m.p. singh - agent communication languages: rethinking the principles alessandro giusti march, 28...
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M.P. Singh - Agent Communication Languages: Rethinking the Principles
Alessandro Giusti
March, 28 2006
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.