. The World Wide Web (WWW) can be viewed as the largest multimedia database that has ever existed. However, its support for query answering and automated inference is very limited. Metadata and domain specific ontologies were proposed by several authors to solve this problem. We developed Ontobroker which uses formal ontologies to extract, reason, and generate metadata in the WWW. The paper describes the formalisms and tools for formulating queries, defining ontologies, extracting metadata, and generating metadata in the format of the Resource Description Framework (RDF), as recently proposed by the World Wide Web Consortium (W3C). These methods provide a means for semantic based query handling even if the information is spread over several sources. Furthermore, the generation of RDF descriptions enables the exploitation of the ontological information in RDF-based applications.

In the field of Knowledge Engineering, dissatisfaction with the rapid-prototyping approach has led to a number of more principled methodologies for the construction of knowledgebased systems. Instead of immediately implementing the gathered and interpreted knowledge in a given implementation formalism according to the rapid-prototyping approach, many such methodologies centre around the notion of a conceptual model: an abstract, implementation independent description of the relevant problem solving expertise. A conceptual model should describe the task which is solved by the system and the knowledge which is required by it. Although such conceptual models have often been formulated in an informal way, recent years have seen the advent of formal and operational languages to describe such conceptual models more precisely, and operationally as a means for model evaluation. In this paper, we study a number of such formal and operational languages for specifying conceptual mode...

On2broker provides brokering services to improve access to heterogeneous, distributed and semistructured information sources as they are presented in the World Wide Web. It relies on the use of ontologies to make explicit the semantics of web pages. In the paper we will discuss the general architecture and main components of On2broker and provide some application scenarios. We show how we can provide semantic based access to web sources described with HTML, XML, or RDF.

. This paper provides an overview of the OCML modelling language: it illustrates the underlying philosophy, describes the main modelling constructs provided, and compares it to other modelling languages. 1. INTRODUCTION OCML 1 was originally developed in the context of the VITAL project (Shadbolt et al., 1993) to provide operational modelling capabilities for the VITAL workbench (Domingue et al., 1993). Over the years the language has undergone a number of changes and improvements and in what follows we will provide an overview of the current version of the language (v5.1), illustrate its underlying philosophy and compare it to other knowledge modelling languages. 2. LANGUAGE TENETS A number of ideas/principles have shaped the development of the OCML language. These are discussed in the following sections. 2.1. Knowledge-level modelling support. The main goal of OCML is to support knowledge-level modelling (Newell, 1982; Fensel and Van Harmelen, 1994). In practice this role impl...

Problem-solving methods provide reusable architectures and components for implementing the reasoning part of knowledge-based systems.

. The paper introduces an approach for the specification and verification of knowledge-based systems combining conceptual and formal techniques. We identify four elements of the specification of a knowledge-based system: a task definition, a problem-solving method, a domain model, and an adapter that relates the other elements. We present abstract data types and a variant of dynamic logic as formal means to specify and verify these different elements. As a consequence of our conceptual model we can decompose the overall verification task of the knowledge-based systems into different proof obligations. Each proof obligation deals with a different aspect of the entire system. The use of the conceptual model in specification and verification improves understandability and reduces the effort for both activities. The modularization enables reuse of specifications and proofs. A knowledge-based system can be build by combing and adapting different components. 1 INTRODUCTION During the last ...

One very successful approach to developing knowledge acquisition tools use expectations of what the user has to add or may want to add, based on how new knowledge fits within a knowledge base that already exists. When a knowledge base is first created or undergoes significant extensions and changes, these tools cannot provide much support. This paper presents an approach to creating expectations when a new knowledge base is built, and describes a knowledge acquisition tool that we implemented using this approach that supports users in creating problem-solving knowledge. As the knowledge base grows, the knowledge acquisition tool derives more frequent and more reliable expectations that result from enforcing constraints in the knowledge representation system, looking for missing pieces of knowledge in the knowledge base, and working out incrementally the inter-dependencies among the different components of the knowledge base. Our preliminary evaluations show a thirty percent time...

Ontologies now play an important role for many knowledge-intensive applications for which they provide a source of precisely defined terms. The terms are used for concise communication across people and applications. Tools such as ontology editors facilitate the creation and maintenance of ontologies. OntoEdit is an ontology editor that has been developed keeping five main objectives in mind: 1. Ease of use. 2. Methodology-guided development of ontologies. 3. Ontology development with help of inferencing. 4. Development of ontology axioms. 5.

This document is composed of three parts. The first part describes WebOnto, a tool providing web-based visualisation, browsing and editing support for developing and maintaining ontologies and knowledge models specified in OCML. The description is user-oriented, in the sense that it is meant to provide guidance to a user, rather than to describe the tool from a scholarly perspective. The second part of the document describes OCML, an operational knowledge modelling language, which provides the underlying representation for the ontologies and knowledge bases which can be developed using WebOnto. This second part is a revised version of chapter 4 of (Motta, 1999). The third part (Appendix 1), gives more details about the interpreters and reasoning facilities provided by OCML

. The paper introduces a formal approach for the specification and verification of knowledge-based systems. We identify different elements of such a specification: a task definition, a problem-solving method, a domain model, an adapter, and assumptions that relate these elements. We present abstract data types and a variant of dynamic logic as formal means to specify these different elements. Based on our framework we can distinguish several verification tasks. In the paper, we discuss the application of the Karlsruhe Interactive Verifier (KIV) for this purpose. KIV was originally developed for the verification of procedural programs but it fits well for our approach. We illustrate the verification process with KIV and show how KIV can be used as an exploration tool that helps to detect assumptions necessary to close the gap between the task definition and the competence of a problemsolving method. 1 Introduction During the last years, several conceptual and formal specification tech...