The World Wide Web (WWW) is a global, ubiquitous, and fundamentally dynamic environment for information exchange and processing. By connecting vast numbers of individuals, the Web enables creation of virtual communities, and during the last 10 years, became a universal collaboration infrastructure. The so-called Semantic Web, a concept proposed by Tim Berners-Lee, is a new WWW architecture that enhances content with formal semantics (Berners-Lee, Hendler, & Lassila, 2001). Hence, the Web content is made suitable for machine processing (i.e., it is described by the associated metadata), as opposed to HTML documents available only for human consumption. Languages such as Resource Description Framework (RDF) and Ontology Web Language (OWL) along with well-known XML are used for description of Web resources. In other words, the Semantic Web is a vision of the future Web in which information is given explicit meaning. This will enable autonomous software agents to reason about Web content and produce intelligent responses to events (Staab, 2002). The ultimate goal of the next generation’s Web is to support the creation of virtual communities which will be composed of software agents and humans cooperating within the same environment. Sharing knowledge within such a community requires a shared conceptual vocabularies—ontologies, which represent the formal common agreement about the meaning of data (Gomez-Perez & Corcho, 2002). Artificial intelligence defines ontologies as explicit, formal specification of a shared conceptualization (Studer, Benjamins, & Fensel, 1998). In this case, a conceptualization stands for an abstract model of some concept from the real world; explicit means that the type of concept used is explicitly defined. Formal refers to the fact that an ontology should be machine readable; and finally shared means that ontology expresses knowledge that is accepted by all the subjects. In short, an ontology defines the terms used to describe and represent an area of knowledge. However, the shared ontologies must be first constructed by using information from many sources which may be of arbitrary quality. Thus, it is necessary to find a way to seamlessly combine the knowledge from many sources, maybe diverse and heterogeneous. The resultant ontologies enable virtual communities and teams to manage and exchange their knowledge. It should be noted, that the word ontology has been used to describe notions with different degrees of structure—from taxonomies (e.g., Yahoo hierarchy), metadata schemes (e.g., Dublin Core), to logical theories. The Semantic Web needs ontologies with a significant degree of structure. These should allow the specification of at least the following kinds of things: • Concepts (which identify the classes of things like cars or birds) from many domains of interest • The relationships that can exist among concepts • The properties (or attributes) those concepts may have
