Abstract
The dilemma encountered in the design of an agent communication language (ACL) for an open society is that it should be based on externally observable phenomena yet it should capture something of the intuitions behind the high level abstractions typically found in internal mental states. Our solution treats an ACL message as a declarative statement that is given a procedural interpretation by a denotational semantics. This defines a speech act as a function between states. These states are social states which store public information including expressed mental attitudes and control variables. Expressed mental attitudes are externally observable and capture the conventional public meaning of communication. The variables control the flow of conversation in a protocol. We conclude firstly that since the denotational semantics is based on externally observable phenomena, it is possible to verify compliance and prove properties of protocols. Secondly, since the semantics is more expressive than behavioural specifications, it lays the foundation for high-level communication between intelligent agents.