M.P. Singh - Agent Communication Languages: Rethinking the Principles Alessandro Giusti March,

Agent Communication Languages Allow agents to communicate Interoperability (key feature) Other key agent features Autonomy Heterogeneity Sony Philips Microsoft

Reality check (1998) Verbatim: “Theoretically, an ACL should let heterogeneous agents communicate. However, none currently do.” No interoperability Who to blame? Philips Microsoft

Thesis Blame current ACLs Knowledge Query Management Language (KQML): based on wrong principles France Telecom’s Arcol: based on wrong principles FIPA ACL: based on wrong principles  A paradigm shift is needed

What principles? Analysis of communication dimensions: Perspective Type of meaning Semantic / Pragmatic focus Context Coverage of communicative acts

1 - Perspective Private Sender’s perspective Receiver’s perspective Public Multiagent system’s perspective Private perspectives are approximations of the public perspective

1 - Perspective Public perspective is needed: ACLs must be normative Agents must be tested for compliance The ACL must have a public perspective (or compliance testing is not possible) KQML and Arcol: private perspective

2 - Type of meaning Personal Meaning: intent or interpretation of receiver or sender Conventional Meaning: usage conventions Language is a system of conventions Different conventions need different communicative acts

2 - Type of meaning Conventional meaning is needed KQML and Arcol: personal meaning Different communicative acts do not capture different conventions

Dialects KQML failed because many dialects arose; Blame private perspective and personal meaning: Idiolects "When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean -- neither more nor less.“ Lewis Carroll, “Through the Looking-Glass, and What Alice Found There” (1871)

3 - Semantics versus pragmatics Meaning = Semantics + Pragmatics Semantics what symbols denote Pragmatics how syntactic symbols are interpreted and used involves mental states and the environment constrain how agents interact

3 - Semantics versus pragmatics Semantics-focused language is needed Pragmatics require fully-cooperative agents Pragmatics fail where sincerity cannot be taken for granted KQML and Arcol: Pragmatics-focused languages

4 - Context Communication context: needed for understanding. Fixed context Flexible context Goal: flexible context

5 - Coverage of communicative acts Seven categories: Assertives Directives Commissives Permissives Prohibitives Declaratives Expressives Limited coverage vs Full coverage Full coverage is needed KQML and Arcol have limited coverage

Opposing paradigms Mental Agency Focus on mental state (e.g. BDI) Assumes intentional stance How to determine the mental state of agents? Introspection: unsatisfactory or impossible “Mental state” is an abstract concept: only the agent designer warrants compliance. Social Agency Focus on agent behavior (external) “Social creatures” (sic) Compliance : obey conventions in society (self-evident)

Autonomy Design autonomy: agent designer’s freedom: Promotes heterogeneity and applications KQML and Arcol require that agents have BDI-based mental states Execution autonomy: agent’s freedom Arcol assumes sincere, cooperative, benevolent agents KQML is less strict

Proposed solution Social agency Different from traditional ACLs Goals: Public perspective Conventional meaning Semantics over pragmatics Flexible context Full communicative acts coverage

Protocols Agents play different roles Roles Define commitments/obligations Restrictions on behavior and communication Agents can manipulate/cancel commitments  Metacommitments (avoid chaos) Protocol Set of commitments Testability without introspection; closed-source friendly. Autonomy Everything is allowed as soon as commitments are met Context is society (“Social context”) Context is better known and agreed on  better communication

Dialects in societies Agent societies are free from idiolects No private perspective nor personal meaning Dialects  good Allow “context sensitivity” and real- world applications Do not involve introspection No risk of Humpty Dumptyism

Instantiation How is this translated into practice? No clear answer A purely behavior-based approach is not viable – too limiting. The purely-mentalist approach has been criticized so far Combine both solutions: Define when a communicative act is satisfied Assertive: if the world matches what is described Directive: the receiver acts to ensure success Commissive: the sender acts to ensure success Coarse canonical set of objective definitions Do not ascribe beliefs and intentions to agents

Comments / critique Rewrite: BDI-based languages have drawbacks: Too strict Require introspection for compliance testing Limits autonomy Requires full cooperation... but many of the critiques are not adequately justified. Behavior-Commitments based agencies sound good Upon closer inspection, they have their limits as well: not powerful enough. Proposed solution is a not-better defined mix between the two

Conclusion FIPA ACL is based on wrong principles... every possible communication dimension is wrong... but after 8 years FIPA ACL is the standard. Some of the proposed concepts are intriguing, but they can not be easily translated into practice.