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

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