'by' attribute, or any combination of the three.  The
 absence of all of those attributes means a change of any sort to the
 value of the element or attribute activates the trigger.  An update
 to the element or attribute value with an identical value is not a
 change.
 Comparison of a change is done according to the element or
 attribute's lexical rules.

3.6.1.1. The '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.

Khartabil, et al. Standards Track [Page 8] RFC 4661 XML Based Format for Filtering September 2006

3.6.1.2. The '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
 attribute from a different value.

3.6.1.3. The 'by' Attribute

 A trigger is active when the XML element or attribute identified with
 the <changed> element has changed by at least the amount indicated by
 this attribute from a different value.  That is, the 'by' attribute
 applies only to numerical values and indicates a delta with respect
 to the current value that an attribute or element (identified in the
 <changed> element) needs to change before it is selected.  For
 example, if the 'by' attribute is set to 2 and the current value of
 the element/attribute is 6, the element/attribute is selected when it
 reaches (or exceeds) the value 8 or when it decreases to 4 or a lower
 value.

3.6.1.4. Combination of Attributes

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

3.6.2. The <added> Element

 The <added> element triggers content delivery when the XML element it
 identifies has been added to the document being filtered (that is,
 this instance of that element appears in the current document, but
 not in the previous 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 MUST be expressed
 using the syntax defined in Section 5 for the "reference" ABNF.
 Note that if a filter includes both the content filter (<what>) part
 and the <added> element, then the definitions of the <what> part
 SHOULD also cover the added elements.  Otherwise, the content is
 delivered without the items defined in the <added> element.

Khartabil, et al. Standards Track [Page 9] RFC 4661 XML Based Format for Filtering September 2006

3.6.3. The <removed> Element

 The <removed> element triggers content delivery when the XML element
 it identifies has been removed from the document being filtered (that
 is, this instance of that element appeared in the previous document,
 but not in this document).  The XML element or attribute MUST be
 expressed using the syntax defined in Section 5 for the "reference"
 ABNF.

4. XML Schema Extensibility

 The simple-filter document is meant to be extended.  An extension
 takes place by defining a new set of elements in a new namespace,
 governed by a new schema.  Every extension MUST have an appropriate
 XML namespace assigned to it.  The XML namespace of the extension
 MUST be different from the namespaces defined in this specification.
 The extension MUST NOT change the syntax or semantics of the schemas
 defined in this document.  All XML tags and attributes that are part
 of the extension MUST be appropriately qualified so as to place them
 within that namespace and MUST be designed such that receivers can
 safely ignore such extensions.
 This specification defines explicit places where new elements or
 attributes from an extension can be placed.  These are explicitly
 indicated in the schemas by the <any> and <anyAttribute> elements.
 Extensions to this specification MUST specify where their elements
 can be placed within the document.
 As a result, a document that contains extensions will require
 multiple schemas in order to determine its validity - a schema
 defined in this document, along with those defined by extensions
 present in the document.  Because extensions occur by adding new
 elements and attributes governed by new schemas, the schemas defined
 in this document are fixed and would only be changed by a revision to
 this specification.  Such a revision, should it take place, would
 endeavor to allow documents compliant to the previous schema to
 remain compliant to the new one.  As a result, the schemas defined
 here don't provide explicit schema versions, as this is not expected
 to be needed.

5. Syntax for Referencing XML Items and Making Logical Expressions

 The ABNF [10] is used to describe the syntax for the expressions.
 The syntax is defined to be XPATH [9] compatible but has only a
 restricted set of capabilities of the XPATH.  More information about
 the meaning of the items of the syntax can be found in [9].  The
 "abbreviated syntax" of the "node test" is used in the references
 ("reference").  The expression in the syntax relates to the

Khartabil, et al. Standards Track [Page 10] RFC 4661 XML Based Format for Filtering September 2006

 predicate, comparison, and logical expressions of the XPATH.  If an
 XPATH expression evaluates to more than one element at a certain
 step, the filter applies to all the elements that are evaluated.
 That is, if a filter including an element evaluates to 2 elements,
 both elements are included as a result.
 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>
 When identifying XML elements or attributes, the value may consist of
 two parts: the XML element/attribute selector and the condition
 (comparison and logical expressions).  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",
 by denoting the selection to cover any hierarchical level by its name
 as: "//tuple/status/basic", or using the wildcard "*", denoting any
 value in a certain level as "/*/watcher".
 Example references are listed as follows:
 o  Selecting an element by using an XML element as a condition:
    *  //*[status/basic="open"]
    *  /presence/tuple[*/basic="open"]
 o  Selecting an element by using XML attributes as a condition:
    *  //watcher[@duration-subscribed<500]
    *  /*/watcher[@event="rejected"]

Khartabil, et al. Standards Track [Page 11] RFC 4661 XML Based Format for Filtering September 2006

 o  Selecting an element by using two XML elements as a condition:
    *  //tuple[status/basic="open" and type="device"]
 o  Selecting an attribute:
    *  //watcher/@duration-subscribed
 In some cases, due to the design of the XML schema, the XPATH-like
 expression results in identification of more than one element with
 the same name (the XPATH expression may not have uniquely identified
 an element at every step).  In those cases, all elements identified
 are selected.
 When evaluating XPATH location steps, namespace expansion follows
 XPATH 1.0 [9] semantics, i.e., if the QName does not have a prefix,
 then the namespace URI in the expanded name is null.  With
 non-default namespaces, expansion is done according to the given
 <ns-bindings> definitions.  When a default namespace is used in the
 document, the <ns-binding> element SHOULD be used to define an equal
 URI with some prefix in order to have a valid XPATH evaluation in
 location steps.

6. Examples

 The XML Schema for the XML document examples is specified in
 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 <basic>
 element as well as all parent elements are selected based on a
 condition defined by a logical expression.  The condition is <class>
 elements that have a value "MMS", "SMS", or "IM".
 The <class> element is defined in [14] as an extension to PIDF [13].
 <?xml version="1.0" encoding="UTF-8"?>
 <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter">
   <ns-bindings>
     <ns-binding prefix="pidf" urn="urn:ietf:params:xml:ns:pidf"/>
     <ns-binding prefix="rpid"
                        urn="urn:ietf:params:xml:ns:pidf:rpid"/>
   </ns-bindings>
   <filter id="123" uri="sip:presentity@example.com">

Khartabil, et al. Standards Track [Page 12] RFC 4661 XML Based Format for Filtering September 2006

     <what>
       <include type="xpath">
         /pidf:presence/pidf:tuple[rpid:class="IM" or rpid:class="SMS"
         or rpid:class="MMS"]/pidf:status/pidf:basic
       </include>
     </what>
   </filter>
 </filter-set>

6.2. Filter Criteria Using <trigger> Element

 A user requires to be informed when his colleague becomes available
 by some communication means.  The user gets the full presence state
 of the colleague when a certain PIDF [13] tuple <basic> status
 changes from "closed" to "open".
 <?xml version="1.0" encoding="UTF-8"?>
 <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter">
   <ns-bindings>
     <ns-binding prefix="pidf" urn="urn:ietf:params:xml:ns:pidf"/>
   </ns-bindings>
   <filter id="123" uri="sip:presentity@example.com">
     <trigger>
       <changed from="CLOSED" 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
 presence information.
 The filter selects watcher information notifications [16] 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">
   <ns-bindings>
     <ns-binding prefix="wi"
                        urn="urn:ietf:params:xml:ns:watcherinfo"/>
   </ns-bindings>
   <filter id="123" uri="sip:presentity@example.com">

Khartabil, et al. Standards Track [Page 13] RFC 4661 XML Based Format for Filtering September 2006

     <what>
       <include>
         /wi:watcherinfo/wi:watcher-list/wi:watcher[@status="pending"
         or @status="waiting"]
       </include>
     </what>
     <trigger>
       <changed to="pending">
         /wi:watcherinfo/wi:watcher-list/wi:watcher/@status
       </changed>
     </trigger>
     <trigger>
       <changed to="waiting">
         /wi:watcherinfo/wi:watcher-list/wi:watcher/@status
       </changed>
     </trigger>
   </filter>
 </filter-set>

6.4. Content Filter Using Namespaces

 A user turns her terminal 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">
   <filter id="123" uri="sip:buddylist@example.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 is available for
 gaming.  He orders notifications about the current status and future
 changes of the game-specific presence information.
 This filter is defined to select the game-specific tuple to be
 delivered.

Khartabil, et al. Standards Track [Page 14] RFC 4661 XML Based Format for Filtering September 2006

 <?xml version="1.0" encoding="UTF-8"?>
 <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter" >
   <ns-bindings>
     <ns-binding prefix="game-ext"
                        urn="urn:ietf:params:xml:ns:game-ext"/>
   </ns-bindings>
   <filter id="123">
     <what>
       <include>
         /pidf:presence/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
 also wants to get 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@example.com.
 <?xml version="1.0" encoding="UTF-8"?>
 <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter">
   <ns-bindings>
     <ns-binding prefix="pidf" urn="urn:ietf:params:xml:ns:pidf"/>
     <ns-binding prefix="rpid"
                        urn="urn:ietf:params:xml:ns:pidf:rpid"/>
   </ns-bindings>
   <filter id="8439" uri="sip:buddies@example.com">
     <what>
       <include>
         /pidf:presence/pidf:tuple[rpid:class="service"]/pidf:status/
         pidf:basic
       </include>
     </what>
     </filter>
   <filter id="999" uri="sip:bob@example.com">
     <what>
       <include type="namespace">
         urn:ietf:params:xml:ns:pidf
       </include>
       <exclude>
         /pidf:presence/pidf:tuple/pidf:note
       </exclude>
     </what>

Khartabil, et al. Standards Track [Page 15] RFC 4661 XML Based Format for Filtering September 2006

   </filter>
 </filter-set>

7. XML Schema for Filter Criteria

 XML Schema Implementation (Normative)
 <?xml version="1.0" encoding="UTF-8"?>
 <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"
        elementFormDefault="qualified">
   <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="ns-bindings" type="NSBindings"
                             minOccurs="0" maxOccurs="1"/>
         <xs:element name="filter" type="FilterType"
                             minOccurs="1"
       maxOccurs="unbounded"/>
         </xs:sequence>
       <xs:attribute name="package" type="xs:string" use="optional"/>
       <xs:anyAttribute namespace="##other" processContents="lax"/>
     </xs:complexType>
   <xs:complexType name="NSBindings">
     <xs:sequence>
       <xs:element name="ns-binding" type="NSBinding"
                           minOccurs="1" maxOccurs="unbounded"/>
     </xs:sequence>
   </xs:complexType>
   <xs:complexType name="NSBinding">
     <xs:attribute name="prefix" type="xs:string" use="required"/>
     <xs:attribute name="urn" type="xs:anyURI" use="required"/>
   </xs:complexType>

Khartabil, et al. Standards Track [Page 16] RFC 4661 XML Based Format for Filtering September 2006

   <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:any namespace="##other" processContents="lax"
                     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="domain" type="xs:string" use="optional"/>
     <xs:attribute name="remove" type="xs:boolean" use="optional"
                          default="false"/>
     <xs:attribute name="enabled" type="xs:boolean" use="optional"
                          default="true"/>
     <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:complexType>
   <xs:complexType name="WhatType">
     <xs:sequence>
       <xs:element name="include" type="InclType"
                           minOccurs="0" maxOccurs="unbounded"/>
       <xs:element name="exclude" type="ExclType"
                           minOccurs="0" maxOccurs="unbounded"/>
       <xs:any namespace="##other" processContents="lax"
                     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="xpath" use="optional"/>
         <xs:anyAttribute namespace="##other" processContents="lax"/>
       </xs:extension>
     </xs:simpleContent>
   </xs:complexType>
   <xs:complexType name="ExclType">
     <xs:simpleContent>
       <xs:extension base="xs:string">
         <xs:attribute name="type" type="TypeType"
                              default="xpath" use="optional"/>
         <xs:anyAttribute namespace="##other" processContents="lax"/>
       </xs:extension>
     </xs:simpleContent>

Khartabil, et al. Standards Track [Page 17] RFC 4661 XML Based Format for Filtering September 2006

 </xs:complexType>
   <xs:simpleType name="TypeType">
     <xs:restriction base="xs:string">
       <xs:enumeration value="xpath"/>
       <xs:enumeration value="namespace"/>
     </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="from" type="xs:anySimpleType"
                              use="optional"/>
         <xs:attribute name="to" type="xs:anySimpleType"
                              use="optional"/>
         <xs:attribute name="by" type="xs:decimal"
                              use="optional"/>
         <xs:anyAttribute namespace="##other" processContents="lax"/>
       </xs:extension>
     </xs:simpleContent>
   </xs:complexType>
 </xs:schema>

8. Security Considerations

 The filters in the body in a SIP message have 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
 authenticated and authorised.  Authentication can be achieved using
 the Digest Authentication mechanism described in [12].  The
 authorisation decision is based on the permissions that the resource
 (notifier) has given to the watcher.  An example of such an
 auhorisation policy can be found in [18].

Khartabil, et al. Standards Track [Page 18] RFC 4661 XML Based Format for Filtering September 2006

 Requests can reveal sensitive information about a UA's capabilities.
 If this information is sensitive, it SHOULD be encrypted using SIP
 S/MIME capabilities [11].
 All filtering-related security measures discussed in [2] MUST be
 followed along with package-specific security.

9. IANA Considerations

 This document registers a new MIME type, "application/
 simple-filter+xml", and registers a new XML namespace.
 This specification follows the guidelines of RFC3023 [7].

9.1. application/simple-filter+xml MIME TYPE

 MIME media type: application
 MIME subtype name: simple-filter+xml
 Mandatory parameters: none
 Optional parameters: Same as charset parameter application/xml, as
 specified in RFC 3023 [7].
 Encoding considerations: Same as encoding considerations of
 application/xml, as specified in RFC 3023 [7].
 Security considerations: See section 10 of RFC 3023 [7] and section
 Section 8 of this document.
 Interoperability considerations: none.
 Published specification: This document.
 Applications that use this media type: This document type has been
 used to support the SIP-based Event notification framework and its
 packages.
 Additional information:
 Magic number: None
 File extension: .cl or .xml
 Macintosh file type code: "TEXT"

Khartabil, et al. Standards Track [Page 19] RFC 4661 XML Based Format for Filtering September 2006

 Personal and email address for further information: Hisham Khartabil
 (hisham.khartabil@telio.no)
 Intended Usage: COMMON
 Author/change controller: The IETF

9.2. URN Sub-Namespace Registration for

    urn:ietf:params:xml:ns:simple-filter
 This section registers a new XML namespace, as per guidelines in the
 IETF XML Registry [4].
 URI: The URI for this namespace is
 urn:ietf:params:xml:ns:simple-filter.
 Registrant Contact: IETF, SIMPLE working group, Hisham Khartabil
 (hisham.khartabil@telio.no)

9.3. Schema Registration

 This section registers a new XML schema per the procedures in [4].
 URI: urn:ietf:params:xml:ns:simple-filter
 Registrant Contact: IETF, SIMPLE working group, Hisham Khartabil
 (hisham.khartabil@telio.no).
 The XML for this schema can be found as the sole content of
 Section 7.

10. Acknowledgements

 The authors would like to thank Jonathan Rosenberg, Henning
 Schulzrinne, Tim Moran, Jari Urpalainen, Sreenivas Addagatla,
 Miguel-Angel Garcia Martin, Mary Barnes, Paul Kyzivat, Robert Sparks,
 and Elwyn Davies for their valuable input and comments.

11. References

11.1. Normative References

 [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.
 [2]   Roach, A. B., "Session Initiation Protocol (SIP)-Specific Event
       Notification", RFC 3265, June 2002.

Khartabil, et al. Standards Track [Page 20] RFC 4661 XML Based Format for Filtering September 2006

 [3]   Khartabil, H., Leppanen, E., Lonnfors, M., and J. Costa-
       Requena, "Functional Description of Event Notification
       Filtering", RFC 4660, September 2006.
 [4]   Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
       January 2004.
 [5]   Moats, R., "URN Syntax", RFC 2141, May 1997.
 [6]   Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
       August 1999.
 [7]   Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
       RFC 3023, January 2001.
 [8]   Bray, T., "Exensible Markup Language (XML) 1.0 (Second
       Edition)",  W3C CR CR-xml11-20011006, October 2000.
 [9]   Clark, J., "XML Path Language (XPath) Version 1.0",  W3C REC
       REC-xpath-19991116, November 1999.
 [10]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
       Specifications: ABNF", RFC 4234, October 2005.
 [11]  Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
       (S/MIME) Version 3.1 Message Specification", RFC 3851, July
       2004.

11.2. Informative References

 [12]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
       Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
       Session Initiation Protocol", RFC 3261, June 2002.
 [13]  Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and
       J. Peterson, "Presence Information Data Format (PIDF)", RFC
       3863, August 2004.
 [14]  Schulzrinne, H., Gurbani, V., Kyzivat, P., and J. Rosenberg,
       "RPID -- Rich Presence Extensions to the Presence Information
       Data Format (PIDF)", RFC 4480, July 2006.
 [15]  Rosenberg, J., "A Presence Event Package for the Session
       Initiation Protocol (SIP)", RFC 3856, August 2004.
 [16]  Rosenberg, J., "An Extensible Markup Language (XML) Based
       Format for Watcher Information", RFC 3858, August 2004.

Khartabil, et al. Standards Track [Page 21] RFC 4661 XML Based Format for Filtering September 2006

 [17]  Roach, A. B., Campbell, B., and J. Rosenberg, "A Session
       Initiation Protocol (SIP) Event Notification Extension for
       Resource Lists", RFC 4663, September 2006.
 [18]  Rosenberg, J., "Presence Authorization Rules", Work in
       Progress, June 2006.

Khartabil, et al. Standards Track [Page 22] RFC 4661 XML Based Format for Filtering September 2006

Authors' Addresses

 Hisham Khartabil
 Telio
 P.O. Box 1203 Vika
 Oslo
 Norway
 Phone: +47 2167 3544
 EMail: hisham.khartabil@telio.no
 Eva Leppanen
 Nokia
 P.O BOX 785
 Tampere
 Finland
 Phone: +358 7180 77066
 EMail: eva-maria.leppanen@nokia.com
 Mikko Lonnfors
 Nokia
 P.O BOX 321
 Helsinki
 Finland
 Phone: + 358 71800 8000
 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

Khartabil, et al. Standards Track [Page 23] RFC 4661 XML Based Format for Filtering September 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 attempt made to obtain a general license or permission for the use of
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 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Khartabil, et al. Standards Track [Page 24]

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