PLACA

Thomas’s PLAnning Communicating Agents language: an extension of Shoham’s Agent-Oriented Programming with first-class planning constructs, so that agents can both commit to and reason about future courses of action in their communications.

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Summary

Shoham introduces Agent-Oriented Programming (AOP) as a specialization of object-oriented programming in which the state of each module — now called an agent — is a mental state composed of beliefs, capabilities, decisions/choices, commitments, and obligations. Interpretation of these components is formally grounded in an extension of standard epistemic logics that adds temporality, obligation, decision, and capability operators.

Agents communicate via speech-act-inspired primitives (inform, request, offer, promise, decline, etc.), constrained by rules such as honesty and consistency. The paper defines a class of agent interpreters and presents AGENT-0, a concrete implemented language whose semantics is tied to the mental-state logic. Shoham also discusses “agentification” — converting arbitrary devices into AOP-programmable agents — and situates AOP against BDI architectures, speech act theory, and McCarthy’s Elephant2000.

Conceptual Contribution

Claim: Programming can be fruitfully specialised to an “agent” paradigm in which module state is a formally specified mental state and inter-module communication is a speech act constrained by rational/ethical rules.

Mechanism: Shoham extends standard modal-epistemic logic with temporal, obligation, decision and capability operators, defines the mental-state components of an agent (belief, capability, commitment, choice, obligation), then specifies a generic agent interpreter cycle (update mental state, execute commitments, handle incoming messages) and instantiates it in AGENT-0, whose programs are condition-action rules over mental state and whose messages are typed INFORM/REQUEST/UNREQUEST primitives.

Concepts introduced/used: Agent-Oriented Programming, Mental State, Commitment, AGENT-0, Speech Act Theory, Agentification, BDI, Honesty Constraint

Stance: foundational

Relates to: Establishes the mentalistic ACL stance later criticised by Agent Communication Languages - Rethinking the Principles and surveyed by Intelligent Agents Theory and Practice; AGENT-0’s speech-act primitives anticipate KQML as an Agent Communication Language and FIPA-ACL; the mental-state architecture is reused in An Interaction-oriented Agent Framework for Open Environments.

Summary

A foundational survey that organizes the agent-based computing field into three tightly coupled concerns: agent theories (formal specifications of what an agent is, often via intentional notions such as belief, desire, intention, obligation), agent architectures (software/hardware designs satisfying those specifications, e.g., BDI, subsumption, layered), and agent languages (programming languages whose primitives embody the theorists’ concepts).

Wooldridge and Jennings distinguish a weak notion of agency (autonomy, social ability, reactivity, pro-activeness) from a stronger AI-centric notion involving mentalistic attributes (knowledge, belief, intention) and sometimes emotion or mobility. They review representational and reasoning formalisms (modal logics for knowledge and belief, intention logics), critique their computational tractability, and survey implementations (AGENT-0, PLACA, Concurrent METATEM). The paper sets the vocabulary used by much subsequent MAS research.

Conceptual Contribution

Claim: The emerging field of agent-based computing should be structured around the interlocking triad of agent theories, architectures and languages, and tensions between weak (behavioural) and strong (mentalistic) notions of agency should be kept explicit rather than elided.

Mechanism: Wooldridge and Jennings synthesise early 1990s work by (i) defining weak agency (autonomy, social ability, reactivity, pro-activeness) and strong agency (adds belief, desire, intention, emotion, mobility); (ii) surveying modal-logic theories of knowledge/belief/intention and the intentional stance as justification; (iii) cataloguing BDI, subsumption and layered architectures; and (iv) reviewing implemented languages (AGENT-0, PLACA, Concurrent METATEM) and representative applications. Computational tractability of the richer logics is flagged as a central open problem.

Concepts introduced/used: Weak Agency, Strong Agency, Intentional Stance, BDI, Subsumption Architecture, Layered Architecture, Concurrent METATEM, PLACA, Agent Theory-Architecture-Language Triad

Stance: survey

Relates to: Canonises the vocabulary used by Agent-Oriented Programming, Agent Communication Languages - Rethinking the Principles and Trends in Agent Communication Language; its tractability critique anticipates the social-semantic move in An Interaction-oriented Agent Framework for Open Environments.

PLACA

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