A Commitment-Based Approach to Agent Communication

Reference: Fornara, N. & Colombetti, M. (2004). Applied Artificial Intelligence 18(9–10): 853–867. DOI: 10.1080/08839510490509054. The journal article is paywalled; the open-access AAMAS-02 conference precursor — Operational Specification of a Commitment-Based Agent Communication Language (pp. 535–542) — captures the same model and is the locally archived source. Source file: fornara-colombetti-aamas02.pdf. URL

Summary

Fornara and Colombetti develop an object-oriented operational semantics for an Agent Communication Language grounded entirely in social commitments, intended for open environments populated by self-interested, heterogeneous agents who cannot be assumed to share an honest mental architecture. A Commitment is an abstract data type with fields Identifier, Debtor, Creditor, State ∈ {empty, cancelled, precommitment, conditional, active, fulfilled, violated}, Content (a temporal proposition), Condition (another temporal proposition), and Time-out. Its evolution is given by an explicit finite-state machine driven by two kinds of transitions: agent-invoked methods (mc, mp, ap, cc, cp, rp) and event-driven update rules triggered when the truth value of the content or condition resolves.

The authors’ key innovation over the Yolum-Singh treatment is the precommitment state, which models the social situation a directive speech act creates: the speaker cannot directly commit the hearer, so a request instantiates a precommitment whose debtor is the hearer; the hearer either accepts it (turning it into an active or conditional commitment), rejects it, fulfills it implicitly by performing the action, or lets the time-out elapse. This machinery yields uniform commitment-based definitions for Searle’s main illocutionary categories — assertives (inform, informIf, informRef), commissives (promise, conditionalPromise), and directives (request, conditionalRequest, accept, reject, yes/noQuestion, whQuestion) — and lets a propose act be defined compositionally as a conditional request conjoined with a conditional promise. A worked auction-style proposal protocol is given as an interaction diagram whose state contents are computed from the speech-act definitions, and whose soundness is checked by requiring that all final-state commitments be empty, fulfilled, or violated.

Key Ideas

Commitment-as-object: a commitment is an abstract data type with a state in {e, c, p, cc, a, f, v} whose dynamics are described by an explicit FSM.
Temporal proposition class: the content/condition of a commitment is a sentence + time interval + ∀/∃ mode + state, resolved by a domain “notifier” — separating what is committed from when and how its truth is observed.
Precommitment models directive speech acts: a request creates C(p, hearer, speaker, P|Q) that the hearer can accept (ap), reject (rp), implicitly fulfil (update rule 5), or let time out.
Conditional commitment with a temporal condition becomes active when the condition is satisfied and is automatically cancelled if the condition fails.
Five update rules link the truth-state of content and condition propositions to commitment-state transitions (active→fulfilled/violated, conditional→active/cancelled, precommitment→fulfilled).
Searle’s taxonomy of illocutionary acts is recovered by composition: inform, promise, request, accept/reject, yes/noQuestion, whQuestion, propose.
Soundness of an interaction protocol is checked by an interaction diagram in which every final state’s commitments are empty, fulfilled, or violated — a structural correctness criterion for negotiation protocols.
The notion of a conversational commitment (a meta-commitment to react to interlocutor speech acts) is sketched as the principled justification for the time-out field.

Connections

Conceptual Contribution

Claim: Speech-act semantics for an ACL should be specified operationally — as state-machine transitions over a public commitment data type — so that meaning is independent of any agent’s internal mental architecture, observable to third parties, and compositional across the speech-act taxonomy; in particular, the directive family requires a dedicated precommitment state because no agent can unilaterally commit another.
Mechanism: Define an abstract Commitment class with seven explicit states and a transition FSM driven by methods (mc/mp/ap/cc/cp/rp) plus five event-driven update rules that read truth-states of Temporal Proposition objects; define each Searle category by a single-line operation on commitment objects (inform := mc(a,b,P,T), request := mp(a,b,P,T), propose := conditionalRequest ∧ conditionalPromise, etc.); validate interaction protocols structurally via a state-content interaction diagram in which final-state commitments must all be empty/fulfilled/violated.
Concepts introduced/used: Commitment, Social Commitment, Precommitment, Conditional Commitment, Temporal Proposition, Commitment-Based Protocol, Commitment-based Semantics, Public Semantics, Verifiable Semantics, Speech Act Theory, Directives, Conversation Protocols, Interaction Protocols, Open Multi-Agent Systems, Conversational Commitment
Stance: formal-semantic / engineering
Relates to: Closest neighbour is Flexible Protocol Specification and Execution (Yolum & Singh, AAMAS-02) — the authors explicitly compare the two approaches: where Yolum-Singh use the Event Calculus and an abductive planner over create/discharge/cancel/release/assign/delegate, Fornara-Colombetti use an OO/FSM data type and add the precommitment apparatus to cover directives. Both belong to the social-semantics programme catalysed by ACL Rethinking Principles and formalised verifiability-style by Verifiable Semantics for ACLs; both are subsumed under the role-based unification of A Common Ontology Of ACLs. Repudiates the mentalistic line of FIPA-ACL / Intention Is Choice with Commitment for interoperable ACL semantics while keeping speech-act theory (Speech Acts - An Essay in the Philosophy of Language, A Taxonomy of Illocutionary Acts) as the organising taxonomy. The 2004 Applied AI version this entry primarily cites elaborates the AAMAS-02 model with extended treatment of negotiation protocols and the soundness-via-conversational-commitment programme that the authors’ later artificial-institutions work develops.

Tags

#acl #commitments #precommitment #speech-acts #protocol-specification #operational-semantics #foundational

Backlinks

Linked Pages

A Taxonomy of Illocutionary Acts

Reference: Searle, J. R. (1975). In K. Gunderson (Ed.), Language, Mind, and Knowledge (Minnesota Studies in the Philosophy of Science, vol. 7), pp. 344–369. University of Minnesota Press. Reprinted in Expression and Meaning (1979), CUP. Source file: searle_taxonomy_illocutionary_acts.pdf. URL

Summary

Searle develops a principled classification of illocutionary acts, replacing Austin’s intuitive five-category scheme (verdictive, expositive, exercitive, behabitive, commissive) with a taxonomy grounded in twelve significant dimensions of variation — chief among them illocutionary point, direction of fit (words-to-world, world-to-words, double, or null), and expressed psychological state (sincerity condition). Applying these criteria yields five basic classes: Representatives (assertions, conclusions — word-to-world fit, expressing belief), Directives (requests, commands — world-to-word fit, expressing want), Commissives (promises, threats — world-to-word fit, expressing intention), Expressives (thanks, apologies — null direction of fit, expressing various psychological states), and Declaratives (christenings, firings — double direction of fit, typically requiring an extra-linguistic institution).

Searle criticises Austin’s taxonomy for confusing illocutionary verbs with illocutionary acts (verbs are language-relative; acts are not), for overlap among categories, and for lacking a consistent principle of classification. The taxonomy became the standard reference for speech-act theory and, via agent communication language design, provided the fundamental performative vocabulary (tell, ask, promise, declare) inherited by KQML, FIPA-ACL, and later protocol work.

Key Ideas

Twelve dimensions of illocutionary variation; three central ones dominate.
Illocutionary point, direction of fit, expressed psychological state.
Five classes: Representatives, Directives, Commissives, Expressives, Declaratives.
Distinction between illocutionary verbs and illocutionary acts.
Declaratives depend on extra-linguistic institutions.
Critique of Austin: no single principle, verb/act conflation, overlap.
Sincerity conditions as essential to each class.

Connections

Conceptual Contribution

Claim: Illocutionary acts partition into exactly five basic classes (Representatives, Directives, Commissives, Expressives, Declaratives), determined by a small set of semantic dimensions (point, direction of fit, sincerity condition) rather than by surface verbs.
Mechanism: Enumerate twelve dimensions of variation; elevate three (illocutionary point, direction of fit, psychological state expressed) as primary axes; derive the five classes as equivalence classes under these axes; show Austin’s categories conflate verbs with acts and cross-cut the principled axes, producing overlap and miscategorisation (e.g., describe straddles representative/verdictive).
Concepts introduced/used: Illocutionary Point, Direction Of Fit, Sincerity Condition, Representatives, Directives, Commissives, Expressives, Declaratives
Stance: theoretical taxonomy
Relates to: Provides the performative vocabulary taken up by KQML, KQML as an Agent Communication Language, and downstream work on Agent Communication Languages; formalised further in Foundations Of Illocutionary Logic; offers the linguistic underpinning critiqued/extended by Agent Communication Languages - Rethinking the Principles and operationalised in Elephant 2000 - A Programming Language Based on Speech Acts.

Tags

Speech Acts - An Essay in the Philosophy of Language

Speech Acts: An Essay in the Philosophy of Language

Reference: John R. Searle (1969). Speech Acts: An Essay in the Philosophy of Language. Cambridge University Press. Source file: Searle 1969 - Speech Acts.pdf. URL

Summary

Searle’s foundational monograph gives speech-act theory its first systematic, philosophically defended treatment. Extending Austin’s How to Do Things with Words, it argues that the minimal unit of linguistic communication is neither the symbol nor the sentence but the production of the symbol in the performance of a speech act. Searle develops a constitutive-rule analysis of illocutionary acts, codifies the felicity conditions of paradigm acts (promising, referring, predicating, asserting), and uses the framework to attack the fact/value distinction, deriving “ought” from “is” via the institutional fact of promising.

The book introduces the now-canonical machinery that McCarthy’s Elephant 2000 - A Programming Language Based on Speech Acts imports as programming-language primitives: the force/content distinction F(p), propositional-content conditions, preparatory conditions, sincerity conditions, and essential conditions. It is also the direct ancestor of Foundations Of Illocutionary Logic, which formalises what Searle here develops discursively.

Key Ideas

Speech acts as the unit of meaning: producing a sentence under appropriate conditions is performing an illocutionary act; meaning reduces to a recursive theory of these acts.
Force vs. content F(p): every utterance factors into illocutionary force (assert, promise, request, …) and propositional content.
Constitutive rules: rules of the form “X counts as Y in context C” create institutional facts (promises, marriages) rather than merely regulating antecedent behaviour.
Felicity conditions for promising (canonical analysis): propositional-content, preparatory, sincerity, and essential conditions — the template every later ACL performative inherits.
Reference and predication as distinct speech acts, each with their own rules.
Institutional facts and the is/ought derivation via promising as a constitutive practice.

Connections

Elephant 2000 - A Programming Language Based on Speech Acts — McCarthy’s direct source for the speech-act vocabulary of Elephant
Foundations Of Illocutionary Logic — Searle & Vanderveken 1985, formalises the present book
Speech Act Theory
Speech Acts
Performatives
Illocutionary Force
Sincerity Conditions
Preparatory Conditions
Agent Communication And Institutional Reality
KQML
FIPA-ACL
Agent Communication Languages
Commitment-based Semantics

Conceptual Contribution

Claim: Linguistic communication is irreducibly act-theoretic: the minimal unit of meaning is the illocutionary act, analysable by constitutive rules and felicity conditions, and this analysis extends to reference, predication, and the generation of institutional facts.
Mechanism: Case studies of promising, referring, and asserting yield a recursive schema F(p) with four condition-types (propositional-content / preparatory / sincerity / essential). The schema is then redeployed to distinguish regulative from constitutive rules and to dissolve the classical is/ought problem by showing that uttering “I promise” institutionally constitutes an obligation.
Concepts introduced/used: Performatives, Illocutionary Force, Sincerity Conditions, Preparatory Conditions, Speech Act Theory, Institutional Reality, Commitment-based Semantics
Stance: foundational / philosophical
Relates to: Imported wholesale by Elephant 2000 - A Programming Language Based on Speech Acts as the philosophical basis for speech-act I/O; formalised by Foundations Of Illocutionary Logic; re-examined for multi-agent systems in Agent Communication And Institutional Reality and operationalised in KQML / FIPA-ACL performative sets. McCarthy explicitly departs from Searle by adopting a design stance on these primitives — see Abstract Performative.

Tags

Intention Is Choice with Commitment

Reference: Cohen, P.R. & Levesque, H.J. (1990). Artificial Intelligence 42(3): 213–261. Source file: cohen-levesque-intention-is-choice-with-commitment.pdf. URL

Summary

Cohen and Levesque formalise the “rational balance” that holds between an autonomous agent’s beliefs, goals, actions, and intentions. They define intention as a composite mental attitude: a persistent goal that the agent is committed to pursuing until it is achieved, known to be impossible, or no longer relevant. This yields a modal logic whose axioms capture Bratman’s three functional roles for intention — posing problems for means-end reasoning, acting as a screen of admissibility for future intentions, and prompting the agent to track (and re-try) the success of its actions.

The paper opens with the now-classic “Willie the robot” vignette (uncommitted, overcommitted, then homicidally committed), framing intention as what an agent must reason about to be both reliable and responsive. By relativising intentions to beliefs about another agent’s intentions the authors also sketch a theory of interpersonal commitment that anticipates speech-act and multi-agent communication semantics.

Key Ideas

Persistent goal (P-GOAL): a goal an agent will not drop until it is believed achieved, believed impossible, or its relevance condition fails.
Intention defined as a P-GOAL to have done an action while believing one is about to do it — closing Bratman’s gap between intending and acting intentionally.
Avoids the “side-effect problem”: agents don’t intend foreseen side-effects of their actions.
Mutual/relativised intentions as a foundation for interpersonal commitments and speech acts.
Desiderata list (beliefs, feasibility, non-futility, tracking) becomes a standard benchmark for intention logics.

Connections

Agent-Oriented Programming
Belief-Desire-Intention
BDI Logic
BDI Architecture
Joint Intentions
Commitment
Mental State
Rational Action Semantics
Speech Act Theory
Intentional Stance
Flexible Protocol Specification and Execution
A Commitment-Based Approach to Agent Communication
Communicative Actions for Artificial Agents - Cohen Levesque — the 1995 ICMAS sequel that turns the 1990 framework into an explicit speech-act / ACL semantics; direct ancestor of FIPA-ACL.
FIPA-ACL Specifications
Mentalistic Semantics
ACL Rethinking Principles — Singh’s critique of the BDI-based ACL semantics built on this foundation.

Conceptual Contribution

Claim: Intention is not a primitive mental state but a choice with commitment — a goal plus a meta-policy for when to drop it.
Mechanism: Modal logic over beliefs and goals plus a temporal operator for persistence; intention defined compositionally so its functional roles (planning, filtering, tracking) are theorems rather than axioms.
Concepts introduced/used: Persistent Goal, Commitment, Rational Balance, Mental State, Nested Beliefs, Joint Intentions.
Stance: foundational/formal.
Relates to: Shoham’s Agent-Oriented Programming cites this paper as the prime candidate for grounding AOP’s mental-state semantics; Shoham deliberately chooses a simpler obligation/commitment primitive for AGENT-0 but frames C&L as the rigorous theory AOP languages should eventually implement. The paper also underwrites FIPA-style Mentalistic Semantics and Rational Action Semantics for ACLs.

Tags

FIPA-ACL

The Foundation for Intelligent Physical Agents Agent Communication Language — a standardised successor to KQML, defining performatives with mentalistic semantics (beliefs/intentions of sender and receiver).

Primary source

FIPA-ACL Specifications — the canonical standards documents (FIPA00037 Communicative Act Library, FIPA00061 Message Structure)
Communicative Actions for Artificial Agents - Cohen Levesque — Cohen & Levesque 1995, the direct semantic ancestor

Discussed in

Agent Communication Languages
Speech Act Theory
Multi-Agent Systems
Mentalistic Semantics
Public Semantics
Commitment-based Semantics
An Ontology for Commitments in Multiagent Systems - Singh
CBCL - Safe Self-Extending Agent Communication — DCFL-bounded ACL with public-commitment semantics, addressing the unverifiability of FIPA-ACL’s mentalistic SL semantics

A Common Ontology Of ACLs

A Common Ontology of Agent Communication Languages: Modeling Mental Attitudes and Social Commitments using Roles

Reference: Boella, Damiano, Hulstijn, van der Torre (2006). Applied Ontology 3(1-3). Source file: ao07b.pdf. URL

Summary

The authors propose a common ontology that bridges two dominant semantic traditions for Agent Communication Langua mental-attitude-based semantics (FIPA-ACL) and social-commitment-based semantics (Singh, Colombetti). The unifying device is the role: each agent plays role instances in dialogue sessions, and both beliefs/intentions and commitments are attributed to role instances rather than to private mental states, sidestepping the unverifiability problem.

They develop Role-SL, a BDI logic extended with roles and dialogue sessions, and show translation schemes from FIPA speech acts and from actioandopositional commitment semantics into this role-based ontology. The framework accommodates mixed dialogues (e.g., persuasion intertwined with negotiation) that neither tradition handles cleanly alone.

Key Ideas

Roles as first-class carriers of public mental attitudes.
Role-SL: extension of FIPA-SL with role instances and dialogue sessions.
Mappings from FIPA-ACL and commitment-based ACLs into one ontology.
Public beliefs/intentions sidestep mental-state unverifiability.
Distinguishes action commitments (request/propose) from propositional (assert/challenge).

Connections

Conceptual Contribution

Claim: Mental-attitude and social-commitment ACL semantics can be unified under a common ontology by attributing both to roles instantiated in dialogue sessions, rather than to private agent minds.
Mechanism: Extends FIPA-SL into Role-SL (BDI + roles + dialogue sessions); provides translation schemes from FIPA speech acts and from action/propositional commitment semantics; handles mixed dialogues (persuasion + negotiation).
Concepts introduced/used: Roles, BDI, Commitment-based Semantics, Mental Attitudes, Mentalistic Semantics, Public Semantics, Verifiable Semantics, Dialogue Sessions, FIPA-ACL, Speech Act Theory, Ontologies, Agent Communication Languages
Stance: formal-semantic
Relates to: Bridges the two traditions typified by FIPA-ACL (mentalist) and Agent Communication And Institutional Reality (commitment-based); uses ontology machinery catalogued in Handbook On Ontologies.

Tags

Verifiable Semantics for ACLs

Verifiable Semantics for Agent Communication Languages

Reference: Michael Wooldridge (1998). ICMAS-98 (International Conference on Multi-Agent Systems). Source file: icmas98.pdf. URL

Summary

Wooldridge tackles a central problem for ACL standardization: how can an external observer verify that an agent conforms to an ACL’s semantics when semantics are expressed in modal BDI logic (beliefs, desires, intentions)? He formalizes an agent communication framework as a tuple containing agent programs, local states, a communication language, a semantic language, and interpretation functions, and defines precisely what it means for a framework to be verifiable: whether one can decide, from program text alone, that the semantic conditions for a sent message are satisfied.

He shows that KQML and FIPA-97 ACL, which define the “sincerity condition” for an inform act using multi-modal quantified logics like SL, are not practically verifiable — deciding whether an agent program really believes what it says requires checking undecidable properties. In contrast, he gives two example frameworks with verifiable (even co-NP-complete) semantics by grounding meaning in program states rather than unobservable mental attitudes. The paper’s upshot: practical ACL conformance testing requires public, state-based semantics.

Key Ideas

Formal agent communication framework as a 2n+4 tuple.
Verifiability = decidability of semantic conformance from program text.
KQML and FIPA-97 semantics (SL modal logic) are not practically verifiable.
Grounding semantics in program states yields co-NP-complete verifiability.
Motivates social/public commitment-based ACL semantics.

Connections

KQML
FIPA-ACL
Speech Act Theory
Agent Communication Languages
Verifiable Semantics
Public Semantics
Commitment-based Semantics
Mental State
Mentalistic Semantics
BDI
CBCL - Safe Self-Extending Agent Communication — O’Connor 2026: a verifiable ACL grounded in DCFL grammars and Lean-checked safety invariants, answering Wooldridge’s challenge in the LLM-agent era.

Conceptual Contribution

Claim: An ACL standard is only useful if one can check whether an implementation respects it; existing ACLs (KQML, FIPA-97) whose semantics are given in multi-modal BDI logics are not practically verifiable, so ACL semantics should instead be grounded in program states.
Mechanism: Formalises an agent communication framework as a (2n+4)-tuple of agent programs, local states, communication language L_C, semantic language L_S, and interpretations; defines verifiability as decidability (in polynomial time) of whether an agent program respects a message’s semantic precondition; shows FIPA’s SL semantics undecidable; constructs two verifiable example frameworks (classical propositional logic, grounded propositional epistemic logic) with co-NP-complete verification.
Concepts introduced/used: Verifiable Semantics, Agent Communication Framework, Sincerity Condition, Grounded Semantics, Program Semantics, Model Checking, BDI Logic, Mentalistic Semantics
Stance: formal-semantic / critique
Relates to: Formal companion to ACL Rethinking Principles — Singh’s social-agency argument becomes Wooldridge’s verifiability theorem. Undermines the semantic ambitions of KQML Overview and FIPA-ACL; motivates commitment-based approaches such as Agent Communication And Institutional Reality and the program-grounded framework in Foundations Of Illocutionary Logic.

Tags

ACL Rethinking Principles

Agent Communication Languages: Rethinking the Principles

Reference: Munindar P. Singh (1998). IEEE Computer, December 1998, pp. 40-47. Source file: computer-acl-98.pdf. URL

Summary

Singh surveys the state of Agent Communication Languages (ACLs) such as KQML and FIPA/Arcol, and argues that their dominant mental-agency semantics (defining communicative acts in terms of beliefs and intentions) is conceptually unsatisfying and practically untestable because we cannot read agents’ minds. He proposes a conceptual shift to social agency: ACL semantics should be grounded in a public perspective on commitments, roles, and societies, so compliance with the standard is observable and testable.

The paper maps the ACL design space along two critical dimensions — meaning (perspective, type, basis, context, coverage of communicative acts) and agent construction (design vs. execution autonomy) — and shows how both KQML and Arcol emphasize private, mental-state semantics and thus fail to enable true heterogeneous interoperation. Singh’s alternative emphasizes protocols, roles, and “society management” infrastructure as a richer public substrate for ACLs.

Key Ideas

Mental-agency ACL semantics (KQML, Arcol, early FIPA) cannot be verified without inspecting agent internals.
ACLs need a public perspective, conventional meaning, pragmatics, and full coverage of communicative act categories.
Seven categories of communicative acts: assertives, directives, commissives, permissives, prohibitives, declaratives, expressives.
Social agency replaces BDI with commitments, roles, and societies as the semantic basis.
Dialects/idiolects arise when only private perspectives are considered.

Connections

FIPA-ACL
FIPA-ACL Specifications
KQML
Speech Act Theory
Agent Communication Languages
Multi-Agent Systems
Communicative Actions for Artificial Agents - Cohen Levesque — the Mentalistic Semantics high-water mark Singh is critiquing
An Ontology for Commitments in Multiagent Systems - Singh — Singh’s own formal sequel: the four-place commitment ontology
Commitment Machines - Yolum and Singh
A Commitment-Based Approach to Agent Communication
Articulating Reasons - Brandom — the philosophical underwriting of public, commitment-based semantics
Making It Explicit - Brandom
Jones-Sergot Normative Systems — Counts-As Relation for institutional grounding of commitments
CBCL - Safe Self-Extending Agent Communication — O’Connor 2026: contemporary realisation of Singh’s social-agency programme (dialect installation as public commitment) in a Lean-verified LangSec-grounded ACL.

Conceptual Contribution

Claim: Agent Communication Language semantics must abandon mental agency (beliefs/intentions) and be grounded in a public, social perspective (commitments, roles, societies) in order to be testable and support heterogeneous interoperation.
Mechanism: Surveys KQML, Arcol, FIPA; lays out a two-dimensional design space (meaning × agent construction); shows that mental-state semantics cannot determine compliance; proposes social-agency framework using protocols, roles, and “society management” infrastructure.
Concepts introduced/used: Mentalistic Semantics, Public Semantics, Social Agency, Commitments, Communicative Acts, Verifiable Semantics, Interoperability, Dialects and Idiolects
Stance: critique / foundational
Relates to: Direct antecedent to Verifiable Semantics for ACLs (Wooldridge) which formalises the verification problem Singh names. Sharpens the critique of the mentalistic approach underlying KQML Overview and FIPA-ACL, and motivates commitment-based frameworks such as Agent Communication And Institutional Reality.

Tags

Event Calculus

A logic-based formalism (Kowalski & Sergot 1986; Shanahan’s planner formulation 2000) for reasoning about events that initiate and terminate fluents — properties whose truth value changes over time. Events are described by Initiates, Terminates, Happens, HoldsAt, Clipped, and Declipped predicates plus a small set of axioms.

In the agent-communication strand it is used to give an executable, planner-driven semantics to commitment-based protocols: each commitment is a fluent, each communicative act an event with Initiates/Terminates clauses, and protocol runs are abductively generated from initial- and goal-state descriptions.

In this vault

Flexible Protocol Specification and Execution

Flexible Protocol Specification and Execution: Applying Event Calculus Planning Using Commitments

Reference: Yolum, P. & Singh, M.P. (2002). Proceedings of the 1st International Joint Conference on Autonomous Agents and Multiagent Systems (AAMAS ’02), pp. 527–534. ACM, Bologna. Source file: yolum-singh-2002-flexible-protocol.pdf. URL

Summary

Yolum and Singh argue that finite-state-machine and Petri-net protocol formalisms over-constrain multi-agent interactions because they fix legal sequences of message tokens without regard to what those messages mean. They develop a commitment-based alternative in which each protocol action is reified as an operation on social commitments — Create, Discharge, Cancel, Release, Assign, Delegate — and the rules for how commitments evolve are formalised in a variant of the Event Calculus (Kowalski-Sergot, in Shanahan’s planner formulation). Base-level commitments C(x,y,p) and conditional commitments CC(x,y,p,q) become event-calculus fluents whose Initiates/Terminates clauses constitute the protocol specification.

The running example is the NetBill e-commerce protocol. Three reasoning postulates capture how a base-level commitment is discharged when its content holds, how a conditional commitment resolves into a base-level commitment when its precondition fires, and how CC is consumed when its consequent already holds. An abductive event-calculus planner (Shanahan) is then used to generate protocol runs from an initial state to a goal state, allowing agents to skip steps, reorder messages, or repair exceptions at runtime — provided every base-level commitment created during the run is eventually discharged. The result satisfies Singh’s three social-semantic desiderata: meaningful (content captured), verifiable (compliance checkable from public commitment trace), and declarative (specifies what each action achieves, not how to sequence actions).

Key Ideas

Commitment as fluent in event calculus: C(x,y,p) and CC(x,y,p,q) represented by the EC predicates Initiates, Terminates, HoldsAt, Happens, etc.
Six commitment operations (Create, Discharge, Cancel, Release, Assign, Delegate) compiled into Initiates/Terminates clauses.
Three postulates link content fluents to commitment fluents: discharging on content satisfaction, conditional-commitment resolution, and conditional consumption when consequent already true.
A protocol run is a sequence of Happens events; complete iff no base-level commitment is left holding — incomplete runs identify non-compliant agents.
Abductive planning (Shanahan) generates legal protocol runs from initial-state + goal-state descriptions, restoring autonomy/flexibility lost in FSM models.
Skipping steps and reordering (e.g. send-goods-before-accept) is supported because preconditions are over commitment state, not over a path through an FSM.
Permissions encoded via action preconditions; prohibitions encoded as commitments-not-to-bring-about.

Connections

Conceptual Contribution

Claim: Multi-agent protocols should be specified by the meaning of their actions — concretely, by how each action transforms the agents’ social commitments — rather than by legal token sequences; doing so simultaneously delivers meaningful, verifiable, and declarative semantics, and lets agents skip, reorder, or repair steps via runtime planning while still being held to their obligations.
Mechanism: Reify commitments as event-calculus fluents and define the six manipulation operations (Create/Discharge/Cancel/Release/Assign/Delegate) as Initiates/Terminates clauses; add three reasoning postulates governing base-level discharge and conditional-commitment resolution; use Shanahan’s abductive event-calculus planner to compute runs (sets of Happens clauses with a partial order) from initial states to goal states under the protocol’s preconditions; declare a run complete iff no base-level commitment is left holding, providing an objective compliance criterion.
Concepts introduced/used: Commitment, Conditional Commitment, Commitment-Based Protocol, Commitment-based Semantics, Event Calculus, Abductive Planning, Public Semantics, Verifiable Semantics, Conversation Protocols, Interaction Protocols, NetBill Protocol, Commitment Machines
Stance: formal-semantic / engineering
Relates to: Direct response to FSM- and Petri-net-based protocol traditions critiqued in ACL Rethinking Principles; supplies the operational machinery whose mentalistic counterpart (KQML/FIPA-SL) is shown unverifiable in Verifiable Semantics for ACLs. Companion to Singh’s social-agency programme and to the institutional-reality strand of Agent Communication And Institutional Reality. Conditional-commitment treatment derives from Colombetti’s earlier work and is contemporaneous with A Commitment-Based Approach to Agent Communication (Fornara & Colombetti AAMAS-02 / AAI-04), which gives a complementary object-oriented account of the same primitives (those authors note Yolum-Singh as the closest relative). Commitment-machine compilation to FSMs is the subject of the authors’ parallel ATAL-01 paper. Empire of mentalistic semantics from Intention Is Choice with Commitment is the foil — here intentions/persistence are not needed because the protocol semantics is exhausted by the public commitment trace.

Tags

Conversational Commitment

A meta-level commitment — sketched by Fornara & Colombetti and developed in Traum & Allen’s discourse-obligations work — that every agent makes when it agrees to take part in an interaction: the obligation to react in some way to the speech acts addressed to it. Conversational commitments justify structural features such as the time-out on a precommitment (the speaker is owed some reaction within bounded time) and underwrite soundness conditions for negotiation protocols.

In this vault

Open Multi-Agent Systems

MAS in which agents may join, leave, and act heterogeneously at runtime, with no central designer controlling their code or goals; demands public, verifiable semantics and robust trust/coordination mechanisms.

In this vault

Interaction Protocols

Specifications of legal conversation patterns (e.g. as Petri nets or state machines) above the message level.

In this vault

Conversation Protocols

Stateful, multi-turn interaction patterns (Contract Net, auction, query) specified as a finite automaton, Petri net, or role-based dialogue over performatives. Promote tractable ACL use by constraining expected message sequences, and are the unit on which ACRE’s reasoning engine operates.

In this vault

Directives

Searle: speech acts whose point is to get the hearer to do something (requests, commands, questions).

In this vault

A Taxonomy of Illocutionary Acts

Speech Act Theory

Philosophy-of-language framework (Austin, Searle, Vanderveken) in which utterances perform actions (illocutionary acts) — the semantic backbone of most Agent Communication Languages.

Sources

Foundations Of Illocutionary Logic — Searle & Vanderveken
Three Models for the Description of Language — Chomsky, foundations
Agent Communication And Institutional Reality

Applied in

Lineage

graph TD
  A["Austin (1962)<br/>How to Do Things with Words"] --> A1[Locutionary]
  A --> A2[Illocutionary]
  A --> A3[Perlocutionary]
  A2 --> S["Searle (1969, 1975)<br/>Speech Acts · Taxonomy of Illocutionary Acts"]
  S --> S1[Assertives]
  S --> S2[Directives]
  S --> S3[Commissives]
  S --> S4[Expressives]
  S --> S5[Declarations]
  G["Grice (1975)<br/>Logic and Conversation"] -.cooperative principle.-> S
  S --> V["Searle & Vanderveken (1985)<br/>Foundations of Illocutionary Logic"]
  V --> M["McCarthy (1989)<br/>Elephant 2000"]
  V --> KQML[KQML performatives]
  V --> FIPA[FIPA-ACL performatives]
  M --> FIPA
  KQML --> ACL[[Agent Communication Languages]]
  FIPA --> ACL

Papers: How to Do Things with Words · Speech Acts - An Essay in the Philosophy of Language · A Taxonomy of Illocutionary Acts · Logic and Conversation · Foundations Of Illocutionary Logic · Elephant 2000 - A Programming Language Based on Speech Acts

Verifiable Semantics

ACL semantics whose conformance can be checked against observable agent program state — the key demand behind moving from mentalistic to public semantics.

In this vault

Public Semantics

ACL semantics grounded in externally observable facts (commitments, roles, institutional state) rather than private mental state.

In this vault

ACL Rethinking Principles
Agent Communication And Institutional Reality
Commitment-based Semantics
Mentalistic Semantics
CBCL - Safe Self-Extending Agent Communication — dialect installation as a public commitment

Commitment-based Semantics

Approach that grounds ACL message meaning in public social commitments rather than private mental states — making conformance verifiable.

In this vault

ACL Rethinking Principles
Agent Communication Languages - Rethinking the Principles
Agent Communication And Institutional Reality
A Common Ontology Of ACLs
Public Semantics
Mentalistic Semantics
Flexible Protocol Specification and Execution
A Commitment-Based Approach to Agent Communication
CBCL - Safe Self-Extending Agent Communication — modern LangSec-grounded ACL inheriting Singh’s social-agency programme; dialect installation as public commitment

Commitment-Based Protocol

An interaction protocol specified not by a fixed message sequence but by the social commitments agents create, discharge, cancel or delegate through their messages. This gives an objective, verifiable semantics that tolerates flexible enactment.

In this vault

Temporal Proposition

An abstract data type used in Fornara & Colombetti’s commitment-based ACL to express the content or condition of a commitment. A temporal proposition has a statement (in some formal language), a time interval, a temporal mode (∀: must hold throughout the interval, or ∃: must hold at some point in the interval), and a state in {true, false, undefined}. A domain-specific notifier sets the state when the truth value resolves, which in turn drives the commitment’s update rules (active → fulfilled/violated, conditional → active/cancelled).

In this vault

Conditional Commitment

A commitment of the form if condition Q is satisfied, then debtor x is committed to creditor y for content P — written CC(x, y, P, Q) (Yolum-Singh) or C(cc, x, y, P|Q) (Fornara-Colombetti). When Q resolves to true the conditional commitment becomes an active base-level commitment C(x, y, P); when Q resolves to false it is cancelled. Conditional commitments are the workhorse for negotiation, conditional promises, proposals, and bidding in commitment-based ACL protocols.

In this vault

Precommitment

A distinguished state of a commitment object (Fornara & Colombetti 2002/2004) used to model the social situation a directive speech act sets up: because no agent can unilaterally place an obligation on another, a request from speaker a to hearer b creates a precommitment C(p, b, a, P|Q) whose debtor is the hearer. The hearer then either accepts (turning it into an active or conditional commitment), rejects (cancelling it), implicitly fulfils it by performing the requested action, or lets it expire after a time-out. Precommitment is what allows commitment-based ACL semantics to cover directives without retreating to mentalistic primitives.

In this vault

Social Commitment

A commitment treated as a public, social object — owned by the dyad of debtor and creditor and observable to third parties — rather than a private mental state of an individual agent. Social commitments are the central primitive of commitment-based ACL semantics: their lifecycle (created, conditional, active, fulfilled, violated, cancelled) is what an external observer monitors to verify protocol compliance. Castelfranchi 1995 is the foundational reference; Singh, Colombetti, Yolum, and Fornara give operational accounts.

In this vault

Commitment

A public, directed obligation from one agent to another to bring about some condition; commitments serve as the social-semantic alternative to mentalistic ACL semantics and ground protocol correctness in observable state rather than private beliefs.

In this vault

KQML

Knowledge Query and Manipulation Language — one of the first ACLs, developed in the early 1990s by the ARPA Knowledge Sharing Effort. Performative-based, separating content language from communication.

Primary sources

Agent Communication Languages
FIPA-ACL — the standardised successor
Speech Act Theory
Ontolingua Portable Ontology Specifications — companion Knowledge Sharing Effort project
A Common Ontology Of ACLs
Verifiable Semantics for ACLs
CBCL - Safe Self-Extending Agent Communication — modern DCFL-bounded ACL with the same performative/extensibility ambitions but formal safety guarantees

Speech Acts

Austin and Searle’s theory that utterances are actions performed in speaking — assertions, requests, promises, declarations — each defined by a force plus propositional content and by felicity conditions. Speech-act theory is the linguistic foundation of both KQML and FIPA performatives.

In this vault

Agent Communication And Institutional Reality

Agent Communication and Institutional Reality

Reference: Fornara, Viganò, Colombetti (2005). Agent Communication II, LNAI 3396, Springer. Source file: 978-3-540-32258-0_1.pdf. URL

Summary

Fornara, Viganò, and Colombetti propose regarding an Agent Communication Language as a set of conventions acting on a fragment of institutional reality, defined within an artificial institution. They reformulate commitment-based ACL semantics so that all commonly used communicative act types reduce to a single basic type, declarations, within a Basic Institution that regulates the lifecycle of social commitments.

Special institutions (e.g., English Auctions) extend the Basic Institution with ontological and normative elements. The approach is notable for making the semantics of speech acts publicly verifiable and independent of agents’ mental states, while retaining a uniform formal account of institutional actions and counts-as relations.

Key Ideas

ACL messages are institutional actions governed by counts-as rules.
Basic Institution manages creation/update/cancellation of social commitments.
All speech act types reducible to declarations within the institution.
Special institutions layer domain norms and ontologies on top.
English Auction given as worked example.

Connections

Conceptual Contribution

Claim: An ACL is best understood as a set of conventions operating on institutional reality; all communicative act types reduce to declarations within a Basic Institution that governs the lifecycle of social commitments.
Mechanism: Defines artificial institutions with counts-as rules; models message effects as declarations creating/updating/cancelling commitments; layers domain norms in Special Institutions (English Auction worked example).
Concepts introduced/used: Commitment-based Semantics, Institutional Reality, Counts-as Rules, Declarations, Performatives, Speech Act Theory, Public Semantics, Verifiable Semantics, Mentalistic Semantics, Ontologies, FIPA-ACL, Multi-Agent Systems
Stance: formal-semantic
Relates to: Offers the publicly-verifiable alternative to mental-state semantics of FIPA-ACL, which A Common Ontology Of ACLs then unifies via roles; grounded philosophically in Foundations Of Illocutionary Logic.

Tags

Commitment Machines - Yolum and Singh

Commitment Machines

Reference: Yolum, P. & Singh, M.P. (2002). Intelligent Agents VIII: Agent Theories, Architectures, and Languages (ATAL-01), LNAI 2333, pp. 235–247. Springer. (A preliminary version appeared in WET-ICE 2000.) Source file: yolum-singh-2002-commitment-machines.pdf. URL

Summary

Yolum and Singh propose commitment machines (CMs) as a protocol formalism that, unlike finite-state machines or Petri nets, attaches declarative meaning to states and actions in terms of the participants’ Social Commitments. A CM is a triple ⟨M, Δ, F⟩ of a finite minimal set of meanings (formulas in a propositional language extended with a commitment operator Cₓp and a strict-implication operator ;), a set of actions ⟨a : e⟩ whose effect e is itself a meaning, and a set of consistent final meanings. Transitions are not enumerated — they are inferred from the logical consequences of applying an action’s effect to the current meaning. The running example is the NetBill Protocol, specified by atomic propositions (request, goods, pay, receipt) and abbreviations for conditional commitments (accept = C_c(goods ; pay), promiseGoods = C_m(accept ; goods), etc.); three reasoning rules govern how commitments evolve as content propositions are made true.

The paper’s central technical contribution is a compilation procedure that turns any complete CM (one whose meaning set is closed under antecedence) into a deterministic FSM that can be executed in constant space without commitment reasoning at run time. The procedure is shown sound (Theorem 2 — every realised computation is generated by the source CM) and complete (Theorem 3 — every CM-generated computation has a semantically-strongest, efficient FSM-realised counterpart from true), via a chain of lemmas about semantic superiority, efficient computations, and endpoint equivalence. Because the meanings of states are explicit, agents executing the CM directly can plan paths through the protocol that exploit opportunities (e.g. a merchant proactively quoting without a request, “try before you buy” deals) and handle exceptions, recovering autonomy that pure-token FSM/Petri-net specifications eliminate.

Key Ideas

Commitment machine ⟨M, Δ, F⟩: state space is a finite minimal set of meanings (formulas) rather than tokens; actions ⟨a : e⟩ carry effect-meanings; final states are a consistent subset of meanings.
Inferred transitions: q ⊨_⟨a:e⟩ r iff (q ∧ e) ⊢ r — transitions are derived from logical entailment, not enumerated edges.
No fixed start state: a CM has no s₀; participants may begin from any meaning whose commitments they accept (typically true).
Three reasoning rules over commitments: (1) Cₓp discharges when p holds; (2) Cₓ(p ; r) collapses to base-level Cₓr when p holds; (3) Cₓ(p ; r) ceases when r holds before p, with no new commitment.
Compilation to deterministic FSM under two restrictions: (R1) no transition mᵢ → mⱼ if mᵢ ⊢ mⱼ (no information-free moves); (R2) the target meaning must dominate all alternatives entailed by the action (forcing maximal information).
Completeness requires “complete” CMs — meaning set closed under antecedence — so that a unique strongest target meaning always exists; trivially achieved by closing under conjunction.
Soundness, completeness, determinism established as theorems over the computation abstraction (sequences of meanings interleaved with actions); computations are compared by semantic superiority and endpoint equivalence rather than literal action-sequence equality.
Flexibility recovered for free: since states encode meanings, agents can skip steps, reorder, or take unsolicited shortcuts whenever the resulting meaning is still in M and the path to a final meaning still exists.

Connections

Conceptual Contribution

Claim: Multi-agent protocols should be specified by giving states and actions declarative meaning in terms of the participants’ commitments — not by enumerating legal token sequences — and any such specification can be soundly and completely compiled to a deterministic FSM, recovering executability without forfeiting flexibility, autonomy, or the ability to handle exceptions and exploit opportunities.
Mechanism: A propositional language with a commitment operator Cₓ and strict-implication ;; meaning sets M and final-meaning sets F (consistent w.r.t. logical consequence); action effects given as meanings; transitions inferred via (q ∧ e) ⊢ r. Compilation Procedure 1 maps ⟨M, Δ, F⟩ → ⟨S=M, Σ={a}, s₀=true, Q=F, δ⟩ under the two information-monotonicity restrictions; Procedure 2 promotes a computation to its semantically strongest counterpart, Procedure 3 removes redundant self-transitions, yielding efficient semantically-strongest computations that are realised by the compiled FSM. Soundness (Thm 2), determinism (Thm 1), and completeness for complete CMs (Thm 3) are proved.
Concepts introduced/used: Commitment Machines, Commitment-Based Protocol, Commitment-based Semantics, Conditional Commitment, Social Commitment, Public Semantics, Verifiable Semantics, NetBill Protocol, Endpoint Projection (structural analogue), Conversation Protocols, Speech Act Theory
Stance: formal-semantic / engineering
Relates to: Direct precursor and structural sibling of Flexible Protocol Specification and Execution (Yolum & Singh, AAMAS-02), which lifts the same six commitment operations (Create / Discharge / Cancel / Release / Assign / Delegate) into the Event Calculus and adds an abductive planner; ATAL-01 here is the FSM-compilation half of that programme. Companion to A Commitment-Based Approach to Agent Communication (Fornara & Colombetti, AAMAS-02 / AAI-04), which gives an OO/FSM operational semantics for the same primitives plus a precommitment state for directives. Carries forward the social-agency programme of ACL Rethinking Principles (Singh 1998) and answers Wooldridge’s challenge in Verifiable Semantics for ACLs by grounding meaning in publicly-observable commitment formulas rather than agent mental state. The Discussion explicitly contrasts with Smith et al.’s joint-intention–based protocols (mental constructs vs. social constructs) — the same fork that Intention Is Choice with Commitment anchors on the mental side. Structurally a direct analogue of choreographic Endpoint Projection: both compile a globally-specified protocol artefact to a per-role executable, the CM/FSM compilation losing declarative meaning for runtime efficiency much as endpoint projection loses the global view for distributable execution. This makes ATAL-01 the load-bearing reference for the constructive synthesis suggested in the Pact - A Choreographic Language for Agentic Ecosystems entry — choreographies could carry both communication structure (Pact-side) and a CM-style commitment trace (Singh-side), with one compilation step yielding both deadlock-freedom and conformance-checkability.