- From the SweetRules Version 2.1 Announcement
- About the Rule Markup Initiative
- RuleML Initiative and Web Services Modeling Ontology (WSMO) Working Group
- About SemWebCentral
- W3C Workshop on Rule Languages for Interoperability
- Principal References
The developers of the SweetRules tools for semantic web rules and ontologies have announced a version 2.1 release of the software at SemWebCentral under the LGPL open source license. Featuring new support for rule-triggered WSDL Web Services, SweetRules is described as the first open source platform for semantic web business rules.
SweetRules is designed around the Rule Markup Language (RuleML), an emerging XML/RDF standard for semantic web rules, and supports the OWL standard for semantic web ontologies. SweetRules also supports the closely related Semantic Web Rule Language (SWRL), essentially an expressive subset of RuleML rules.
The RuleML Initiative is working on an XML-based markup language "that permits Web-based rule storage, interchange, retrieval, and firing/application. RuleML covers the entire rule spectrum, from derivation rules to transformation rules to reaction rules. RuleML can thus specify queries and inferences in Web ontologies, mappings between Web ontologies, and dynamic Web behaviors of workflows, services, and agents. RuleML is about rule interoperation between industry standards (such as JSR 94, SQL'99, OCL, BPMI, WSFL, XLang, XQuery, RQL, OWL, DAML-S, and ISO Prolog) as well as established systems (CLIPS, Jess, ILOG JRules, Blaze Advisor, Versata, MQWorkFlow, BizTalk, Savvion, etc.)."
The W3C Web Ontology Language (OWL) has been developed as part of the Semantic Web Activity. Ontologies "are usually expressed in a logic-based language, so that detailed, accurate, consistent, sound, and meaningful distinctions can be made among the classes, properties, and relations. The OWL Web Ontology Language is designed for use by applications that need to process the content of information instead of just presenting information to humans. OWL facilitates greater machine interpretability of Web content than that supported by XML, RDF, and RDF Schema (RDF-S) by providing additional vocabulary along with a formal semantics."
SweetRules attempts to unite the most important kinds of rule and ontology languages using "a new, common knowledge representation (SCLP) in a new standardized syntax (RuleML), including the ability to cope with heterogeneity and resolve contradictory conflicts. It endeavors to capture most of the useful expressiveness, interoperably and scalably. It combines a large distributed set of rule and ontology knowledge bases that each are active, where each has a different associated engine for reasoning capabilities (inferencing, authoring, and/or translation ). Based upon recent fundamental KR theory advances, it includes semantics-preserving translations between different rule languages, systems, and families. Typical application areas include policies and authorizations; contracting, supply chain management; retailing, customer relationship management; business process automation and e-services; financial reporting and information."
SweetRules "supports the powerful Situated Courteous Logic Programs extension of RuleML, which includes prioritized conflict handling and procedural attachments for actions and tests. SweetRules' capabilities include first-of-a-kind semantics-preserving translation and interoperability between a variety of rule and ontology languages (including XSB Prolog, Jess production rules, HP Jena-2, IBM CommonRules, and the SWRL subset of RuleML), highly scaleable backward and forward inferencing, and easy merging of heterogeneous distributed rulebases/ontologies."
According to project leader Benjamin Grosof, SweetRules provides "not just one implementation, but a whole set of reference implementations for RuleML, which is the emerging standard for semantic business rules on the web. Indeed, it's really an entire platform for semantic web rules, focusing initially on interoperability and inferencing capabilities. The latest version for the first time puts the capability to do powerful RuleML-based application prototyping squarely in the hands of not only academic research developers, but also commercial advanced developers. Rule-based policies — for authorization, contracts, e-commerce, and mediation mapping — are a rich area of low hanging fruit for near-term applications based on this set of technologies."
Updating the Version V2.0 release of November 29, 2004, SweetRules Version V2.1 now provides support for web services. "WSDL Web Services are permitted as procedural attachments; initially, this is just for effecting not yet sensing. Rules can thus directly trigger WSDL Web Services as actions. An experimental extension of RuleML syntax is used to specify a WSDL web service; this supports dynamic creation/invocation of the WSDL Web Service client (via DII), and in Action Launcher, thus becomes available in SweetXSB, SweetJess, and SweetCR."
SweetRules development plans call for more comprehensive support of Web Services, including sensing and querying of Web Services; exposing functionality as Web Services through Web Services; importing knowledge bases and modules; support for events; support for Web Services protocols other than WSDL.
Version 2.1 also supports the user-friendly RuleML/SWSL presentation syntax. This presentation syntax is a concise ASCII syntax that is easier to use for editing than the XML syntax. This tool is the first ever to provide such support. Initially, this is just a generator not yet a parser. It involves an experimental extension of RuleML presentation syntax for Situated feature of LP (effector statements, sensor statements, attached procedures)."
SweetRules Version 2.1 also provides an open-source courteous compiler. A 'Courteous Compiler' "enables the courteous prioritized conflict handling expressive feature to be added to any LP rule system that supports negation-as-failure. The SweetRules 'first-ever in open source' reference implementation/algorithm for this technique removes the dependency on the IBM CommonRules Courteous Compiler.
SweetRules is a multi-institutional project "largely funded by the DAML (DARPA Agent Markup Language) program, which has pioneered US basic research in the area of the semantic web. The SweetRules team is collaborating closely with the RuleML Initiative, and is also collaborating with the Semantic Web Services Initiative and the Web Services Mediation Language effort. Led by Benjamin Grosof (Massachusetts Institute of Technology's Sloan School of Management), the SweetRules project team also includes researchers from University of Maryland Baltimore County, BBN Technologies, Stanford University, and University of Zurich, and has cooperation from researchers at IBM, HP, University of Karlsruhe, National Research Council of Canada and University of New Brunswick, State University of New York at Stonybrook, and Sandia National Labs."
From the SweetRules Version 2.1 Announcement
SweetRules, a uniquely powerful integrated set of tools for semantic web rules and ontologies, is newly enhanced in V2.1 with several first-of-a-kind capabilities, including support for rule-triggered WSDL Web Services, RuleML presentation syntax for user-friendlier editing, an open-source courteous compiler enabling prioritized conflict handling, and full non-stratified negation-as-failure via Jess production rules, along with a new installation wizard and additional examples of e-business application scenarios. The international SweetRules team today released V2.1 free on SemWebCentral, the semantic web community's largest repository for open source software tools, at http://sweetrules.semwebcentral.org.
Led by Benjamin Grosof, a professor of information technology at the Massachusetts Institute of Technology's Sloan School of Management, the SweetRules project team also includes researchers from University of Maryland Baltimore County, BBN Technologies, Stanford University, and University of Zurich, and has cooperation from researchers at IBM, HP, University of Karlsruhe, National Research Council of Canada and University of New Brunswick, State University of New York at Stonybrook, and Sandia National Labs.
SweetRules revolves around the RuleML emerging standard for semantic web rules, and supports the OWL standard for semantic web ontologies. RuleML and OWL use XML and, optionally, RDF. Available under the liberal LGPL open source license, SweetRules is the first platform for semantic web business rules.
SweetRules supports the powerful Situated Courteous Logic Programs extension of RuleML, which includes prioritized conflict handling and procedural attachments for actions and tests. SweetRules' capabilities include first-of-a-kind semantics-preserving translation and interoperability between a variety of rule and ontology languages (including XSB Prolog, Jess production rules, HP Jena-2, IBM CommonRules, and the SWRL subset of RuleML), highly scaleable backward and forward inferencing, and easy merging of heterogeneous distributed rulebases/ontologies.
Speaking on April 20  to an audience of 350
SweetRules' pluggability and composition capabilities enable new components to be added relatively quickly. Implemented in Java, SweetRules has a compact codebase: about 20,000 lines of code total for several dozen tools. This extensible kernel then enables effective interoperation among other rule (and ontology) systems whose combined code base totals an estimated several million lines. The openness of its source provides a blueprint for rule technology vendors and academics who wish to develop RuleML-based capabilities and interoperate their own systems with the other systems supported by SweetRules and RuleML.
"For many years, the semantic web community has focused heavily on the creation of ontologies that define the concepts and relationships within application areas. The SweetRules initiative is important because it provides an integrated framework with which developers can represent what an intelligent system actually should do with the static knowledge represented in ontologies. The use of rules is an important step toward the creation of intelligent web-based applications," said Mark Musen, head of Medical Informatics at Stanford University. Musen leads the Protégé semantic web knowledge-base editor toolkit project, and chairs the 2005 International Semantic Web Conference.
SweetRules' development has been largely funded by the DAML (DARPA Agent Markup Language) program, which has pioneered US basic research in the area of the semantic web. The SweetRules team is collaborating closely with the RuleML Initiative, and is also collaborating with the Semantic Web Services Initiative and the Web Services Mediation Language effort. Through these, it is cooperating with the World Wide Web Consortium, OASIS, and Object Management Group (OMG) standards bodies, as well.
V2.0, the first open source version, was released in Nov. 2004. Hundreds of users have already downloaded SweetRules, after its well-received demonstrations in detailed presentations this winter at the International Semantic Web Conference's tutorial program in Japan and at the DAML Principal Investigators Meeting in San Antonio, where it was highlighted by DARPA.
The major new technical features in V2.1, enhancing V2.0, include in particular:
WSDL Web Services are permitted as procedural attachments. Initially, this is just for effecting not yet sensing. Rules can thus directly trigger WSDL Web Services as actions. This is possibly a first-ever capability for any rigorously semantic rule system.
An installation wizard, with selective configuration, is provided. This reduces installation effort by 5-10X.
A new courteous compiler, the first ever in open source, is provided. This modular component enables the Courteous prioritized conflict handling expressive feature to be added to any rule system that supports negation-as-failure.
Full non-stratified NAF (negation-as-failure) is newly supported in SweetJess, the component that does translation and inferencing from RuleML into Jess production rules. This is a first-of-a-kind capability for any production rule system.
RuleML/SWSL presentation syntax support is newly provided. The presentation syntax is a concise ASCII syntax that is user-friendlier for editing than XML syntax. This tool is the first ever to provide such support. Initially, this is just a generator not yet a parser. In addition, V2.1 includes:
More application scenario examples, e.g., multi-agent e-commerce security/trust authorization and policy management (credit).
General polishing, including augmented documentation.
The lead developer for the V2.1 enhancement was Shashidhara Ganjugunte, a masters student at University of Maryland Baltimore County, who worked under the overall design supervision of Grosof. Ganjugunte was lead developer for the majority of the V2.0 code as well. Other SweetRules project core team members include Mike Dean, Said Tabet, Chitravanu Neogy, Sumit Bhansali, Timothy Finin, Anupam Joshi, and Dave Kolas. Additional team members include Mark Musen, Martin O'Connor, and Abraham Bernstein.
About the Rule Markup Initiative
Rules in (and for) the Web have become a mainstream topic since inference rules were marked up for E-Commerce and were identified as a Design Issue of the Semantic Web, and since transformation rules were put to practice for document generation from a central XML repository. Moreover, rules have continued to play an important role in AI shells for knowledge-based systems and in Intelligent Agents, today both needing a Web interchange format, and such XML/RDF-standardized rules are now also usable for the declarative specification of Web Services.
The Rule Markup Initiative has taken steps towards defining a shared Rule Markup Language (RuleML), permitting both forward (bottom-up) and backward (top-down) rules in XML for deduction, rewriting, and further inferential-transformational tasks...
The goal of the Rule Markup Initiative is to develop RuleML as the canonical Web language for rules using XML markup, formal semantics, and efficient implementations.
RuleML covers the entire rule spectrum, from derivation rules to transformation rules to reaction rules. RuleML can thus specify queries and inferences in Web ontologies, mappings between Web ontologies, and dynamic Web behaviors of workflows, services, and agents.
The Initiative develops a modular RuleML specification and transformations from and to other rule standards/systems. Moreover, it coordinates the development of tools to elicit, maintain, and execute RuleML rules. It also collects use cases, e.g. on business rules and reactive services..." [adapted from the RuleML home page]
RuleML Initiative and Web Services Modeling Ontology (WSMO) Working Group
An announcement of April 22, 2005, "RuleML and DERI Collaborate on Rules and Services Technologies Based on Their Standardization Initiatives":
RuleML, the leading provider of standards for rules technologies on the Web and in distributed platforms, and DERI (Digital Enterprise Research Institute), the leading European effort in Semantic Web Services that spearheads the Web Services Modeling Ontology (WSMO) working group, today announced the formation of a collaborative effort on integrating their platforms to enhance support for rules and services technologies. This collaboration explores the deployment and extension of the RuleML family of languages to integrate with the WSMO platform, focusing on rules and services interoperability on top of RuleML and WSML, WSMO's Language component. Anticipated benefits of this integration include that WSMO will take advantage of the modular flexibility and tools available in RuleML, and RuleML will be able to support the WSMO services modeling requirements.
RuleML is about rule interoperation between commercially important families of rule systems (including Production Rules, Relational and XML Databases, Event-Condition-Action Rules, Prolog, and others), as well as between industry standards relevant to rules — such as in the Semantic Web, XML, Web Services, Web Service Discovery, Web Service Composition, and Web Service Choreography, Business Processes, Privacy, Security, as well as Software Modeling and Interface Specifications.
WSMO describes various aspects of Semantic Web Services to decrease the need for human intervention for making heterogeneous components interoperable. It enables automatic Service discovery, composition, mediation and invocation. WSMO seeks to create a standard featuring simplicity (a solution to the integration problem that is as simple as possible), completeness (solves all aspects of the integration problem), and executability (a set of execution semantics exists as well as a reference implementation). It is being developed together with industrial as well as academic partners, and in alignment with various research projects..."
SemWebCentral is an Open Source development web site for the Semantic Web funded by the DARPA Agent Markup Language program. One purpose of SemWebCentral is to support the Semantic Web community by providing a free, centralized place for Open Source developers to manage Semantic Web software and content development. The other purpose is to provide resources for developers or other interested parties to learn about the Semantic Web and how to begin developing Semantic Web content and software.
SemWebCentral is intended for anyone interested in the Semantic Web. Current Semantic Web developers and Ontology designers will find the management and collaboration services available on this site valuable in developing their own projects as well as learning about and providing feedback to other Semantic Web projects. Those new to the Semantic Web will find the background resources and workflow wizard to be helpful in learning what the Semantic Web is and how they can begin using it..." [adapted from the About page]
W3C Workshop on Rule Languages for Interoperability
Workshop: 27-28 April 2005, Washington, D.C., USA.
"Rule languages and rule systems are widely used in applications ranging from database integration, service provisioning, and business process management to loan underwriting, privacy policies and Web services composition. General purpose rule languages remain relatively unstandardized, however, and rule systems from different suppliers are rarely interoperable.
Meanwhile, the Web has achieved remarkable success in allowing documents to be shared and linked throughout the world. More recently, Semantic Web languages like RDF and OWL are beginning to support data/knowledge sharing on the same scale and with considerable flexibility. Having a language for sharing rules is often seen as the next step in promoting data exchange on the Web.
This workshop, held by W3C with support from DARPA and hosted by ILOG, is intended to gather various participants and inputs needed to see how a standard rule framework might be developed, informed by Web Architecture and useful for addressing real user challenges...
Background to the Rule Languages Workshop
Rules are everywhere. They are found in many domains, disciplines, and industries. Business policies, laws and regulations, guidelines and best practices, definitions and axioms, database schema translations, workflow branching and technical constraints, all require a declarative and modular approach to their implementation. There is a thriving commercial market in several families of rule technologies, including production rules, event-condition-action rules, Prolog, relational database systems, and others. However, practical interoperability between these systems, especially across the different families, is currently quite limited.
Rules are a key element of the Semantic Web vision, allowing integration, derivation, and transformation of data from multiple sources in a distributed, transparent, and scalable manner. Rules can themselves be treated as data, published on the web, and when URIs (or QNames) are used as symbol-constants in a rule language, they can form useful links between knowledge bases. In a Web services environment, rules offer the opportunity to enable the automation of the enforcement and composition of policies governing the delivery of information, the access to services, or the execution of processes.
Rules have advantages of flexibility and manageability. In addition, the declarative nature of rules gives them a special appeal as a programmatic and knowledge representation device in a distributed and Web-based environment, where they can be owned, specified and managed in one place, and applied in many other places. This requires, however, a standard way to represent rules unambiguously for publication and interchange purposes. Different rules and a common foundation.
Rules come in a variety of forms for different uses and applications. Business rules, decision tables, and decision trees are used to automate the enforcement of business policies and regulations. Logical formulas, constraints, ontologies, association and transformation rules are used for inferencing in information retrieval and information integration, including databases, and metadata repositories (e.g., Dublin Core Initiative), or in analytical, forecasting and/or optimization applications.
Rules, however, trace their roots back to formal logic. There, semantics can be represented via a logical model theory and inference can be based on logical proof theory. The most important de facto semantic standard is first order predicate calculus, unchanged for nearly a hundred years. In the last three decades, declarative logic programs have emerged as a complement to first order logic, and provided the foundation for the semantics of relational databases and many rule languages. Algorithmic techniques and theory for formal logic have been extended to enable, and semantically treat: procedural attachments for built-ins, tests, and actions; and non-monotonicity for negation-as-failure, defaults, inheritance, prioritization, updating, revision, and conflict handling...
To be effective, practical, and deployable, a Web standard on rules needs to focus on the requirements of end users and the needs of rule technology providers. The goal of being able to transfer rulebases / knowledge bases, or simply to process them with different software, has helped motivate several important standardization or standards-proposing efforts including RuleML and SWRL, n3, Metalog, KIF and ISO Common Logic, ISO Prolog, and others. Some of those have been aimed at more or less specialized purposes, e.g., in the domains of Web Service policies (WS-Policy, WSPL, Policy RuleML, SWSL, WSML), access control and authorization (XACML, EPAL, P3P/APPEL), Business Rules (BRML, SRML), and other areas as well. Related standardization efforts have also started with respect to rule modeling (OMG's Business Semantics for Business Rules RFP and Production Rules Representation RFP) and rulebase execution (JSR 94 - Java API for Rules Engine)..." [from the Workshop Call for Participation]
- Announcement 2005-04-25: "First Platform for Semantic Web Rules Now Includes Web Services Support and More: SweetRules V2.1 Released Open Source."
- SweetRules Project web site
- Overview of SweetRules V2.1: Tools for Semantic Web Rules and Ontologies, including Translation, Inferencing, Analysis, and Authoring. Technical Overview. By Benjamin Grosof (MIT Sloan School of Management) and Mike Dean (BBN Technologies). April 24, 2005. 84 slides.
- SweetRules Discussion Forum
- SweetRules Rule Format Information Guide
- "RuleML and DERI Collaborate on Rules and Services Technologies Based on Their Standardization Initiatives." Announcement 2005-04. "This collaboration explores the deployment and extension of the RuleML family of languages to integrate with the WSMO platform, focusing on rules and services interoperability on top of RuleML and WSML, WSMO's Language component. Anticipated benefits of this integration include that WSMO will take advantage of the modular flexibility and tools available in RuleML, and RuleML will be able to support the WSMO services modeling requirements."
"Semantic Web Rules with Ontologies, and their E-Business Applications." By Benjamin Grosof and Mike Dean. Tutorial presented at the Third International Semantic Web Conference (ISWC-2004), Hiroshima, Japan, Nov. 7-11, 2004. "Rules are a main emerging area of the semantic web. There has been a large and exciting amount of recent progress in several aspects of semantic web rules, including: fundamental knowledge representation (KR) for rules; fundamental KR to integrate rules with ontologies; translations between heterogeneous commercial rule languages and systems/engines; development of algorithmic techniques and open-source tools for inferencing and interoperability/translations; standards proposals (including RuleML and SWRL); and pilot applications in e-business and other domains."
"Representing E-Commerce Rules Via Situated Courteous Logic Programs in RuleML." Draft version of article published in Electronic Commerce Research and Applications (ECRA) 3/1 (Spring 2004), pages 2-20. "We give an overview of current efforts to standardize e-business rules knowledge representation (KR) in XML as part of the Semantic Web. We focus especially on the design approach and criteria of RuleML, an emerging standard that we co-lead. We discuss the issues of standardization and Webizing which RuleML addresses. We extend, for the first time, RuleML's definition from the ordinary logic programs KR to situated courteous logic programs (SCLP), an expressively general KR that supports prioritized conflict handling and procedural attachments for actions and queries. We give an overview of our prototype SweetRules, (SemanticWEb Enabling Technology - Rules component), a set of tools which enable, for the first time, communication and inferencing of e-business rules represented in SCLP RuleML. We illustrate SCLP RuleML by giving example rulesets from the realm of e-commerce business policies in supply chain management."
"SweetDeal: Representing Agent Contracts With Exceptions Using Semantic Web Rules, Ontologies, and Process Descriptions." By Benjamin N. Grosof and Terrence C. Poon. In International Journal of Electronic Commerce (IJEC) 8/4 (Summer 2004), pages 61-98. "We address the problem in automated knowledge-based e-contracts of how to represent exception handling provisions — which in many (if not most) natural language contracts constitute the majority of the contract's volume. We make three main novel contributions. First, we newly extend the previous SweetDeal e-contracting approach to incorporate ontology knowledge, specifically ontologies about business processes, and show how that is useful to represent provisions for exception handling. We give a detailed application scenario of provisions about late delivery in manufacturing supply chain management (SCM). SweetDeal is a rule-based approach to representation of business contracts that enables software agents to create, evaluate, negotiate, and execute contracts with substantial automation and modularity. Its rules are represented in the Situated Courteous Logic Programs knowledge representation encoded in RuleML, the leading approach to Semantic Web rules. The process ontologies are represented in Description Logic encoded in DAML+OIL, the close predecessor of W3C's OWL, the leading approach to Semantic Web ontologies. Second, we give a new simple technical mechanism for the Semantic Web to integrate such rules on top of such ontologies. Rule predicates are defined by reference to classes or properties in ontology knowledge bases. This mechanism provides the basic technical approach to incorporate ontology knowledge into a SweetDeal e-contract. Third, we newly show how to represent, in DAML+OIL/OWL, process ontology knowledge drawn in particular from the MIT Process Handbook..."
"Rules in the Semantic Web Services Language (SWSL)." By Benjamin Grosof, Michael Kifer, and David L. Martin. W3C Workshop on Rule Languages for Interoperability. "The promise of Web services and the need for widely accepted standards enabling them are widely recognized, and considerable efforts are underway to define and evolve such standards in the commercial realm. Prominent among these are: OASIS's UDDI, BPEL4WS, and Web Services Security; and W3C's WSDL and Choreography Description Language. At the same time, recognition is growing of the need for richer semantic specifications of Web services, based on a comprehensive representational framework that spans the full range of service-related concepts. Because an expressive representation framework permits the specification of many different aspects of services, it can provide a foundation for a broad range of activities, across the Web service lifecycle, while enabling radically more and cheaper reuse of such specification knowledge across those aspects, across applications and organizations, and over the duration of the lifecycle. The Semantic Web Services Language (SWSL), and the associated First-order Ontology for Web Services (FLOWS), have been developed to meet this need. SWSL is a product of the Semantic Web Services Initiative (SWSI), a collaborative international research and early-phase standards effort..."
- SemWebCentral Home Page
- Contact: Benjamin Grosof, MIT Sloan School of Management, Information Technology Group. Web Technologies for E-Commerce, Business Policies, E-Contracting, Rules, XML, Agents, Semantic Web Services. WWW
- Earlier news:
- "W3C Announces Workshop on Rule Languages for Interoperability." News story 2005-02-21.
- "SWRL: A Semantic Web Rule Language Combining OWL and RuleML."
- "Workshop on Rule Markup Languages for Business Rules on the Semantic Web."
- "Korean Research Institute Develops the Extensible Rule Markup Language (XRML)."
- "Seminar on Rule Markup Techniques for the Semantic Web."
- "SRML Proposed as an XML Rule Representation for Java Rule Engines."
- W3C Workshop on Rule Languages 2005-04:
- References for (business) rule languages:
- Rule Markup Language (RuleML)
- Semantic Web Rule Language (SWRL)
- Semantic Web Rule Language First-Order Logic (SWRL FOL)
- Web Service Modeling Language (WSML)
- Business Rules Markup Language (BRML)
- "STARLab ORM Markup Language (ORM-ML)"
- "DARPA Agent Mark Up Language (DAML)"
- "Agent-Oriented Rule Markup Language (AORML)"
- "Extensible Rule Markup Language (XRML)"
- "Simple Rule Markup Language (SRML)
- XML Belief Network File Format (Bayesian Networks)
- Predictive Model Markup Language (PMML)
- Relational-Functional Markup Language (RFML)
- Ontology and Conceptual Knowledge Markup Languages
- Simple HTML Ontology Extensions (SHOE)
- XOL - XML-Based Ontology Exchange Language
- Description Logics Markup Language (DLML)
- Case Based Markup Language (CBML)
- Artificial Intelligence Markup Language (AIML)
- XML and Attribute Grammars