Agents, Multi-Agent Systems and Declarative Programming: Who, What, When, Where, Why, How?

This chapter tackles the relation between declarative languages and multi-agent systems by following the dictates of the five Ws (and one H) that characterize investigations. The aim is to present this research field, which has a long-term tradition, and discuss about its future. The first question to answer is "What? What are declarative agents and multi-agent systems?". Therefore, we will introduce the history of declarative agent systems up to the state of the art by answering the question "When? When did research on them begin?". We will, then, move to the question "Where? Where can it take place?": in which kind of real applications and for which kind of problems declarative agents and MAS have already proven useful? Connected to where is "Why? Why should it happen?". We will discuss the benefits of adopting the abstractions offered by declarative approaches for developing communication, interaction, cooperation mechanisms. We will compare with other technologies, mainly service-based and object-oriented ones. "Who? Who can be involved?": in order to exploit this kind of technology what sort of background does a specialist have to acquire? We address this question by looking at the Italian landscape of Computer Science research and education. Finally, with the question "How? How can it happen?" we will shortly report some examples of existing declarative languages and frameworks for the specification, verification, implementation and prototyping of agents and MAS.