Abstract
This paper discusses an approach to adding explicit ontologies in multi-agent systems based on logic programming. Ontologies are content theories about knowledge domains, developed to clarify knowledge structure and enhancing knowledge reuse and standardization. Ontologies allow explicit organization of knowledge in agent-based applications, and unambiguous description of characteristics and properties of agents. We consider in detail the use of explicit ontologies in CaseLP, a declarative logical framework for prototyping agent-based applications. Our running example comes from the domain of sport results, to which CaseLP has been applied. Concepts such as sport, competition, competitors are included in the ontology, as well as relationships that relate these concepts. We introduce an agent level ontology to formalize attributes and functionalities of CaseLP agents, for example their kind, architecture and services, either at the domain level or at the agent level. Domain and agent level ontologies are exploited in CaseLP to perform semantic checks of agent architectural descriptions, to check agent behavioural rules used by an agent to provide its services, and as a knowledge repository to be exploited during agent execution.