SIMPLE H. Khartabil
Internet-Draft E. Leppanen
Expires: February 9, 2005 M. Lonnfors
J. Costa-Requena
Nokia
August 11, 2004
An Extensible Markup Language (XML) Based Format for Event
Notification Filtering
draft-ietf-simple-filter-format-02
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Copyright Notice
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Abstract
Filtering is a mechanism for defining the preferred content to be
delivered and for specifying the rules for when the content should be
delivered. 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 document format.
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The filtering mechanism is expected to be particularly valuable and
primarily applicable to users of mobile wireless access devices.
Table of Contents
1. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Structure of XML-Encoded SIMPLE Filter . . . . . . . . . . . . 3
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 . . . . . . . . . . . . . . . . . . . . 5
3.5.1 The <include> Element . . . . . . . . . . . . . . . . 6
3.5.2 The <exclude> Element . . . . . . . . . . . . . . . . 6
3.5.3 The 'type' Attribute . . . . . . . . . . . . . . . . . 7
3.6 The <trigger> Element . . . . . . . . . . . . . . . . . . 7
3.6.1 The <changed> Element . . . . . . . . . . . . . . . . 7
3.6.1.1 The 'from' Attribute . . . . . . . . . . . . . . . 8
3.6.1.2 The 'to' Attribute . . . . . . . . . . . . . . . . 8
3.6.1.3 The 'by' Attribute . . . . . . . . . . . . . . . . 8
3.6.1.4 Combination of Attributes . . . . . . . . . . . . 8
3.6.2 The <added> Element . . . . . . . . . . . . . . . . . 9
3.6.3 The <removed> Element . . . . . . . . . . . . . . . . 9
4. Syntax for Referencing XML Items and Making Logical
Expressions . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1 Filter Criteria Using <what> Element . . . . . . . . . . . 11
5.2 Filter Criteria Using <trigger> Element . . . . . . . . . 12
5.3 Filter Criteria Using <what> and <trigger> Elements . . . 12
5.4 Content Filter Using Namespaces . . . . . . . . . . . . . 13
5.5 Content Filter Using Only <include> Elements . . . . . . . 14
5.6 Two Content Filters as Filter Criteria . . . . . . . . . . 14
6. XML Schema for Filter Criteria . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8.1 application/simple-filter+xml MIME TYPE . . . . . . . . . 18
8.2 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:simple-filter . . . . . . . . . . . 19
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1 Normative References . . . . . . . . . . . . . . . . . . . . 20
10.2 Informative References . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . 23
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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.
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 7.
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 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 [13] the change in the value of the
<status> element.
The functionality of the filtering regarding the SIP event
notifications is specified in [3].
3. Structure of XML-Encoded SIMPLE Filter
The simple-filter is an XML document [8] that MUST be well-formed and
SHOULD be valid. The simple-filter documents MUST be based on XML
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1.0 and MUST be encoded using UTF-8.
The namespace identifier for elements defined by this specification
is a URN [5], using 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 on.
3.1 MIME Type for simple-filter Document
The MIME type for the simple-filter document is "application/
simple-filter+xml". Any transport protocol that is used to carry the
filters that also carries payload type information MUST identify the
payload as MIME type "simple-filter+xml" (for example: a Content-Type
header).
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 The <filter-set> element may contain one <ns-bindings> elements.
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
the syntax in Section 4. 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.
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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 an 'uri' attribute. The value of the 'uri'
attribute is the URI of the resource which the filter applies to.
The <filter> MAY have an 'domain' attribute. The value of the
'domain' attribute is the domain of the resources that the filter
applies to. The 'uri' attribute and the 'domain' attribute MUST NOT
appear together in a filter.
The URI of the resource is useful in cases where the 'event list'
extension [15] 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 who's 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 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> MAY have a 'enabled' attribute which 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 MUST contain either the <what>
element or the <trigger> element.
3.5 The <what> Element
The <what> element is used to specify the content to be delivered to
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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. I.e. each <include> element
contents adds an element or attribute to the resulting XML document.
When more than one <exclude> element has been defined, each value it
each <exclude> element 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
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.
The syntax defined in Section 4 (see the definition of "selection".)
MUST be used. The following example selects the <status> element
defined in the PIDF [11]. This results in the selection of the
<status> element as well as all the ancestors of <status>. I.e.
<basic> and <tuple>.
<include type="xpath">//tuple/status</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,
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.
The <exclude> element has the optional 'type' attribute (see the
definition of the 'type' in Section 3.5.3).
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Note that the resulting XML document MUST be valid. Therefore, if
applying the <exclude> element value to an XML document results in an
invalid document according to the schema, the mandatory elements and/
or attributes must be re-introduced into the resulting XML document
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 4.
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 4 that selects and
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.
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 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.
3.6.1 The <changed> Element
The <changed> element is used to identify the XML element or
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attribute, from the package specific XML document, who's value MUST
change, compared to 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 last XML document that was
selected for delivery to that specific subscriber before the filter
was applied to it. The XML element or attribute MUST be expressed
using the syntax defined in Section 4 for the "reference" ABNF.
The <changed> element MAY contain the 'from' attribute, 'to'
attribute, 'by' attribute, or any combination of the three. The
absence of all 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 with a case sensitive string
comparson. This applies to elements or attributes that don't carry a
numerical value. Numerical values are considered changed when the
value has incread or decreased.
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.
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 the value indicated by this
attribute from a different value. I.e. The 'by' attribute applies
only to numerical values and indicates a delta with respect 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 lower
value.
3.6.1.4 Combination of Attributes
Any combination of the 'from', 'to', and 'by' attributes in the
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<changed> element is possible. For example, if the 'from' attribute
was combined with the '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 '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 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 MUST be expressed using the syntax defined in Section 4 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 cover also the added elements, or otherwise the content is
delivered without the items defined in the <added> element.
3.6.3 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 MUST be expressed using the syntax
defined in Section 4 for the "reference" ABNF.
4. 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
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.
I.e. If a filter including a element evaluates to 2 elements, both
elements are included as a result.
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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",
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 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"]
o Selecting an element by using two XML elements as a condition :
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* //tuple[status/basic="open" and type="device"]
o Selecting an attribute :
* //watcher/@duration-subscribed
According to the ABNF above, the XPATH-like expression cannot and
MUST NOT identify more than one element or attribute. However, in
some cases due to the design of the XML schema, the expression
results in identifying more than one element with the same name (the
XPATH expression does not uniquely identify an element at every
step). In other cases, it is possible that more than one element or
attribute is identified due to the condition part resulting in the
the selection of more than one element or attribute with the same
name. In those cases, all elements identified are selected.
5. Examples
The XML Schema for the XML document examples is specified in the
Section 6.
5.1 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 [12] as an extension to PIDF [11].
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<?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-tuple"/>
</ns-bindings>
<filter id="123" uri="sip:presentity@domain.com">
<what>
<include type="xpath">
//pidf:tuple[rpid:class="IM" or rpid:class="SMS"
or rpid:class="MMS"]/pidf:status/pidf:basic
</include>
</what>
</filter>
</filter-set>
5.2 Filter Criteria Using <trigger> Element
A user requires to get informed when his colleague becomes available
by some communication mean(s). The user gets the full presence state
of the colleague when a certain PIDF [11] 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@domain.com">
<trigger>
<changed from="CLOSED" to="OPEN">
/pidf:presence/pidf:tuple/pidf:status/pidf:basic
</changed>
</trigger>
</filter>
</filter-set>
5.3 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 [14] to be sent
when a subscription status has changed to "pending" or "waiting". In
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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@domain.com">
<what>
<include>
//wi:watcher[@status="pending" or @status="waiting"]
</include>
</what>
<trigger>
<changed to="pending">
//wi:watcher/@status
</changed>
</trigger>
<trigger>
<changed to="waiting">
//wi:watcher/@status
</changed>
</trigger>
</filter>
</filter-set>
5.4 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@domain.com">
<what>
<include type="namespace">
urn:ietf:params:xml:ns:pidf
</include>
</what>
</filter>
</filter-set>
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5.5 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.
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" >
<ns-bindings>
<ns-binding prefix="game-ext"
urn="urn:ietf:params:xml:ns:game-ext"/>
</ns-bindings>
<filter id="123">
<what>
<include>
//pidf:tuple/pidf:status[game-ext:label="game-X"]
</include>
</what>
</filter>
</filter-set>
5.6 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.
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<?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-tuple"/>
</ns-bindings>
<filter id="8439" uri="sip:buddies@domain.com">
<what>
<include>
//pidf:tuple[rpid:class="service"]/pidf:status/pidf:basic
</include>
</what>
</filter>
<filter id="999" uri="sip:bob@domain.com">
<what>
<include type="namespace">
urn:ietf:params:xml:ns:pidf
</include>
<exclude>
//pidf:tuple/pidf:note
</exclude>
</what>
</filter>
</filter-set>
6. 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">
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<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: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>
<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"/>
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</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>
</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"/>
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<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>
7. Security Considerations
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
MUST establish a limit on the number of occurrences of the <what>,
<changed>, <added> and <removed> elements allowed in the filters. A
default limit of 20 is RECOMMENDED, however, servers MAY raise or
lower the limit depending upon their specific engineered capacity.
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 [2] MUST be
followed along with package specific security.
8. 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 [7].
8.1 application/simple-filter+xml MIME TYPE
MIME media type: application
MIME subtype name: simple-filter+xml
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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 7 of this document.
Interoperability considerations: none.
Published specification: This document.
Applications which use this media type: This document type has been
used to support SIP based Event notification framework and its
packages.
Additional information:
Magic number: None
File extension: .cl or .xml
Macintosh file type code: "TEXT"
Personal and email address for further information: Hisham Khartabil
(hisham.khartabil@nokia.com)
Intended Usage: COMMON
Author/change controller: The IETF
8.2 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:simple-filter
This section registers a new XML namespace, as per guidelines in URN
document [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@nokia.com)
XML:
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BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Event Notification Filtering Namespace</title>
</head>
<body>
<h1>Namespace for Event Notification Filtering</h1>
<h2>application/simple-filter+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
9. Acknowledgements
The authors would like to thank Jonathan Rosenberg, Henning
Schulzrinne, Tim Moran, Jari Urpalainen, Sreenivas Addagatla,
Miguel-Angel Garcia Martin, Mary Barnes and Paul Kyzivat for their
valuable input and comments.
10. References
10.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[3] Khartabil, H., "Functional Description of Event Notification
Filtering", draft-simple-filter-funct-00.txt (work in
progress), February 2004.
[4] Mealling, M., "The IETF XML Registry", RFC 3688, January 2004.
[5] Moats, R., "The URN Syntax", RFC 2141, May 1997.
[6] Moats, R., "The URN Namespace for IETF Documents", RFC 2648,
August 1999.
[7] Murata, M., "XML Media Types", RFC 3023, March 1997.
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[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., "Augmented BNF for Syntax Specifications: ABNF",
RFC 2234, November 1997.
10.2 Informative References
[11] Sugano, H., "CPIM Presence Information Data Format",
draft-ietf-impp-cpim-pidf-08.txt (work in progress), May 2003.
[12] Schulzrinne, H., "RPID -- Rich Presence Information Data
Format", draft-ietf-simple-rpid-00.txt (work in progress), May
2004.
[13] Rosenberg, J., "Session Initiation Protocol (SIP) Extensions
for Presence", RFC RFC3856, July 2004.
[14] Rosenberg, J., "An Extensible Markup Language (XML) Based
Format for Watcher Information", RFC RFC3858, July 2004.
[15] Roach, A., "A Session Initiation Protocol (SIP) Event
Notification Extension for Resource Lists",
draft-ietf-simple-event-list-04.txt, June 2003.
Authors' Addresses
Hisham Khartabil
Nokia
P.O. Box 321
Helsinki
Finland
Phone: +358 7180 76161
EMail: hisham.khartabil@nokia.com
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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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