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 Khartabil, et al. Expires April 23, 2004 [Page 1] Internet-Draft XML Based Format for Filtering October 2003 document format. Table of Contents 1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3 3. Structure of XML-Encoded Filter Criteria . . . . . . . . . 3 3.1 The Root Element . . . . . . . . . . . . . . 4 3.2 The Element . . . . . . . . . . . . . . . . . . . 4 3.3 The Element . . . . . . . . . . . . . . . . . . . . 5 3.3.1 The Element . . . . . . . . . . . . . . . . . 5 3.3.1.1 The "base-element" Attribute . . . . . . . . . . . . . . . 6 3.3.2 The Element . . . . . . . . . . . . . . . . . . 6 3.3.2.1 The "type" Attribute . . . . . . . . . . . . . . . . . . . 7 3.3.2.2 The "level" Attribute . . . . . . . . . . . . . . . . . . 7 3.3.3 The Element . . . . . . . . . . . . . . . . . . 8 3.4 The Element . . . . . . . . . . . . . . . . . . 8 3.4.1 The 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 Element . . . . . . . . . . . . . . . . . . . 9 3.4.3 The 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 Element . . . . . . . . . . . 11 6.2 Filter Criteria Using Element . . . . . . . . . 12 6.3 Filter Criteria Using and Elements . . . 12 6.4 Content Filter Using Namespaces . . . . . . . . . . . . . 13 6.5 Content Filter Using Only 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 Khartabil, et al. Expires April 23, 2004 [Page 2] Internet-Draft XML Based Format for Filtering October 2003 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 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; "". This specification makes use of XML namespaces Khartabil, et al. Expires April 23, 2004 [Page 3] Internet-Draft XML Based Format for Filtering October 2003 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 Root Element The root element of the filter criteria is . The 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 element MUST contain one or more elements. 3.2 The Element The element is used to specify the content of an individual filter. The MUST have an 'id' attribute. The value of the 'id' attribute MUST be unique within the element. The 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 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 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 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 Khartabil, et al. Expires April 23, 2004 [Page 4] Internet-Draft XML Based Format for Filtering October 2003 is 'false'. The element MAY contain a element and MAY contain one or more elements, but MUST contain either the element or the element. 3.3 The Element The 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 element MAY contain a element, one or more elements and one or more elements. However, the element MUST contain at least one element. 3.3.1 The Element The 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 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 element of the value 'open': status/basic="open". 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" Khartabil, et al. Expires April 23, 2004 [Page 5] Internet-Draft XML Based Format for Filtering October 2003 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 Element The element is used to select the content to be delivered. The value of the 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 is "level". The optional "level" attribute is used to select elements related to the element identified in the body of the element. Note that in addition to the content defined using the elements also other mandatory XML items may become selected to make the resulting XML document valid. The following example selects descendants of the element. Thus, it selects the element according to [2]. //tuple/status. If both the and the elements are defined in a content filter, the value of the element relates to the Khartabil, et al. Expires April 23, 2004 [Page 6] Internet-Draft XML Based Format for Filtering October 2003 base element in such a way that the value of the 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 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 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 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: location. 3.3.2.2 The "level" Attribute The "level" attribute is used to select the related elements of the element identified in the element, along with the identified element itself. The following values are pre-defined: 'self', 'ancestor' and 'descendant'. If the attribute is omitted the Khartabil, et al. Expires April 23, 2004 [Page 7] Internet-Draft XML Based Format for Filtering October 2003 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 Element The element is used to define exceptions to the set of XML elements and/or attributes selected by the elements. Thus, those XML elements (including their lower level "child" elements) and/or attributes defined by the element are not delivered. The element has the optional "type" attribute (see the definition of the "type" in Section 3.3.2.1). The element can be used only if one or more element(s) have been included in the same content filter. 3.4 The Element The 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 elements criteria constitute the content to be delivered. The element MAY contain the element, the element or the , 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 element denotes the "AND" operation. This means that updates to a resource that satisfy ALL of the , and elements' criteria within the element constitute the content to be delivered. 3.4.1 The Element The 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 Khartabil, et al. Expires April 23, 2004 [Page 8] Internet-Draft XML Based Format for Filtering October 2003 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 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 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 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 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 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 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 Element The 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". Khartabil, et al. Expires April 23, 2004 [Page 9] Note that if a filter includes both the content filter () part and the element then the definitions of the part SHOULD cover also the added elements, or otherwise the content is delivered without the items defined in the element. 3.4.3 The Element The 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 = value = 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. Khartabil, et al. Expires April 23, 2004 [Page 10] Internet-Draft XML Based Format for Filtering October 2003 6. Examples The XML Schema for the XML document examples is specified in the Section 7. 6.1 Filter Criteria Using 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 elements that have a value "MMS", "SMS" or "IM". The 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: rpid:class="IM" or rpid:class="SMS" or rpid:class="MMS" //tuple //tuple //tuple Another alternative definition is presented below. Note that one of the 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. Khartabil, et al. Expires April 23, 2004 [Page 11] Internet-Draft XML Based Format for Filtering October 2003 class="IM" or class="SMS" or class="MMS" //tuple //tuple 6.2 Filter Criteria Using Element This filter criteria selects the content to be delivered to the subscriber when a certain PIDF [2] tuple changes its status from 'CLOSED' to 'OPEN'. /presence/tuple/status/basic 6.3 Filter Criteria Using and 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. Khartabil, et al. Expires April 23, 2004 [Page 12] Internet-Draft XML Based Format for Filtering October 2003 @status="terminated" and @event="rejected" //watcher //watcher //watcher/@status 6.4 Content Filter Using Namespaces This filter criteria selects XML elements belonging to certain namespaces. urn:ietf:params:xml:ns:cpim-pidf 6.5 Content Filter Using Only Elements This filter criteria selects certain XML elements. Khartabil, et al. Expires April 23, 2004 [Page 13] Internet-Draft XML Based Format for Filtering October 2003 //status //icon /presence/tuple/note //vcard 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. rpid:type="service" or rpid:type="device" //contact //status //status //status rpid:type="service" or rpid:type="device" //tuple //tuple //tuple urn:ietf:params:xml:ns:pidf:cipid Khartabil, et al. Expires April 23, 2004 [Page 14] Internet-Draft XML Based Format for Filtering October 2003 7. XML Schema for Filter Criteria XML Schema Implementation (Normative) XML Schema Definition for Filter Criteria. Khartabil, et al. Expires April 23, 2004 [Page 15] Internet-Draft XML Based Format for Filtering October 2003 Khartabil, et al. Expires April 23, 2004 [Page 16] Internet-Draft XML Based Format for Filtering October 2003 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 , , and 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 Khartabil, et al. Expires April 23, 2004 [Page 17] Internet-Draft XML Based Format for Filtering October 2003 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 Khartabil, et al. Expires April 23, 2004 [Page 18] 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. Khartabil, et al. Expires April 23, 2004 [Page 19] Internet-Draft XML Based Format for Filtering October 2003 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 Khartabil, et al. Expires April 23, 2004 [Page 20] Internet-Draft XML Based Format for Filtering October 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. 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Expires April 23, 2004 [Page 21] Internet-Draft XML Based Format for Filtering October 2003 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Khartabil, et al. Expires April 23, 2004 [Page 22]