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SIMPLE H. Khartabil
Internet-Draft M. Lonnfors
Expires: April 23, 2004 J. Costa-Requena
E. Leppanen
Nokia
October 24, 2003
An Extensible Markup Language (XML) Based Format for Event
Notification Filtering
draft-khartabil-simple-filter-format-01
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 April 23, 2004.
Copyright Notice
Copyright (C) The Internet Society (2003). 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 <condition> Element . . . . . . . . . . . . . . . . . 5
3.3.1.1 The "base-element" Attribute . . . . . . . . . . . . . . . 6
3.3.2 The <include> Element . . . . . . . . . . . . . . . . . . 6
3.3.2.1 The "type" Attribute . . . . . . . . . . . . . . . . . . . 7
3.3.2.2 The "level" Attribute . . . . . . . . . . . . . . . . . . 7
3.3.3 The <exclude> Element . . . . . . . . . . . . . . . . . . 8
3.4 The <trigger> Element . . . . . . . . . . . . . . . . . . 8
3.4.1 The <changed> Element . . . . . . . . . . . . . . . . . . 8
3.4.1.1 The "changed-from" Attribute . . . . . . . . . . . . . . . 9
3.4.1.2 The "changed-to" Attribute . . . . . . . . . . . . . . . . 9
3.4.1.3 The "changed-by" Attribute . . . . . . . . . . . . . . . . 9
3.4.1.4 Combination of Attributes . . . . . . . . . . . . . . . . 9
3.4.2 The <added> Element . . . . . . . . . . . . . . . . . . . 9
3.4.3 The <removed> Element . . . . . . . . . . . . . . . . . . 10
4. Syntax for Referencing XML Items and Making Logical
Expressions . . . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . 10
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1 Filter Criteria Using <what> Element . . . . . . . . . . . 11
6.2 Filter Criteria Using <trigger> Element . . . . . . . . . 12
6.3 Filter Criteria Using <what> and <trigger> Elements . . . 12
6.4 Content Filter Using Namespaces . . . . . . . . . . . . . 13
6.5 Content Filter Using Only <Include> Elements . . . . . . . 13
6.6 Two Content Filters as Filter Criteria . . . . . . . . . . 14
7. XML Schema for Filter Criteria . . . . . . . . . . . . . . 15
8. Security Requirements . . . . . . . . . . . . . . . . . . 17
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 18
10. Changes from version 00 . . . . . . . . . . . . . . . . . 18
References . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 20
Intellectual Property and Copyright Statements . . . . . . 21
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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 'eventlist'
extension [7] is used with a package and different filters are
defined for one or more members of the list. The 'uri' attribute in
the <filter> element identifies either the URI of the list (or nested
sub-list) or the URI of an individual member within the list to whom
that specific filter applies. If the <filter> does not contain the
'uri' attribute, the filter applies to all the members in the list
unless a member of the list has its own filter attributed by the
'uri' attribute.
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
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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 a <condition> element, one or more
<include> elements and one or more <exclude> elements. However, the
<what> element MUST contain at least one <include> element.
3.3.1 The <condition> Element
The <condition> element is used to select "base elements" using
values of XML elements or XML attributes related to the base
elements. The base element is defined by a mandatory XML attribute
("base-element"). The value of the <condition> element consists of
comparison and logical expressions that has a Boolean outcome. The
syntax for the expressions is defined in Section 4 (see the
definition of the "expression"). The base element is selected if the
expression is positive.
The following example selects the tuples that have a <basic> element
of the value 'open':
<condition base-element="//tuple">status/basic="open"</condition>.
A couple of example expressions are listed below:
o Comparison expressions using XML elements:
* /status/basic="open"
* */basic="open"
o Comparison expressions using XML attributes:
* @duration-subscribed<500
* @event="rejected"
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o Logical expressions using values of two XML elements:
* status/basic="open" and type="device".
3.3.1.1 The "base-element" Attribute
The "base-element" attribute defines the base element selected by the
expression. The "base-element" attribute is used to identify the
element itself or an ancestor element of the XML element or attribute
that used in the expression. The syntax of the value of the
"base-element" is defined in Section 4 (see the definition of the
"reference").
Examples of values of the "base-element" attribute are listed as
follows:
o //tuple
o /presence/tuple
o //*
o /*/tuple.
3.3.2 The <include> Element
The <include> element is used to select the content to be delivered.
The value of the <include> element depends on the "type" attribute.
The value is allowed to be a reference to an XML element or
attribute, a namespace or another value related to the "type"
attribute. Another XML attribute in the <include> is "level". The
optional "level" attribute is used to select elements related to the
element identified in the body of the <include> element.
Note that in addition to the content defined using the <include>
elements also other mandatory XML items may become selected to make
the resulting XML document valid.
The following example selects descendants of the <status> element.
Thus, it selects the <basic> element according to [2].
<include type="xml-element" level="descendant">//tuple/status</
include>.
If both the <condition> and the <include> elements are defined in a
content filter, the value of the <include> element relates to the
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base element in such a way that the value of the <include> element
MUST be either the defined base element or one of the lower level
("child") elements of the base element.
3.3.2.1 The "type" Attribute
The "type" attribute is used to describe the value of the <include>
element. The following values are pre-defined: 'xml-element',
'namespace' and 'token'. Other values of the "type" attribute may be
defined later. The "type" attribute is optional, and, if omitted, the
default value is 'xml-element'.
The 'xml-element' is used when the <include> element contains a
reference of an XML element or attribute. Section 4 defines the
syntax for the reference (see the definitions of the "reference" for
referencing the XML elements and "attr-reference" for referencing the
XML attributes).
Example references are listed as follows:
o Referencing XML elements giving the full hierarchical path: /
presence/tuple/status/basic
o Referencing XML elements from any level by its name: //basic
o Referencing XML attributes of an XML element: //watcher/
@duration-subscribed
o Referencing XML attributes of any element: //@expiration.
The "namespace" value is used when the <include> element contains a
value of a namespace. The value is the URI of the namespace.
The "token" is used to define the content by a value referring to a
certain pre-defined set of elements (e.g., elements which are
semantically close to each other) supported by a entity intepreting
the filter.
Example: <include type="token">location</include>.
3.3.2.2 The "level" Attribute
The "level" attribute is used to select the related elements of the
element identified in the <include> element, along with the
identified element itself. The following values are pre-defined:
'self', 'ancestor' and 'descendant'. If the attribute is omitted the
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default value is 'self'.
Note that only the 'self' value makes sense to the include
definitions of the types 'namespace' and 'token'.
The 'self' value indicates the selection of the given XML element.
The 'ancestor' value indicates the selection of the parent elements
of the given XML element. The 'descendant' value indicates the
selection of the sub-tree ("child elements") of the given XML
element. The Section 4 defines the syntax for referencing the XML
element.
3.3.3 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.
The <exclude> element has the optional "type" attribute (see the
definition of the "type" in Section 3.3.2.1).
The <exclude> element can be used only if one or more <include>
element(s) have been included 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
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attribute is indicated using the syntax defined in Section 4 for the
"reference" and "attr-reference". The indication MUST only point to
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
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" and "attr-reference".
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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" and "attr-reference".
4. Syntax for Referencing XML Items and Making Logical Expressions
The ABNF [18] is used to describe the syntax for the references and
expressions. The syntax is defined to be XPATH [17] 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 [17]. The "abbreviated syntax" of the "node test" is used in the
references ("reference" and "attr-reference"). The expression in the
syntax relates to the predicate, comparision and logical expressions
of the XPATH. The square brackets of predicate expression are left
out.
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 = "/" 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.
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6. Examples
The XML Schema for the XML document examples is specified in the
Section 7.
6.1 Filter Criteria Using <what> Element
This example shows two ways for defining a content filter where the
whole content and upper level elements of the tuples of the presence
information 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 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"
package="presence">
<filter id="mess" uri="sip:presentity@domain.com">
<what>
<condition base-element="//tuple" type="xml-element">rpid:class="IM" or rpid:class="SMS" or rpid:class="MMS"
</condition>
<include level="self" type="xml-element">//tuple</include>
<include level="descendant">//tuple</include>
<include level="ancestor">//tuple</include>
</what>
</filter>
</filter-set>
Another alternative definition is presented below. Note that one of
the <include> elements is omitted which means that it is assumed that
the data format (PIDF [2]) mandates, e.g., the upper level elements
of the selected tuples to be delivered.
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<?xml version="1.0" encoding="UTF-8"?>
<filter-set xmlns="urn:ietf:params:xml:ns:simple-filter"
<filter id="mess">
<what>
<condition base-element="//tuple">class="IM" or class="SMS" or class="MMS"</condition>
<include>//tuple</include>
<include level="descendant">//tuple</include>
</what>
</filter>
</filter-set>
6.2 Filter Criteria Using <trigger> Element
This filter criteria 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">
<filter id="open_mean" uri="sip:presentity@domain.com">
<trigger>
<changed changed-from="CLOSED" changed-to="OPEN">/presence/tuple/status/basic</changed>
</trigger>
</filter>
</filter-set>
6.3 Filter Criteria Using <what> and <trigger> Elements
This filter criteria selects watcher information notifications [8] to
be sent when the pending subscription status has changed from
"pending" to "terminated". In the notification, only the watchers
that have a status of "terminated" and an event of "rejected" are
included.
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<?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>
<condition base-element="//watcher">
@status="terminated" and @event="rejected"
</condition>
<include>//watcher</include>
<include level="ancestor">//watcher</include>
</what>
<trigger>
<changed changed-from="pending" changed-to="terminated">//watcher/@status</changed>
</trigger>
</filter>
</filter-set>
6.4 Content Filter Using Namespaces
This filter criteria selects XML elements belonging to certain
namespaces.
<?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:cpim-pidf
</include>
</what>
</filter>
</filter-set>
6.5 Content Filter Using Only <Include> Elements
This filter criteria selects certain XML elements.
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<?xml version="1.0" encoding="UTF-8"?>
<filter-set xmlns="urn:ietf:params:xml:ns:simple-filter"
package="presence">
<filter id="filter-abc">
<what>
<include>//status</include>
<include>//icon</include>
<include>/presence/tuple/note</include>
<include>//vcard</include>
</what>
</filter>
</filter-set>
6.6 Two Content Filters as Filter Criteria
This filter criteria defines two content filters: the first one to be
used for a list of "buddies" and the second one to get more
information about one of the friends. The PIDF extension elements
defined in [4] are filtered out.
<?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">
<filter id="8439" uri="sip:buddies@domain.com">
<what>
<condition base-element="//tuple">rpid:type="service" or rpid:type="device"
</condition>
<include>//contact</include>
<include>//status</include>
<include level="descendant">//status</include>
<include level="ancestor">//status</include>
</what>
</filter>
<filter id="999" uri="sip:friendX@domain.com">
<what>
<condition base-element="//tuple">rpid:type="service" or rpid:type="device"
</condition>
<include>//tuple</include>
<include level="ancestor">//tuple</include>
<include level="descendant">//tuple</include>
<exclude type="namespace">urn:ietf:params:xml:ns:pidf:cipid</exclude>
</what>
</filter>
</filter-set>
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7. XML Schema for Filter Criteria
XML Schema Implementation (Normative)
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema targetNamespace="urn:ietf:params:xml:ns:simple-filter"
xmlns="urn:ietf:params:xml:ns:simple-filter"
xmlns:xsd=http://www.w3.org/2001/XMLSchema/>
<xsd:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"> <!--lang -->
<xsd:annotation>
<xsd:documentation xml:lang="en">
XML Schema Definition for Filter Criteria.
</xsd:documentation>
</xsd:annotation>
<xsd:element name="filter-set" type="FilterSetType"/>
<xsd:complexType name="FilterSetType">
<xsd:sequence>
<xsd:element name="filter" type="FilterType"
minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
<xsd:attribute name="package" type="xsd:string" use="optional"/>
</xsd:complexType>
<!-- A filter corresponds to the URI indicated by its "uri" attribute. The URI defines the user or a list of users. -->
<xsd:complexType name="FilterType">
<xsd:sequence>
<xsd:element name="what" type="WhatType" minOccurs="0" maxOccurs="1"/>
<xsd:element name="trigger" type="TriggerType" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
<xsd:attribute name="id" type="xsd:string" use="required"/>
<xsd:attribute name="uri" type="xsd:anyURI" use="optional/>
<xsd:attribute name="remove" type="xsd:boolean" default="false" use="optional"/>
</xsd:complexType>
<xsd:complexType name="WhatType">
<xsd:sequence>
<xsd:element name="condition" type="CondType" minOccurs="0" maxOccurs="unbounded"/>
<xsd:element name="include" type="InclType" minOccurs="1" maxOccurs="unbounded"/>
<xsd:element name="exclude" type="ExclType" minOccurs="0" maxOccurs="unbounded"/>
<xsd:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
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<xsd:complexType name="CondType">
<xsd:simpleContent>
<xsd:extension base="xsd:string">
<xsd:attribute name="base-element" type="xsd:string" use="required"/>
<xsd:anyAttribute namespace="##other" processContents="lax" use="optional"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:complexType name="InclType">
<xsd:simpleContent>
<xsd:extension base="xsd:string">
<xsd:attribute name="level" type="LevelType" default="self" use="optional"/>
<xsd:attribute name="type" type="TypeType" default="xml-element" use="optional"/>
<xsd:anyAttribute namespace="##other" processContents="lax" use="optional"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:complexType name="ExclType">
<xsd:simpleContent>
<xsd:extension base="xsd:string">
<xsd:attribute name="type" type="TypeType" default="xml-element" use="optional"/>
<xsd:anyAttribute namespace="##other" processContents="lax" use="optional"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<!--xsd:simpleType name="Base-elemType">
<xsd:restriction base="xs:string">
<xsd:enumeration value="current">
<xsd:enumeration value="tuple">
<xsd:enumeration value="watcher">
</xsd:restriction>
</xsd:complexType -->
<xsd:simpleType name="LevelType">
<xsd:restriction base="xs:string">
<xsd:enumeration value="self">
<xsd:enumeration value="ancestor">
<xsd:enumeration value="descendant">
</xsd:restriction>
</xsd:complexType>
<xsd:simpleType name="TypeType">
<xsd:restriction base="xs:string">
<xsd:enumeration value="xml-element">
<xsd:enumeration value="namespace">
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<xsd:enumeration value="token">
</xsd:restriction>
</xsd:complexType>
<xsd:complexType name="TriggerType">
<xsd:sequence>
<xsd:element name="changed" type="ChangedType" minOccurs="0" maxOccurs="unbounded"/>
<xsd:element name="added" type="xsd:string" minOccurs="0" maxOccurs="unbounded"/>
<xsd:element name="removed" type="xsd:string" minOccurs="0" maxOccurs="unbounded"/>
<xsd:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<xs:complexType name="ChangedType">
<xs:simpleContent>
<xs:extension base="xds:string">
<xs:attribute name="changed-from" type="xsd:anySimpleType" use="optional"/>
<xs:attribute name="changed-to" type="xsd:anySimpleType" use="optional"/>
<xs:attribute name="changed-by" type="xsd:decimal" use="optional"/>
<xsd:anyAttribute namespace="##other" processContents="lax" use="optional"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xsd: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
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
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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.
10. Changes from version 00
o Usage of exact XPATH support restricted (XPATH compatible syntax
still used).
o New solution for the content filter. Examples and XML Schema
updated accordingly.
o ABNF based syntax for data referencing and expressions added.
o More examples added.
o Terminology harmonized and references updated.
o Minor updates concerning the triggering part.
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
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Internet-Draft XML Based Format for Filtering October 2003
Notification Extension for Resource Lists",
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-02.txt (work in progress),
August 2003.
[10] Kiss, K., "Requirements for Filtering of Watcher Information",
draft-ietf-simple-winfo-filter-reqs-00.txt (work in progress),
April 2003.
[11] Khartabil, H., "Functional Description of Event Notification
Filtering", draft-khartabil-simple-filter-funct-00.txt (work
in progress), May 2003.
[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
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
Eva Leppanen
Nokia
P.O BOX 785
Tampere
Finland
Phone: +358 7180 77066
EMail: eva-maria.leppanen@nokia.com
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Khartabil, et al. Expires April 23, 2004 [Page 22]
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