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Web queries have been and will remain an essential tool for accessing, processing, and, ultimately, reasoning with data on the Web. With the vast data size on the Web and Semantic Web, reducing costs of data transfer and query evaluation for Web queries is crucial. To reduce costs, it is necessary to narrow the data candidates to query, simplify complex queries and reduce intermediate results. This article describes a static approach to optimization of web queries. We introduce a set of rules which achieves the desired optimization by schema and type based query rewriting. The approach consists in using schema information for removing incompleteness (as expressed by ‘descendant' constructs and disjunctions) from queries. The approach is presented on the query language Xcerpt, though applicable to other query languages like XQuery. The approach is an application of rules in many aspects—query rules are optimized using rewriting rules based on schema or type information specified in grammar rules. [ABSTRACT FROM AUTHOR]

Reactive Web systems, Web services, and Web-based publish/subscribe systems communicate events as XML messages, and in many cases require composite event detection: it is not sufficient to react to single event messages, but events have to be considered in relation to other events that are received over time. Emphasizing language design and formal semantics, we describe the rule-based query language XChangeEQ for detecting composite events. XChangeEQ is designed to completely cover and integrate the four complementary querying dimensions: event data, event composition, temporal relationships, and event accumulation. Semantics are provided as model and fixpoint theories; while this is an established approach for rule languages, it has not been applied for event queries before. [ABSTRACT FROM AUTHOR]

Reactivity, the ability to detect events and respond to them automatically through reactive programs, is a key requirement in many present-day information systems. Work on Web Services reflects the need for support of reactivity on a higher abstraction level than just message exchange by HTTP. This article presents the composite event query facilities of the reactive rule-based programming language XChange. Composite events are important in the dynamic world of the Web where applications, or Web Services, that have not been engineered together are composed and have to cooperate by exchanging event messages. [ABSTRACT FROM AUTHOR]

GALEN seeks to provide re-usable terminology resources for clinical systems. The heart of GALEN is the Common Reference Model (CRM) formulated in a specialised description logic. The CRM is based on a set of principles that have evolved over the period of the project and illustrate key issues to be addressed by any large medical ontology. The principles on which the CRM is based are discussed followed by a more detailed look at the actual mechanisms employed. Finally the structure is compared with other biomedical ontologies in use or proposed. [ABSTRACT FROM AUTHOR]

The life sciences are a promising application area for semantic web technologies as there are large online structured and unstructured data repositories and ontologies, which structure this knowledge. We briefly give an overview over biomedical ontologies and show how they can help to locate, retrieve, and integrate biomedical data. Annotating literature with ontology terms is an important problem to support such ontology-based searches. We review the steps involved in this text mining task and introduce the ontology-based search engine GoPubMed. As the underlying data sources evolve, so do the ontologies. We give a brief overview over different approaches supporting the semi-automatic evolution of ontologies. [ABSTRACT FROM AUTHOR]

Semantic Web technology is being increasingly applied in a large spectrum of applications in which domain knowledge is conceptualized and formalized (e.g., by means of an ontology) in order to support diversified and automated knowledge processing (e.g., reasoning) performed by a machine. Moreover, through an optimal combination of (cognitive) human reasoning and (automated) machine reasoning and processing, it is possible for humans and machines to share complementary tasks. The spectrum of applications is extremely large and to name a few: corporate portals and knowledge manage-ment, e-commerce, e-work, e-business, healthcare, e-government, natural language understanding and automated translation, information search, data and services integration, social networks and collaborative filtering, knowledge mining, business intelligence and so on. From a social and economic perspective, this emerging technology should contribute to growth in economic wealth, but it must also show clear cut value for everyday activities through technological transparency and efficiency. The penetration of Semantic Web technology in industry and in services is progressing slowly but accelerating as new success stories are reported. In this paper and lecture we present ongoing work in the cross-fertilization between industry and academia. In particular, we present a collection of application fields and use cases from enterprises which are interested in the promises of Semantic Web technology. The use cases are detailed and focused on the key knowledge processing components that will unlock the deployment of the technology in the selected application field. The paper ends with the presentation of the current technology roadmap designed by a team of Academic and Industry researchers. [ABSTRACT FROM AUTHOR]

To master large rule sets in ontologies and other logic-based specifications, the ability to divide them into components plays an important role. While a naive approach treats the rule sets as black-box components and composes them via combinators, their relationships are usually so complicated that this approach fails to be useful in many scenarios. Instead, the components should be "opened" before composition. The paper presents several such "gray-box composition" techniques, namely fragment-based genericity and extension, inline template expansions, semantic macros, and mixin layers. All approaches help to structure large ontologies and rule-based specifications into fine-grained components, from which they can be built up flexibly. [ABSTRACT FROM AUTHOR]

In this paper we address computational aspects of protein structure and function, including prediction of secondary structure, folding, structure determination from Nuclear Magnetic Resonance data, modelling of protein interactions, and metabolic pathways. The subject is introduced with an overview of protein structure and chemistry and the algorithms and representations used to model protein structures. The main focus of the paper is the integration of information from sources relevant to protein structure modelling, such as structure databases and modelling servers, a task made difficult by the heterogeneity of formats, the diversity of data sources, and the sheer volume of information available, making evident the need for a standard framework for data sharing, i.e. the Semantic Web. To help solve this problem, we present tools being developed according to the concept of a Semantic Web. These include the UniProtRDF project and tools currently implemented on the Chemera molecular modelling software which can facilitate the search and application of information available from Internet servers and databases. [ABSTRACT FROM AUTHOR]

This article is firstly an introduction into query languages for the Semantic Web, secondly an in-depth comparison of the languages introduced. Only RDF query languages are considered because, as of the writing of this paper, query languages for other Semantic Web data modeling formalisms, especially OWL, are still an open research issue, and only a very small number of, furthermore incomplete, proposals for querying Semantic Web data modeled after other formalisms than RDF exist. The limitation to a few RDF query languages is motivated both by the objective of an in-depth comparison of the languages addressed and by space limitations. During the three years before the writing of this article, more than three dozen proposals for RDF query languages have been published! Not only such a large number, but also the often immature nature of the proposals makes the focus on few, but representative languages a necessary condition for a non-trivial comparison. For this article, the following RDF query languages have been, admittedly subjectively, selected: Firstly, the "relational" or "pattern-based" query languages SPARQL, RQL, TRIPLE, and Xcerpt; secondly the reactive rule query language Algae; thirdly and last the "navigational access" query language Versa. Although subjective, this choice is arguably a good coverage of the diverse language paradigms considered for querying RDF data. It is the authors' hope and expectation, that this comparison will motivate and trigger further similar studies, thus completing the present article and overcoming its limitation. [ABSTRACT FROM AUTHOR]

The semantic web community and the business rules community have common roots. This article explores the differences and similarities between the two fields in order to encourage collaboration between the communities with respect to standardization efforts and research topics. Keywords: Business rules, Semantic Web, SBVR, Rule standards, Reasoning languages, Specification languages. [ABSTRACT FROM AUTHOR]

We present some recent results on the definition of logic-based systems integrating ontologies and rules. In particular, we take into account ontologies expressed in Description Logics and rules expressed in Datalog (and its nonmonotonic extensions). We first introduce the main issues that arise in the integration of ontologies and rules. In particular, we focus on the following aspects: (i) from the semantic viewpoint, ontologies are based on open-world semantics, while rules are typically interpreted under closed-world semantics. This semantic discrepancy constitutes an important obstacle for the definition of a meaningful combination of ontologies and rules; (ii) from the reasoning viewpoint, the interaction between an ontology and a rule component is very hard to handle, and does not preserve decidability and computational properties: e.g., starting from an ontology in which reasoning is decidable and a rule base in which reasoning is decidable, reasoning in the formal system obtained by integrating the two components may not be a decidable problem. Then, we briefly survey the main approaches for the integration of ontologies and rules, with special emphasis on how they deal with the above mentioned issues, and present in detail one of such approaches, i.e., ${{\cal DL}\textit{+log}}$. Finally, we illustrate the main open problems in this research area, pointing out what still prevents us from the development of both effective and expressive systems able to integrate ontologies and rules. [ABSTRACT FROM AUTHOR]

For realizing the Semantic Web vision, extensive work is underway for getting the layers of its conceived architecture ready. Given that the Ontology Layer has reached a certain level of maturity with W3C recommendations such as RDF and the OWL Web Ontology Language, current interest focuses on the Rules Layer and its integration with the Ontology Layer. Several proposals have been made for solving this problem, which does not have a straightforward solution due to various obstacles. One of them is the fact that evaluation principles like the closed-world assumption, which is common in rule languages, are usually not adopted in ontologies. Furthermore, naively adding rules to ontologies raises undecidability issues. In this paper, after giving a brief overview about the current state of the Semantic-Web stack and its components, we will discuss nonmonotonic logic programs under the answer-set semantics as a possible formalism of choice for realizing the Rules Layer. We will briefly discuss open issues in combining rules and ontologies, and survey some existing proposals to facilitate reasoning with rules and ontologies. We will then focus on description-logic programs (or dl-programs, for short), which realize a transparent integration of rules and ontologies supported by existing reasoning engines, based on the answer-set semantics. We will further discuss a generalization of dl-programs, viz.hex-programs, which offer access to different ontologies as well as higher-order language constructs. [ABSTRACT FROM AUTHOR]

Consider the following two conceptions of the Semantic Web: - A web of (logic based) knowledge representations. - A web of (semi-)structured data. In both conceptions, the common factor (the web) imposes certain requirements: extremely variable scalability (from a home page to community sites to sites that encompass a significant fraction of the web), rapid evolution, radical distribution, arbitrary interconnection and aggregation, and very little validation or other means of control. The demands of the web are forcing both the knowledge representation (KR) and the database communities to stretch their understanding and technology in different ways. [ABSTRACT FROM AUTHOR]

Event-Condition-Action (ECA) rules offer a flexible, adaptive, and modular approach to realizing business processes. This article discusses the use of ECA rules for describing business processes in an executable manner. It investigates the benefits one hopes to derive from using ECA rules and presents the challenges in realizing business processes. These constitute a list of requirements for an (executable) business process description language, and we take them as a basis to investigate suitability of the concrete ECA rule language XChange in realizing a business process from the EU-Rent Case Study. [ABSTRACT FROM AUTHOR]

Styling and formatting of XML documents for various target media is often specified with the Cascading Style Sheet (CSS) language. An appealing feature of CSS is that it specifies formatting instructions using rather simple guarded rules. A limitation of CSS is that it focuses on static formatting rules. As a consequence scripting languages such as ECMA Script are used in practice for dynamic adaptation of formatting. CSSNG is a novel extension of CSS 3, the newest version of CSS, introducing just a few rules for a dynamic rendering and for markup visualization. This limited extension of CSS 3 turns out to make possible a rather advanced visualization of programs. This article (1) introduces into the extensions of CSSNG with respect to CSS 3, (2) describes a proof-of-concept prototype implementation of CSSNG, and (3) demonstrates CSSNG on Xcerpt query programs. [ABSTRACT FROM AUTHOR]

This article describes the advantages of the computer query language Xcerpt to find and access web data. Although there are several other languages, the authors contend Xcerpt is the best due to its versatility and its ability to access many web formats. They demonstrate Xcerpt's pattern matching constructs and its superior implementation.

Web query languages promise convenient and efficient access to Web data such as XML, RDF, or Topic Maps. Xcerpt is one such Web query language with strong emphasis on novel high-level constructs for effective and convenient query authoring, particularly tailored to versatile access to data in different Web formats such as XML or RDF. However, so far it lacks an efficient implementation to supplement the convenient language features. AMaχoS is an abstract machine implementation for Xcerpt that aims at efficiency and ease of deployment. It strictly separates compilation and execution of queries: Queries are compiled once to abstract machine code that consists in (1) a code segment with instructions for evaluating each rule and (2) a hint segment that provides the abstract machine with optimization hints derived by the query compilation. This article summarizes the motivation and principles behind AMaχoS and discusses how its current architecture realizes these principles. [ABSTRACT FROM AUTHOR]

As the Semantic Web is gaining momentum, the need for truly versatile query languages becomes increasingly apparent. A Web query language is called versatile if it can access in the same query program data in different formats (e.g. XML and RDF). Most query languages are not versatile: they have not been specifically designed to cope with both worlds, providing a uniform language and common constructs to query and transform data in various formats. Moreover, most mainstream query languages do not provide a flexible data model that is powerful enough to naturally convey both Semantic Web data formats (especially RDF and Topic Maps) and XML. This article highlights challenges related to the data model and language constructs for querying both standard Web and Semantic Web data with an emphasis on facilitating sophisticated reasoning. It is shown that Xcerpt's data model and querying constructs are particularly well-suited for the Semantic Web, but that some adjustments of the Xcerpt syntax allow for even more effective and natural querying of RDF. [ABSTRACT FROM AUTHOR]

Reactivity, the ability to detect and react to events, is an essential functionality in many information systems. In particular, Web systems such as online marketplaces, adaptive (e.g., recommender) systems, and Web services, react to events such as Web page updates or data posted to a server. This article investigates issues of relevance in designing high-level programming languages dedicated to reactivity on the Web. It presents twelve theses on features desirable for a language of reactive rules tuned to programming Web and Semantic Web applications. [ABSTRACT FROM AUTHOR]

The Semantic Web is an endeavour aiming at enhancing Web data with meta-data and data processing, as well as processing methods specifying the "meaning" of such data and allowing Web-based systems to take advantage of "intelligent" reasoning capabilities. The representation of the meaning of data essentially requires the development of a world model. Ontologies, for example, are logical descriptions of world models. In this paper we investigate what it means to develop a world model for "geospatial" data that can be used for Semantic Web applications. Different aspects are analysed and a proposal for a concrete architecture is developed. The architecture takes into account that geospatial data (road maps etc.) are usually owned by companies and only accessible through their interfaces. The article also argues that, to complement standard, general purpose, logic-based data modelling and reasoning methods, as e.g. offered by RDF and OWL and reasoners for these languages, location reasoning is best tackled using graphs for data modelling and well-established algorithms for reasoning. Hence, the article illustrates, for the practical case of location reasoning for providing guidance, the thesis that, on the Semantic Web, "theory reasoning" is a desirable complement to "standard reasoning". [ABSTRACT FROM AUTHOR]

Metadata processing is recognized as a central challenge for database research in the next decade. Already, novel desktop data management and search applications (cf. Apple's Spotlight and Microsoft's WinFS) are enabled by rich metadata. Efficient and effective access to such data becomes a crucial issue for more and more application scenarios. In this article, we focus on metadata represented in RDF. A number of query languages for RDF have been presented in recent years. This article argues that most of these approaches fail to address properly two core issues: the provision of rich operators and constructs to adequately support RDF's graph data model and the ability to intertwine access to metadata (in RDF format) and data (in XML format). To address this points, two XML views over RDF data are expressed in the query language Xcerpt and discussed. Furthermore, it is shown how these views together with Xcerpt's rich graph patterns allow the succinct expression of complex, but common queries against RDF graphs. [ABSTRACT FROM AUTHOR]

This articles discusses the logic, or logic-based, languages required for a full deployment of the Semantic Web. It presents ten theses addressing 1the kinds of logic languages needed, 2data and data processing, 3semantics, and 4engineering and rendering issues. The views reported about in this article have been presented at the W3C Workshop on Rule Languages for Interoperability 27-28 April 2005, Washington, D.C., USA, http://www.w3.org/2004/12/rules-ws/. [ABSTRACT FROM AUTHOR]

This article introduces a programming language approach to modelling spatio-temporal data using calendars and topologies specified as types. Calendric and topologic data appearing in Web applications are most often rather complex, sometimes involving different calendars and/or topologies. The basic principle is to model spatio-temporal data by means of predicate subtyping. This principle is used to define calendric and topologic data types representing granularities as well as conversions between those data types. A thesis underlying this work is that calendars and topologies are more conveniently expressed with dedicated language constructs and that calendar and topology data are more efficiently processed with dedicated reasoning methods than with general purpose "axiomatic reasoning" of e.g. ontology languages or theorem provers. [ABSTRACT FROM AUTHOR]

This article introduces XChange, a rule-based reactive language for the (Semantic) Web. Stressing application scenarios, it first argues that high-level reactive languages are needed for both Web and Semantic Web applications. Then, it discusses technologies and paradigms relevant to high-level reactive languages for the (Semantic) Web. [ABSTRACT FROM AUTHOR]

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 article introduces the spectrum of languages falling into these categories and summarises their salient aspects. The languages are introduced using common sample data and query types. Key aspects of the query languages considered are stressed in a conclusion. [ABSTRACT FROM AUTHOR]