Internet Draft A. Beck M. Hofmann Expires: January 2002 Lucent Technologies Document: draft-beck-opes-irml-01.txt July 20, 2001 Category: Informational IRML: A Rule Specification Language for Intermediary Services Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. 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. Abstract OPES intermediary services are a new class of applications running on network edge intermediary devices like caching proxies or dedicated service execution servers. They are described in [2] and [3]. These intermediary services can be executed on behalf of clients or content providers. In order to control the execution of intermediary services, both parties provide service-specific rules which trigger services if rule conditions are met for incoming or outgoing messages. The Intermediary Rule Markup Language (IRML) is an XML-based language that can be used to describe service-specific execution rules. It allows clients and content providers to specify when and how to execute OPES intermediary services. Table of Contents 1 Terminology ....................................................3 2 Problem Description and Goals ..................................3 3 IRML Syntax and Grammar ........................................3 Beck, Hofmann Expires January 2001 [Page 1] Internet Draft IRML July 2001 3.1 The "rulemodule" Element .....................................4 3.1.1 The "owner" Element .........................................4 3.1.2 The "name" Element ..........................................4 3.1.3 The "id" Element ............................................5 3.2 The "protocol" Element .......................................5 3.3 Examples of the "owner", "name", "id", "protocol" Elements ...5 3.4 The "rule" Element ...........................................6 3.4.1 The "property" Element ......................................7 3.4.2 The "action" Element ........................................8 3.4.3 Examples of the "rule", "property" and "action" Elements ....9 4 Order of Service Execution .....................................9 5 Security Considerations .......................................10 6 Acknowledgement ...............................................10 7 References ....................................................10 Author's Addresses................................................11 Appendix - IRML DTD...............................................11 Appendix - Rule Module Examples...................................12 Full Copyright Statement..........................................13 Beck, Hofmann Expires August 2001 [Page 2] Internet Draft IRML July 2001 1 Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [4]. Other terminology used in this document is consistent with that defined and used in [2]. 2 Problem Description and Goals The two parties that may wish to run OPES intermediary services as described in [2] and [3] are clients and content providers. Both parties must be able to express the conditions under which they wish to run a service. A content provider, for instance, may want to adapt its pages for users with small wireless devices. Web users may wish to have certain Web pages translated into a different language. These examples demonstrate the need for rules that tell the OPES intermediary device hosting these services when to run what service. Clients and content providers must provide their rules to the OPES intermediary or OPES admin server. They may also authorize the owner of an OPES intermediary (e.g. an ISP) to set up rules on the OPES intermediary on their behalf. A rule engine on the OPES intermediary device processes rules that apply to incoming requests/outgoing responses in order to determine what service modules need be executed when and in what order. This document defines the Intermediary Rule Markup Language (IRML) in an attempt to create a standard rule format that will be supported by vendors of OPES intermediary devices and by third parties offering OPES service applications. The Intermediary Rule Markup Language defined in this document serves as a standard representation of rules for OPES intermediary services. Since IRML is human-readable it also facilitates the exchange and discussion of these kind of rules between and within groups of rule authors. It is beyond the scope of this document to define a secure and reliable mechanism for transferring rule files to intermediary devices. Likewise, this document does not describe the specifics of how to (efficiently) process rules on the intermediary device. 3 IRML Syntax and Grammar Beck, Hofmann Expires August 2001 [Page 3] Internet Draft IRML July 2001 IRML is an application of XML. Thus, its syntax is governed by the rules of the XML syntax as defined in [5], and its grammar is specified by a DTD, or Document Type Definition. The IRML DTD can be found in Appendix A. Valid and well-formed IRML documents consist of one or more rule modules. Each rule module contains a set of rules and information about the rule module author. Rule modules can be authored by a content provider or by a client (although usually indirectly through an access provider). The rules contained in rule modules each consist of a number of conditions and a number of consequent actions that must be executed if the conditions are met. The conditions within a rule refer to message properties in the request or response message of a given Web transaction. They are met if the property value matches the pattern(s) specified in the rule condition(s). 3.1 The "rulemodule" Element The "rulemodule" element is the root element for all rule modules and MAY/MUST contain the following elements (see also IRML DTD in Appendix A). 3.1.1 The "owner" Element The "owner" element specifies the owner of the rule module. Each rule module can have exactly one owner. Attributes of "owner" Name Values ---------------------------------------------------- class content provider|client The "class" attribute assigns a rule module owner to one of the two types of rule module authors: content providers and clients. 3.1.2 The "name" Element The "name" element contains a descriptive name for the rule module owner. This could be the company name for content providers and a customer login for clients. The name does not have to be unique among rule module owners. Beck, Hofmann Expires August 2001 [Page 4] Internet Draft IRML July 2001 3.1.3 The "id" Element The "id" element contains an identifier for the rule module owner. The identifier MUST be unique within a class of rule module providers. The "id" element determines whether a particular Web transaction is relevant to a rule module and thus, whether the contained rules have to be processed for this Web request/response. For example, a rule module provided by a content provider should only be processed for Web request referring to Web resources owned by this particular content provider. Therefore, if the rule module owner is a content provider, the "id" element MUST contain the domain name(s) of the content provider. If a content provider owns more than one domain and the relevant rule module pertains to more than one of them, the "id" element MAY even contain more than one domain name separated by the "|" character (see "owner" example). The specified domain name(s) MAY also contain a port number. If no port number is specified, then the default port for the specified protocol is assumed, e.g. 80 for HTTP. If the rule module owner is a client, then a unique client identifier, e.g. a customer id, MUST be chosen in order to associate client rule modules with client requests. If an access provider assigns only static IP numbers to its customers, the "id" element can also contain the IP number of the module owner. Otherwise, the dynamic IP addresses of incoming client requests MUST be mapped to the unique client "id" element value in order to determine whether a specific rule module must be processed for a particular client request/server response. 3.2 The "protocol" Element The "protocol" element contains the name of the protocol acronym the rule module pertains to. Although most services operate on HTTP, IRML is not limited to HTTP messages. Any other message-based protocol that fits into the OPES framework can be used. 3.3 Examples of the "owner", "name", "id", "protocol" Elements Yahoo Inc. www.yahoo.com|dir.yahoo.com:8000 http abeck Beck, Hofmann Expires August 2001 [Page 5] Internet Draft IRML July 2001 205.167.45.1 http 3.4 The "rule" Element The "rule element" contains one or more "property" and/or "action" elements. Attributes of "rule" Name Values ---------------------------- processing-point 1|2|3|4 The "processing-point" attribute specifies at which of the four points in figure 1 a rule must be processed by the rule engine on the intermediary device. The four common processing points of an OPES intermediary are further defined in [6]. Implementation architectures for other intermediary devices might define different or additional processing points. Figure 1 shows the typical HTTP data flow between a client, an OPES intermediary (in this case a caching proxy), and an origin server. The four processing points (1-4) represent locations in the round trip message flow where rules can be processed and service modules can be executed. Note that in a caching proxy the message flow may skip points 2 and 3 after point 1 if the requested object can be served from cache. +--------+ +-----------+ +--------+ | |<------|4 3|<------| | | Client | | Caching | | Origin | | | | Proxy | | Server | | |------>|1 2|------>| | +--------+ +-----------+ +--------+ Figure 1: Rule Processing/Service Execution Points Depending on the service type, rules may be processed and services may be executed at any of the four points outlined in figure 1. A virus scanning service for instance could be executed at point 3 in figure 1 in order to scan all Web objects for viruses before they can be stored in the cache. A URL-based request filtering service on the other hand should be executed at point 1 and a language translation service should probably be executed at point 4. Beck, Hofmann Expires August 2001 [Page 6] Internet Draft IRML July 2001 3.4.1 The "property" Element The "property" element contains one or more other "property" elements and one or more "action" elements. "property" elements are conditions, that, if met, will lead to the execution of the service modules specified in the contained "action" elements. Nested "property" elements represent a hierarchical "AND" relationship. This means that an inner "property" condition can only be true, if the outer "property" condition is true and so forth. Attributes of "property" Name Values Default ----------------------------------------------------------- name CDATA type (message|system|service) "message" matches CDATA case-sensitive (yes|no) "no" The "name" attribute specifies the name of the property that is to be matched. The "type" attribute specifies the property type further. By default, properties have the type "message", that is they refer to a request or a response message property so that the specified property name refers to a protocol-specific header name. For HTTP messages for example, the list of protocol-specific header names is defined in [7]. IRML, however, is not limited to the message properties defined in protocol specifications. It also supports user-defined message properties (e.g. user-defined protocol headers). If the property "type" attribute is specified as "system", then the property name refers to system variables that are set by the OPES intermediary. For HTTP messages, IRML defines the following system variables: Property Name Value -------------------------------------------------------------- "request-line" the first line of an HTTP request "response-line" the first line of an HTTP response "request-host" the host name of the origin server "request-path" the relative path of the request URI In addition to these HTTP-specific headers, IRML also defines the following general system property variables: Property Name Value -------------------------------------------------------------- "system-date" a timestamp using the Internet date/time format as defined in [8] Beck, Hofmann Expires August 2001 [Page 7] Internet Draft IRML July 2001 "client-ip" the IP number of the user agent The "system-date" and "client-ip" variable MUST be supported by all OPES intermediaries. If the OPES intermediary supports HTTP, it MUST also support the above listed HTTP system properties. If the property "type" attribute is specified as "service", then the property name refers to service-specific environment variables that can be set and modified by OPES service modules. These can be used by OPES service modules to maintain state information beyond a particular session. If these service variables are referenced in IRML rule conditions, then OPES service modules can dynamically adapt the conditions that lead to the invocation of OPES services without altering the actual rule module. Service-specific variables can also be used for the communication between different OPES modules, e.g. if one service module sets a state variable that is subsequently read by another service module. The "matches" attribute specifies the pattern against which the property value MUST be matched by the rule engine on the intermediary device. The "matches" pattern MUST be a regular expression compliant with the regular expression syntax as defined in [9]. If needed, the double-quote character (") MUST be represented in any attribute value as """ (as specified in [5]). The "case-sensitive" attribute specifies whether the matching of the specified pattern must be performed case sensitive or not. The default value for this attribute is "no" meaning that pattern matching is case insensitive unless otherwise specified. If a "rule" element contains an "action" element outside of a "property" element, then the specified action must be performed for all messages that pass through the specified processing point. A user profiling service, for example, may have to be triggered for all user requests. 3.4.2 The "action" Element The "action" element identifies the OPES service module that is to be executed on the intermediary device or a dedicated service execution server. The "action" element does not, however, specify a specific instance of the OPES service module, e.g. a specific installation on a specific server. Instead, the OPES intermediary can resolve the identified OPES service to a specific instance at run-time in order to accomodate for system or network conditions, e.g. the current system load on a particular remote callout server. Beck, Hofmann Expires August 2001 [Page 8] Internet Draft IRML July 2001 The "action" element MUST contain an absolute URI that follows the URI syntax as defined in [10] and uniquely identifies an OPES service module including its version. The URI scheme to be used to identify OPES services is "opes". Note that although an OPES URI contains a hostname, it only serves as a unique identifier for a specific OPES service module. Any arguments to OPES service modules MAY be passed as part of the service module name using the standard "?"-encoding of attribute- value pairs used in HTTP [7]. Only one OPES service URI MAY be specified per "action" element. A "property" element, however, MAY contain several "action" elements. 3.4.3 Examples of the "rule", "property" and "action" Elements opes://logmaker.com/requestlog-v1.0 opes://altavista.com/babelfish?mode=quick opes://mcaffee.com/scan?mode=remove 4 Order of Service Execution The order in which service modules on the intermediary device are executed may change the final result of OPES service processing. For example, an a content analyzer/filtering service executed against the result of a Web page translation service may produce a different result than a reverse execution order. Beck, Hofmann Expires August 2001 [Page 9] Internet Draft IRML July 2001 Up to two rule modules may have to be processed by an OPES intermediary per Web transaction. The order in which these rule modules are processed MUST reflect the order in which request/response messages pass by rule module authors. This means that for incoming requests at points 1 and 2 in figure 1, the order MUST be: 1. Client rule module 2. Content provider rule module For outgoing responses at points 3 and 4, the order MUST be: 1. Content provider rule module 2. Client rule module Within a single rule module, the intermediary device MUST process and execute all rules and actions IN THE ORDER THEY ARE SPECIFIED in the rule module (both within "property" and "rule" elements). If the rule processor determines that multiple actions must be executed for any given transaction, it MUST take into account that message property values may be modified by the execution of OPES service modules. This may require waiting for the completion of a triggered service module before rule conditions of subsequent rule can be evaluated. 5 Security Considerations Although beyond the scope of this document, it is clearly necessary to define a secure mechanism for transferring rule modules to intermediary devices. This will include authenticating and authorizing rule module owners and OPES intermediaries or admin servers. The integrity of rule modules must also be guaranteed. Also, a security context must be established on the OPES intermediary device for each rule module to ensure that rule modules may not execute service modules or call library functions on the intermediary without without being authorized to do so. 6 Acknowledgement The authors would like to thank all active participants in the OPES mailing list for their thought-provoking discussion, and many of the ideas, suggestions that have been incorporated into the document. Especially we want to ackowledge the following people for their helpful contributions: Lily Yang, Christian Maciocco, Mark Nottingham, and Michael Condry. 7 References Beck, Hofmann Expires August 2001 [Page 10] Internet Draft IRML July 2001 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996 2 Tomlinson, G., et al., "A Model for Open Pluggable Edge Services," Work in Progress Internet Draft: draft-tomlinson-opes- model-00.txt, July 2001. 3 McHenry, S., et al., "OPES Use Cases and Deployment Scenarios", Work in Progress Internet Draft: draft-mchenry-opes-deployment- scenarios-00.txt, July 2001 4 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", Request for Comments 2119, Harvard University, March 1997 5 Bray, T., et al., Extensible Markup Language (XML) 1.0 (Second Edition), http://www.w3.org/TR/2000/REC-xml-20001006, October 2000 6 Rafalow, L., et al., "Policy Requirements for Edge Services", Work in Progress, Internet Draft draft-rafalow-opes-policy- requirements-00.txt, July 2001 7 Fielding, R., et al., "Hypertext Transfer Protocol -- HTTP/1.1", Request for Comments 2616, June 1999 8 Klyne, G., et al., "Date and Time on the Internet: Timestamps", Work in Progress, Internet Draft "draft-ietf-impp-datetime- 04.txt", July 2001 9 ISO/IEC DIS 9945-2:1992, Information technology - Portable Operating System Interface (POSIX) - Part 2: Shell and Utilities (IEEE Std 1003.2-1992); X/Open CAE Specification, Commands and Utilities, Issue 4, 1992 10 Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax and Semantics", Request for Comments 2396, August 1998 Author's Addresses Andre Beck Markus Hofmann Bell Labs Research Lucent Technologies 101 Crawfords Corner Rd. Holmdel, NJ 07733 Phone: (732) 332-5983 Email: {abeck, hofmann}@bell-labs.com Appendix - IRML DTD Beck, Hofmann Expires August 2001 [Page 11] Internet Draft IRML July 2001 Appendix - Rule Module Examples Content Provider Rule Module Example for Advertisement Insertion Service Lucent Technologies www.lucent.com http opes://doubleclick.net/insertad Client Rule Module Example for Language Translation and Virus Scanning Service Markus Hofmann 2324264 Beck, Hofmann Expires August 2001 [Page 12] Internet Draft IRML July 2001 http opes://mcaffee.com/scan?mode=remove Document language is probably not German -> Page needs to be translated --> opes://altavista.net/translate Content Provider Rule Module Example for Content Adaptation Service for Wireless Web Access Devices Yahoo Inc. www.yahoo.com http opes://wapgateway.nl/transcode Full Copyright Statement Copyright (C) The Internet Society (2000). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any Beck, Hofmann Expires August 2001 [Page 13] Internet Draft IRML July 2001 kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. 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