Conjunctive queries play an important role as an expressive query language for Description Logics (DLs). Although modern DLs usually provide for transitive roles, it was an open problem whether conjunctive query answering over DL knowledge bases is decidable if transitive roles are admitted in the query. In this paper, we consider conjunctive queries over knowledge bases formulated in the popular DL SHIQ and allow transitive roles in both the query and the knowledge base. We show that query answering is decidable and establish the following complexity bounds: regarding combined complexity, we devise a deterministic algorithm for query answering that needs time single exponential in the size of the KB and double exponential in the size of the query. Regarding data complexity, we prove co-NP-completeness. 1

Abstract. A web of linked RDF data may be enabled by standards specifying how links should be made in RDF and under what conditions they should be followed as well as powerful generic RDF browsers that can traverse an open web of RDF resources. The Tabulator is an RDF browser, which is designed both for new users to provoke interest in the Semantic Web and give them a means to access and interact with the entire web of RDF data, and for developers of RDF content to provide incentive for them to post their data in RDF, to refine and promote RDF linking standards, and to let providers see how their data interacts with the rest of the Semantic Web. A challenge for Semantic Web browsers is to bring the power of domain-specific applications to a generic program when new unexpected domains can be encountered in real time. The Tabulator project is an attempt to demonstrate and utilize the power of linked RDF data with a user-friendly Semantic Web browser that is able to recognize and follow RDF links to other RDF resources based on the user’s exploration and analysis. 1

Abstract. We describe the instance store, a system for reasoning about individuals (i.e., instances of classes) in OWL ontologies. By using a hybrid reasoner/database architecture, our system is able to perform efficient reasoning over large volumes of instance data, as required by many real world applications. 1

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We present extended conceptual logic programs (ECLPs), for which reasoning is decidable and, moreover, can be reduced to finite answer set programming.

We extend Answer Set Programming with, possibly infinite, open domains.

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Today, many applications require users from one organization to access data belonging to organizations. While traditional solutions offered for the federated and mediated databases facilitate this by sharing metadata, this may not be acceptable for certain organizations due to privacy concerns. In this paper, we propose a novel solution – Privacy-preserving Access Control Toolkit (PACT) – that enables privacy-preserving secure semantic access control and allows sharing of data among heterogeneous databases without having to share metadata. PACT uses encrypted ontologies, encrypted ontology-mapping tables and conversion functions, encrypted role hierarchies and encrypted queries. The encrypted results of queries are sent directly from the responding system to the requesting system, bypassing the mediator to further improve the security of the system. PACT provides semantic access control using ontologies and semantically expanded authorization tables at the mediator. One of the distinguishing features of the PACT is that it requires very little changes to underlying databases. Despite using encrypted queries and encrypted mediation, we demonstrate that PACT provides acceptable performance.

Abstract. The use of Web services as a means of dynamically discovering, negotiating, composing, executing and managing services to materialize enterprise-scale workflow is an active research topic. Existing approaches involve many disparate concepts, frameworks and technologies. What is needed is a comprehensive and overarching framework that handles the processing and workflow requirements of Virtual Organizations, maps them to a collection of service-oriented tasks, dynamically configures these tasks from available services, and manages the choreography and execution of these services. The goal is to add semantics to Web services to endow them with capabilities needed for their successful deployment in enterprise-scale systems for Virtual Organizations. This paper introduces such a framework, the Knowledge-based Dynamic Semantic Web Services (KDSWS) Framework that addresses in an integrated end-to-end manner, the life-cycle of activities involved in preparing, publishing, requesting, discovering, selecting, configuring, deploying, and delivering Semantic Web Services. In particular, the following issues are addressed with an emphasis on adaptability to rapidly changing environments and standards: 1) semantic specification of both service’s and requestor’s capabilities, constraints and preferences including quality of service, trust, and security; 2) transaction control and workflow management; and 3) resource management, interoperation and evolution of the Virtual Organization.

Summary. Modularity of ontologies is currently an active research field, and many different notions of a module have been proposed. In this paper, we review the fundamental principles of modularity and identify formal properties that a robust notion of modularity should satisfy. We explore these properties in detail in the contexts of description logic and classical predicate logic and put them into the perspective of well-known concepts from logic and modular software specification such as interpolation, forgetting and uniform interpolation. We also discuss reasoning problems related to modularity. 1