Catálogo de publicaciones - libros

This survey article introduces into the essential concepts and methods underlying rule-based query languages. It covers four complementary areas: declarative semantics based on adaptations of mathematical logic, operational semantics, complexity and expressive power, and optimisation of query evaluation.

The treatment of these areas is foundation-oriented, the foundations having resulted from over four decades of research in the logic programming and database communities on combinations of query languages and rules. These results have later formed the basis for conceiving, improving, and implementing several Web and Semantic Web technologies, in particular query languages such as XQuery or SPARQL for querying relational, XML, and RDF data, and rule languages like the “Rule Interchange Framework (RIF)” currently being developed in a working group of the W3C.

Coverage of the article is deliberately limited to declarative languages in a classical setting: issues such as query answering in F-Logic or in description logics, or the relationship of query answering to reactive rules and events, are not addressed.

This tutorial covers the very basics of Description Logics (DLs): first, we present the primary DL , namely its syntax, semantics, and reasoning problems, making use of a running example. Next, we discuss a few important extensions and explain DL’s relationship with first order logic, with modal logic, with OWL, and with rule-based formalisms, and give a brief sketch of tableau-based reasoning algorithms for DLs.

are used for programming rule-based, reactive systems, which have the ability to detect events and respond to them automatically in a timely manner. Such systems are needed on the Web for bridging the gap between the existing, passive Web, where data sources can only be accessed to obtain information, and the dynamic Web, where data sources are enriched with reactive behavior. This paper presents two possible approaches to programming rule-based, reactive systems. They are based on different kinds of reactive rules, namely and . Concrete reactive languages of both kinds are used to exemplify these programming paradigms. Finally the similarities and differences between these two paradigms are studied.

The Semantic Web aims at enabling sophisticated and autonomic machine to machine interactions without human intervention, by providing machines not only with data but also with its meaning (semantics). In this setting, traditional security mechanisms are not suitable anymore. For example, identity-based access control assumes that parties are known in advance. Then, a machine first determines the identity of the requester in order to either grant or deny access, depending on its associated information (e.g., by looking up its set of permissions). In the Semantic Web, any two strangers can interact with each other automatically and therefore this assumption does not hold. Hence, a semantically enriched process is required in order to regulate an automatic access to sensitive information. Policy-based access control provides sophisticated means in order to support protecting sensitive resources and information disclosure.

However, the term policy is often overloaded. A general definition might be “a statement that defines the behaviour of a system”. However, such a general definition encompasses different notions, including security policies, trust management policies, business rules and quality of service specifications, just to name a few. Researchers have mainly focussed on one or more of such notions separately but not on a comprehensive view. Policies are pervasive in web applications and play crucial roles in enhancing security, privacy, and service usability as well. Interoperability and self-describing semantics become key requirements and here is where Semantic Web comes into play. There has been extensive research on policies, also in the Semantic Web community, but there still exist some issues that prevent policy frameworks from being widely adopted by users and real world applications.

This document aims at providing an overall view of the state of the art (requirements for a policy framework, some existing policy frameworks languages, policy negotiation, context awareness, etc.) as well as open research issues in the area (policy understanding in a broad sense, integration of trust management, increase in system cooperation, user awareness, etc.) required to develop a successful Semantic Policy Framework.

Rules play an increasingly important role in a variety of Semantic Web applications as well as in traditional IT systems. As a universal medium for publishing information, the Web is envisioned to become the place for publishing, distributing, and exchanging rule-based knowledge. Realizing the importance and the promise of this vision, W3C has created the Rule Interchange Format Working Group (RIF WG) and chartered it to develop an interchange format for rules in alignment with the existing standards in the Semantic Web architecture stack.

However, creating a generally accepted interchange format is by no means a trivial task. First, there are different understandings of what a “rule” is. Researchers and practitioners distinguish between deduction rules, normative rules, production rules, reactive rules, etc. Second, even within the same category of rules, systems use different (often incompatible) semantics and syntaxes. Third, existing Semantic Web standards, such as RDF and OWL, show incompatibilities with many kinds of rule languages at a conceptual level.

This article discusses the role that different kinds of rule languages and systems play on the Web, illustrates the problems and opportunities in exchanging rules through a standardized format, and provides a snapshot of the current work of the W3C RIF WG.

Semantic wikis combine the collaborative environment of a classical wiki with features of semantic technologies. Semantic data is used to structure information in the wiki, to improve information access by intelligent search and navigation, and to enable knowledge exchange across applications. Though semantic wikis hardly support complex semantic knowledge and inferencing, we argue that this is not due to a lack of practical use cases. We discuss various tasks for which advanced reasoning is desirable, and identify open challenges for the development of inferencing tools and formalisms. Our goal is to outline concrete options for overcoming current problems, since we believe that many problems in semantic wikis are prototypical for other Semantic Web applications as well. Throughout the paper, we refer to our semantic wiki implementations and for practical illustration.

In the literature semantically enabled knowledge technologies are described as a new kind of web ([1], XI). In the science domain many ideas and interesting tool prototypes exist. In companies, however, there is less estimation for the effort and ways for using semantic web technologies. Special application scenarios for business purposes and experiences in real-life projects are necessary ([1], 303). This paper focuses on the need for semantic technologies from a business perspective and explains ideas of a scientific partner. Furthermore, the collaborative research project SoftWiki is introduced.

Today customers want to use powerful search engines for their huge and increasing content repositories. Full-text-only products with simple result lists are not enough to satisfy this community. Different content sources require different analyzing and indexing strategies and a content-specific result set presentation. There is a lot of research in the field of using semantic web technologies for information retrieval. A wide range of useful standard vocabularies and powerful frameworks have been developed that can be used to gather, transform and store metadata. However, in practise we see a gap between the state of art of information retrieval and customer needs with a defined prise-performance relation. It is a challenge to index a large file server with heterogeneous content annotated with metadata from different vocabularies, to provide an ontology-based navigation, to produce semantic annotated search results, to use faceted browsers as powerful filtering mechanism and do that with an out-of-the-box solution, which is stable, has a good performance and provides a simple way to configure it. With this viewpoint we present in this paper the usage of RDF-based semantic descriptions in an enterprise search solution developed at interface:projects.This paper covers lessons learned from developing a metadata-focused information retrieval system called . Especially we discuss the challenges and possible solutions in an enterprise (-wide) search scenario, and show the place where semantic descriptions matter in such a solution.

There are various B2B scenarios where many candidate services with the same or similar capability (provided by the same or even different service providers) can be used for enterprise application integration. Hence, a requester driving a B2B integration scenario can choose among several candidate services offering a capability satisfying its requests. However, the optimal choice of the service to be invoked often depends on the parameters of the request at run-time and preferences of the requester. This article describes an approach for a dynamic (at run-time) web service selection based on semantic interpretation of offered service capabilities and the parameters specifying the run-time request. The proposed solution takes into account special conditions on service usage either contractually agreed between requester and provider or specified by the requester without the knowledge of the provider. In general, those conditions restrict the interpretation of the original service capabilities as offered by a service provider (and discovered by the service requester) and influence the choice of a service. The approach is illustrated on an example from the shippercarrier domain.