What are Ontologies Useful For?

This chapter is a reasoned survey about the main roles of ontologies in the Web era. It starts by providing a background enabling the reader to understand what ontologies in Computer Science are. Then it shows the most meaningful uses of ontologies and discuss the role of inferences and reasoners about ontological knowledge. Once the decision to use semantic knowledge has been taken, next step is to find or build the suited ontology. To this purpose, the chapter shows how existing ontologies can be found and reused. Moreover, it presents some methodologies for building ontologies and some tools supporting ontology development. The last section highlights open issues related to reasoning mechanisms, ontology mapping, ontology evolution, and automatic ontology development. The main goal of this chapter is to provide the reader with a synthesis of the advantages and limitations that the usage of ontologies has in Computer Science, in order to enable her/him to take informed decisions concerning the exploitation of ontological knowledge within different kinds of projects.