FIPA Communicative Acts in Defeasible Logic

In agent communication languages, the inferences that
can be made on the basis of a communicative action are
inherently conditional, and non-monotonic. For exam-
ple, a proposal only leads to a commitment, on the con-
dition that it is accepted. And in a persuasion dialogue,
assertions may later be retracted. In this paper we there-
fore present a defeasible logic that can be used to express
a semantics for agent communication languages, and to
efficiently make inferences on the basis of communica-
tive actions. The logic is non-monotonic, allows nested
rules and mental attitudes as the content of communica-
tive actions, and has an explicit way of expressing per-
sistence over time. Moreover, it expresses that mental
attitudes are publicly attributed to agents playing roles
in the dialogue. To illustrate the usefulness of the logic,
we reformalize the meta-theory underlying the FIPA se-
mantics for agent communication, focusing on inform
and propose. We show how composed speech acts can
be formalized, and extend the semantics with an account
of persuasion