M.P. Singh - Agent Communication Languages: Rethinking the Principles

1. M.P. Singh - Agent Communication Languages: Rethinking the Principles Alessandro Giusti March, 28 2006

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

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

4. 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 FAILED FAILED

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

6. 1 - Perspective • Private • Sender’s perspective • Receiver’s perspective • Public • Multiagent system’s perspective Private perspectives are approximations of the public perspective

7. 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

8. 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

9. 2 - Type of meaning • Conventional meaning is needed • KQML and Arcol: personal meaning • Different communicative acts do not capture different conventions

10. 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)

11. 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

12. 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

13. 4 - Context Communication context: needed for understanding. • Fixed context • Flexible context Goal: flexible context

14. 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

15. 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)

16. 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

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

18. 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

19. 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

20. 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

21. 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

22. 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.