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Both OWL-DL and function-free Horn rules are decidable fragments of first-order logic with interesting, yet orthogonal expressive power. A combination of OWL-DL and rules is desirable for the Semantic Web; however, it might easily lead to the undecidability of interesting reasoning problems. Here, we present a decidable such combination where rules are(More)
The World Wide Web (WWW) can be viewed as the largest multime-dia database that has ever existed. However, its support for query answering and automated inference is very limited. Metadata and domain speciic ontologies were proposed by several authors to solve this problem. We developed Ontobroker which uses formal ontologies to extract, reason, and(More)
Technology for knowledge management has so far focused on the management of knowledge containers. We present an approach that is oriented towards managing knowledge contents instead by identifying knowledge items at various levels of formality. This is done by providing various types of meta data that are tied to ontologies for conceptual interlinkage.(More)
The World Wide Web (WWW) is currently one of the most important electronic information sources. However, its query interfaces and the provided reasoning services are rather limited. Ontobroker consists of a number of languages and tools that enhance query access and inference service of the WWW. The technique is based on the use of ontologies. Ontologies(More)
The customization of a natural language interface to a certain application, domain or knowledge base still represents a major effort for end users given the current state-of-the-art. In this article, we present our natural language interface ORA-KEL, describe its architecture, design choices and implementation. In particular, we present ORAKEL's adaptation(More)
Ontologies now play an important role for enabling the semantic web. They provide a source of precisely defined terms e.g. for knowledge-intensive applications. The terms are used for concise communication across people and applications. Typically the development of ontologies involves collaborative efforts of multiple persons. OntoEdit is an ontology(More)
Problem-solving methods provide reusable architectures and components for implementing the reasoning part of knowledge-based systems. The Unified Problem-solving Method description Language UPML has been developed to describe and implement such architectures and components to facilitate their semiautomatic reuse and adaptation. In a nutshell, UPML is a(More)
The vision of the Semantic Web can only be realized through proliferation of well-known ontologies describing different domains. To enable interoperability in the Semantic Web, it will be necessary to break these ontologies down into smaller, well-focused units that may be reused. Currently, three problems arise in that scenario. Firstly, it is difficult to(More)