We present a pragmatic extension of a Semantic Web query language (including so-called grounded conjunctive queries) with a termination safe functional expression language. This addresses problems encountered in daily usage of Semantic Web query languages for which currently no standardized solutions exist, e.g., how to define aggregation operators and used-defined filter predicates. We claim t...

Identifying data instances, that come from different sources but denote the same entity is necessary for effective integration of Semantic Web data. This “instance coreference” identification problem has gained attention in recent years. Although this is a critical aspect of the overall information integration problem in the Semantic Web, we put forward that information integration algorithms a...

The increasing number of infrastructure services requires the existence of mechanisms to discover and select services and resources, called service broker, based on customer requirements. This mechanism should improve the interoperability among customer-provider and be a backward compatible and light weight approach. The introduction of semantic annotations in service description (both function...

This paper is an extended version of one presented at ISWC 2004. In it, we present an abstract conceptual architecture for semantic web services. We define requirements on the architecture by analyzing a set of case studies developed as part of the EU Semantic Web-enabled Web Services project. The architecture is developed as a refinement and extension of the W3C Web Services Architecture. We a...

Web services are self-describing, self-contained applications that can be published, located, and invoked through common web protocols. Self-descriptions are in fact a form of metadata that provide details on the services offered. Semantic web services are, thus, an extension of such metadata-based descriptions to richer ontology-based description semantics. This paper provides an account on th...

Group centrality is an extension of the classical notion of centrality for individuals, to make it applicable to sets of them. We perform a SWOT (strengths, weaknesses, opportunities and threats) analysis of the use of group centrality in semantic networks, for different centrality notions: degree, closeness, betweenness, giving prominence to random walks. Among our main results stand out the r...

Today’s system programmers go to great lengths to extend the languages in which they program. For instance, system-specific compilers find errors in Linux and other systems, and add support for specialized control flow to Qt and event-based programs. These compilers are difficult to build and cannot always understand each other’s language changes. However, they can greatly improve code understa...

The paper presents a new semantic wiki architecture called PlWiki. The most important concept is to provide a strong knowledge representation and reasoning with Horn clauses-based representation. The idea is to use Prolog clauses on the lower level to represent facts and relations, as well as define rules on top of them. On the other hand a higher-level Semantic Web layer using RDF support is p...

Existing information retrieval systems provide users with limited support for efficient navigation in large semantically enriched information spaces. Several possible solutions were proposed, such as using faceted metadata search or semantic clusters of search results. We explore the possibilities of using enhanced faceted navigation with support for personalization, collaboration and Semantic ...