About the Reasoning Web 2005 Proceedings

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This volume contains the tutorial papers of the Summer School “Reasoning Web,” July 25–29, 2005 (http://reasoningweb.org).

The School was hosted by the University of Malta and was organized by the Network of Excellence REWERSE “Reasoning on the Web with Rules and Semantics” (http://rewerse. net), funded by the EU Commission and by the Swiss Federal Office for Educa- tion and Science within the 6th Framework Programme under the project refer- ence number 506779. The objective of the school was to provide an introduction into methods and issues of the Semantic Web, a major endeavor in current Web research, where the World Wide Web Consortium W3C plays an important role.

The main idea of the Semantic Web is to enrich Web data with meta-data carrying a “meaning” of the data and allowing Web-based systems to reason about data (and meta-data). The meta-data used in Semantic Web applications is usually linked to a conceptualization of the application domain shared by different applications. Such a conceptualization is called an ontology and spec- ifies classes of objects and relations between them. Ontologies are defined by ontology languages, based on logic and supporting formal reasoning. Just as the current Web is inherently heterogeneous in data formats and data semantics, the Semantic Web will be inherently heterogeneous in its reasoning forms. In- deed, any single form of reasoning turns out to be insufficient in the Semantic Web. For instance, ontology reasoning in general relies on monotonic negation, while databases, Web databases, and Web-based information systems call for non-monotonic reasoning. Constraint reasoning is needed in dealing with time (for time intervals are to be dealt with). Reasoning with topologies, e.g., in mobile computing applications, requires planning methods. On the other hand (forward and/or backward) chaining is the reasoning of choice in coping with database-like views (for views, i.e., virtual data, can be derived from actual data by operations such as join and projections).

The programme of the school and the selection of the lecturers was discussed and approved by the REWERSE Steering Committee. This volume contains 10 papers written or co-authored by the lecturers. The papers present some well-established fundamentals of the Semantic Web and selected research issues addressed by REWERSE.

The first two papers concern the ontology level of the Semantic Web. The paper by Grigoris Antoniou, Enrico Franconi, and Frank van Harmelen gives an introduction to Semantic Web ontology languages and discusses their relation to description logics. An alternative foundation for Semantic Web reasoning is F-logic, as discussed in the paper by Michael Kifer.

The next two papers take the perspective of the Web as an information sys- tem. The first of them, co-authored by James Bailey, Fran ̧cois Bry, Tim Furche, and Sebastian Schaffert, surveys most Web and Semantic Web query languages so far proposed for the major representation formalisms of the standard and Semantic Web: XML, RDF and topic maps. The survey stresses the necessity of an integrated access to the data on the Web that is represented in various formalisms and discusses the role of reasoning in querying Web data. The size of this paper is larger than the other ones in this volume. This was necessary in order to provide a comprehensive and focused survey of numerous Web query languages. The second paper, by Jos ́e Ju ́lio Alferes and Wolfgang May, addresses the issue of evolution of Web data and reactivity to events. The paper first dis- cusses logical foundations of evolution and reactive languages in general and then focuses on issues specific to evolution and reactivity in the Web and in the Semantic Web.

User-friendliness of the Web is addressed by the next two papers. The first of them, by Matteo Baldoni, Cristina Baroglio, and Nicola Henze discusses the issue of personalization for the Semantic Web. Personalization techniques aim at giving the user optimal support in accessing, retrieving and storing information, where solutions are built so as to fit the preferences, the characteristics, and the taste of the individual. The objective of the paper is to provide a coherent in- troduction into issues and methods for realizing personalization in the Semantic Web. It shows that reasoning is essential for personalization. The paper by Nor- bert Fuchs, Stefan Ho ̈fler, Kaarel Kaljurand, Fabio Rinaldi, and Gerold Schnei- der gives a systematic introduction into Attempto Controlled English (ACE) a knowledge representation language readable by human and machine. ACE can be seen as a first-order logic language with the syntax of a non-ambiguous subset of English. It has already been used as an interface language to formal systems, and due to its ability to express business and policy rules it is of prime interest for Semantic Web applications.

The remaining papers in this volume show potentially important links be- tween the Semantic Web and some well-established techniques. The paper by Gerd Wagner addresses several issues of rule modeling on the basis of the Uni- fied Modeling Language (UML) proposed by the Object Management Group (OMG). It discusses similarities and differences between UML class models and vocabularies of the W3C ontology language OWL. It also shows how UML can be used for specifying rules and for providing concise descriptions of the abstract syntax of Semantic Web languages, such as RDF, OWL, and emerging Semantic Web rule languages. The paper by Robert Baumgartner, Thomas Eiter, Georg Gottlob, Marcus Herzog, and Christoph Koch surveys the state of the art and techniques in Web information extraction and explains their importance for cre- ation of input data for Semantic Web applications. The paper by Uwe Aßmann shows that employing ontologies can help to enlarge the software reuse factor and concludes that ontologies will play an important role in the construction of software applications, both singular and product lines. This concerns standard applications as well as Web applications, including Web services. Finally, the paper by Wlodzimierz Drabent argues that type checking is needed for Web rule and query languages. For that purpose the paper presents a formalism for de- scribing sets of semistructured data. Such sets, to be used as types, are related to XML schemata described in schema languages such as DTD or XML Schema. Research on their application to typechecking of REWERSE rule languages is in progress.

The aim of this chapter is to give a general introduction to some of the ontology languages that play a prominent role on the Semantic Web, and to discuss the formal foundations of these languages. Web ontology languages will be the main carriers of the information that we will want to share and integrate.

  • Rules and Ontologies in F-Logic

    F-logicisaformalismthatintegrateslogicwithobject-oriented programming in a clean and declarative fashion. It has been successfully used for information integration, ontology modeling, agent-based sys- tems, software engineering, and more. This paper gives a brief overview of F-logic and discusses its features from the point of view of an ontology language.

  • Web and Semantic Web Query Languages: A Survey

    A number of techniques have been developed to facilitate powerful data retrieval on the Web and Semantic Web. Three categories of Web query languages can be distinguished, according to the format of the data they can retrieve: XML, RDF and Topic Maps. This ar- ticle introduces the spectrum of languages falling into these categories and summarises their salient aspects. The languages are introduced us- ing common sample data and query types. Key aspects of the query languages considered are stressed in a conclusion.

  • Evolution and Reactivity for the Web

    The Web and the Semantic Web, as we see it, can be un- derstood as a “living organism” combining autonomously evolving data sources, each of them possibly reacting to events it perceives. Rather than a Web of data sources, we envisage a Web of Information Systems, where each such system, besides being capable of gathering information (querying persistent data, as well as “listening” to volatile data such as occurring events), is capable of updating persistent data, communicating the changes, requesting changes of persistent data in other systems, and being able to react to requests from other systems. The dynamic char- acter of such a Web requires declarative languages and mechanisms for specifying the evolution of the data.

    In this course we will talk about foundations of evolution and reactive languages in general, and will then concentrate on some specific issues posed by evolution and reactivity in the Web and in the Semantic Web.

  • Personalization for the Semantic Web

    Searching for the meaning of the word “personalization” on a popular search engine, one finds twenty-three different answers, includ- ing “the process of matching categorized content with different end users based on business rules … upon page request to a Webserver”, “using continually adjusted user profiles to match content or services to individ- uals”, and also “real-time tailoring of displays, particularly Web pages, to a specific customer’s known preferences, such as previous purchases”. A little more generally, personalization is a process by which it is pos- sible to give the user optimal support in accessing, retrieving, and stor- ing information, where solutions are built so as to fit the preferences, the characteristics and the taste of the individual. This result can be achieved only by exploiting machine-interpretable semantic information, e.g. about the possible resources, about the user him/herself, about the context, about the goal of the interaction. Personalization is realized by an inferencing process applied to the semantic information, which can be carried out in many different ways depending on the specific task. The objective of this paper is to provide a coherent introduction into issues and methods for realizing personalization in the Semantic Web.

  • Attempto Controlled English:A Knowledge Representation Language Readable by Humans and Machines

    Attempto Controlled English (ACE) is a knowledge repre- sentation language with an English syntax. Thus ACE can be used by anyone, even without being familiar with formal notations. The At- tempto Parsing Engine translates ACE texts into discourse represen- tation structures, a variant of first-order logic. Hence, ACE turns out to be a logic language equivalent to full first-order logic. The two views of ACE — natural language and logic language — complement each other, and render ACE both human- and machine-readable. This paper covers both views of ACE. In the first part we present the language ACE in a nutshell, and in the second part we give an overview of the discourse representation structures derived from ACE texts.

  • Rule Modeling and Markup

    In this paper we address several issues of rule modeling on the basis of UML. We discuss the relationship between UML class models and OWL vocabularies. We show how certain rules can be specified in a class diagram with the help of OCL. We also show how rule concepts can be described, and how the abstract syntax of RDF, OWL, SWRL and RuleML can be defined, by means of UML class diagrams in a concise way.

  • Information Extraction for the Semantic Web

    TheWorldWideWebrepresentsauniverseofknowledgeand information. Unfortunately, it is not straightforward to query and access the desired information. Languages and tools for accessing, extracting, transforming, and syndicating the desired information are required. The Web should be useful not merely for human consumption but additionally for machine communication. Therefore, powerful and user-friendly tools based on expressive languages for extracting and integrating information from various different Web sources, or in general, various heterogeneous sources are needed. The tutorial gives an introduction to Web technolo- gies required in this context, and presents various approaches and tech- niques used in information extraction and integration. Moreover, sample applications in various domains motivate the discussed topics and pro- viding data instances for the Semantic Web is illustrated1.

  • Reuse in Semantic Applications

    Applications using semantic technology are not fundamen- tally different from other software products. As standard applications, they need a well-defined development process, an appropriate modelling technology, and, to decrease construction cost, a good reuse technology for models and components. This paper shows that employing ontologies can help to enlarge the reuse factor. Ontologies improve the refinement process in object-oriented software development, simplify design of prod- uct lines, improve interoperability in component-based systems, and help in service-based applications, such as web services. Hence, ontologies will play an important role in the future engineering of software products.

Various schema languages have been introduced to describe (classes of) Web documents (DTD, XML Schema, Relax NG). We present mathematical treatment of their main features. We are interested in the sets of documents a schema defines; such sets will be called types. Using a mathematical formalism makes it possible to discuss chosen aspects of a schema language in a precise and simple way. Otherwise they are hidden among numerous details of a large and sophisticated schema language. Our goal is typing of rule languages, more precisely approximately de- scribing their semantics by means of types. Thus we are interested in formalisms for types that facilitate constructing (efficient) algorithms performing those operations on types that are needed in type checking and type inference for rules.

In the next article, we will discuss Reasoning Web 2006.

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