Kiko: Programming Agents to Enact Interaction Protocols

Reference: Samuel H. Christie V, Munindar P. Singh & Amit K. Chopra (2023). Proc. 22nd International Conference on Autonomous Agents and Multiagent Systems (AAMAS 2023), London, May 29 – June 2, 2023. IFAAMAS, 10 pages. Posted as arXiv:2606.26156v1 [cs.MA], 23 June 2026. URL. Software and appendix: https://gitlab.com/masr/bspl/-/tree/kiko

Summary

Kiko is a protocol-based programming model for agents that enact BSPL information protocols. Its diagnosis is that existing agent programming offers poor abstractions for decision making: JADE hard-wires FIPA’s ordering-based protocols, Jason and JaCaMo give cognitive abstractions but no protocols, commitment-based approaches lean on centralised commitment stores or do not operationalise asynchrony, and agent-oriented methodologies leave protocols as informal UML diagrams. Kiko’s answer is that the messages an agent sends are its public decisions, so the programmer’s job should reduce to writing decision makers: functions that are handed the set of messages the agent is currently enabled to send and choose which of them to complete and emit.

The enabling abstraction is the form: a prototype message instance whose ⌜in⌝ parameters are already bound from the agent’s history (its causal dependencies are met) and whose ⌜out⌝ parameters are left for the decision maker to fill. A generic protocol adapter computes the enabled forms from the agent’s local store, invokes decision makers on events, and validates each returned set of instances as an emission attempt: either every instance in the set is emitted or none is, so a decision maker that tries to send both Buy and Reject for one enactment is rejected outright rather than partially honoured. The adapter also validates receptions for integrity, and because BSPL constrains only emission, no ordering, reliability or central coordination is required of the transport; the implementation runs over UDP and treats reception as idempotent. Worked patterns include correlation across concurrent enactments, cross-enactment decisions (buy the cheapest of several quotes), playing roles in several unrelated protocols at once, atomic emission sets spanning protocols, reception-order freedom (a Rescind may overtake the Quote it depends on and simply disables the matching Buy), loose coupling under protocol change, and single-form decision makers as a convenient special case.

The formal part models an agent as a history plus input and output channels and gives a transition semantics with three rules: Recv (receive a message not already in the history if it passes the receive-check), Tx (delivery, whose non-application models loss) and Decide (compute enabled forms, apply a decision maker, emit if the send-check passes). Theorem 1 (soundness) states that every reachable state of a Kiko multiagent system simulates some reachable enactment of the protocol, so compliance holds regardless of what the decision makers choose; Theorem 2 shows that an optimised Decide rule that checks only the internal compatibility of the chosen set is equivalent to the full check, since forms are drawn from the enabled set and decision makers preserve their bindings; Theorem 3 (completeness) states that for any reachable enactment there exist decision makers that realise it, assuming all sent messages are received. The discussion relates Kiko to its predecessors in the same programme (Stellar, which introduced forms but used per-message handlers; Protocols over Things; Bungie; Mandrake), invokes the end-to-end argument for building over simple transports, and sketches norm-based forms, accountability, concurrent decision makers as actors, and microservices as directions.

Key Ideas

Messages are decisions. A protocol constrains decision making, not message ordering; an agent’s programming interface should be the set of valid decisions currently open to it.
Forms. Enabled message prototypes with ⌜in⌝ bound and ⌜out⌝ unbound, derived incrementally per enactment context (MAS identifier plus key bindings) from the local store.
Decision makers. Programmer-written functions from sets of forms to sets of instances; invoked on communication events by default, or on custom events via an internal queue, so no polling.
Atomic emission sets. An attempt is emitted in full or rejected in full; partial emission of a consistent subset is ruled out as arbitrary. This is the feature the authors call unique to Kiko.
Adapter architecture. Local Store, Enablement, Checker, Emitter and Receiver; the adapter is generic and understands information protocols, so the communication service is fully abstracted from business logic.
Unordered, lossy transport suffices. BSPL constrains only emission and reception is idempotent, so UDP without ordering or reliability enacts protocols correctly; this is offered as compatibility with the end-to-end argument, and as something ordering-based protocol approaches cannot claim.
Formal definitions. Association, instance, form, context, consistency, out- and nil-compatibility, derivation, enablement, decision maker, send-check and receive-check (Definitions 2 to 13).
Soundness, optimisation, completeness. Reachable states simulate protocol enactments (Thm 1); the internal-compatibility-only Decide is equivalent (Thm 2); any reachable enactment is realisable by some decision makers under delivery (Thm 3).
Loose coupling. Because coupling is by information, adding an indirect bank-transfer path to Purchase leaves the seller’s decision logic unchanged; the adapter derives the Deliver form once payment arrives by either route.
Lineage. Stellar (forms, message handlers), Protocols over Things and Mandrake (fault tolerance), Bungie (extensible application-level protocols), Tosca and Clouseau (commitments compiled to information protocols).

Connections

BSPL
Information Protocols
Enactability
BSPL - The Blindingly Simple Protocol Language
Semantics and Verification of Information-Based Protocols: defines the reachable enactments that Kiko’s states are shown to simulate
Interaction Protocols
Agent-Oriented Programming
AgentSpeak
An Interaction-oriented Agent Framework for Open Environments: the JaCaMo-based commitment framework Kiko contrasts with
Agents and Artifacts
FIPA-ACL Specifications: the JADE/FIPA ordering-based incumbent
Commitment-based Semantics
Actor Model: proposed substrate for concurrent decision makers
Multiparty Asynchronous Session Types: cited as a representative ordering-based protocol language
Endpoint Projection
CALM Theorem
CBCL - Safe Self-Extending Agent Communication

Conceptual Contribution

Claim: Agents should be programmed as sets of decision makers over the messages a protocol currently enables them to send. Given an information protocol, this abstraction guarantees compliance by construction, supports realistic decision patterns that ordering-based models cannot express, and needs only an unordered, unreliable transport.
Mechanism: Forms derived from the local store per enactment context; decision makers returning emission attempts checked atomically; a protocol adapter (store, enablement, checker, emitter, receiver) over UDP; an operational semantics (Recv, Tx, Decide) with soundness, an equivalent optimised check, and completeness relative to BSPL’s reachable enactments.
Concepts introduced/used: Information Protocols, BSPL, Enactability, Agent-Oriented Programming, Actor Model, Interaction Protocols
Stance: programming model / engineering, with formal guarantees
Relates to: Completes the BSPL stack begun in BSPL - The Blindingly Simple Protocol Language and Semantics and Verification of Information-Based Protocols by giving the agent side a programming interface whose correctness is stated against that semantics. It occupies the place that per-role projected programs occupy in Choreographic Programming and per-role monitors occupy in Session Types, but reaches it without Endpoint Projection: the adapter evaluates the global protocol against the agent’s own history. The same “decide from local history, verify from the trace” shape appears in CBCL - Safe Self-Extending Agent Communication’s R5 verifier, which is why Kiko and its BSPL lineage are the nearest multiagent-systems precedent for that work.

Tags

#agent-programming #interaction-protocols #bspl #information-protocols #decentralization #asynchrony #operational-semantics #aamas

Backlinks

Linked Pages

CBCL - Safe Self-Extending Agent Communication

CBCL: Safe Self-Extending Agent Communication

Reference: O’Connor, H. (2026). “CBCL: Safe Self-Extending Agent Communication.” 2026 IEEE Symposium on Security and Privacy Workshops (SPW), pp. 39–48. Preprint: arXiv:2604.14512v1 [cs.CR], 16 Apr 2026. Source file: oconnor-cbcl-langsec26.pdf. URL. Reference implementation: https://codeberg.org/anuna/cbcl-rs.

Summary

Building on McCarthy’s 1975/1982 Common Business Communication Language vision and the language-theoretic security programme of Sassaman, Patterson, Bratus and Locasto (Security Applications Of Formal Language Theory), this paper presents a contemporary CBCL: an agent communication language designed so that all messages — including runtime language extensions — remain within the deterministic context-free (DCFL) complexity class. The motivating diagnosis is that contemporary agent communication has slid up the Chomsky hierarchy without acknowledging the security cost: KQML and FIPA-ACL are CFL with informal extensibility, but MCP and LLM-based agent frameworks operate over inputs whose effective complexity is recursively-enumerable, where the validity of an arbitrary message is undecidable and “weird machines” (Exploit Programming - From Buffer Overflows To Weird Machines) become unavoidable. CBCL takes the opposite tack: minimal core (8 performatives — tell, ask, reply, hello, bye, ok, error, cancel) plus a homoiconic dialect mechanism that lets agents define, transmit, and adopt domain-specific vocabularies as first-class CBCL messages, with three machine-checked safety invariants — R1 (no recursion in dialect templates), R2 (declared resource bounds on depth, expansion size, verification time), R3 (core-vocabulary preservation) — that together guarantee DCFL preservation under arbitrary finite sequences of dialect installations.

The paper accompanies the design with a Lean 4 formalization (≈5,400 lines, 16 modules, 176 machine-checked theorems, zero sorry gaps, no custom axioms) covering parser correctness (soundness + completeness), R1–R3 verification, pipeline totality, and the central dcfl_preserved closure theorem; a verified parser binary cbcl-parse is extracted from the proofs. A separately-developed Rust reference implementation (cbcl-rs, ≈11,000 lines, no_std-compatible core) ships a hand-rolled O(n) parser, dialect verification engine, gossip-based dialect propagation (O(log n) convergence per Demers et al.), C FFI/WASM bindings, property-based and differential tests, and cargo-fuzz targets; differential tests cross-validate the Rust parser against the Lean-extracted binary, eliminating spec-implementation parser differentials. Five example dialects (precision agriculture, AI planning, cross-chain asset transfer, artifact management, email) are R1–R3-verified end-to-end. A draft IETF Internet-Draft specifying application/cbcl and a Nostr transport binding (cbcl-nostr) accompany the paper. The Discussion explicitly aligns the design with Singh’s social-agency programme: dialect installation is treated as a public commitment to the dialect’s declared semantics — semantic divergence becomes a breach of commitment, observable and accountable, rather than a hidden failure of shared mental state — sidestepping the unverifiable mentalistic semantics critique of Verifiable Semantics for ACLs.

Implementation status (post-paper, cbcl-rs). The reference implementation has shipped two further safety invariants the paper sketches as future work, plus a richer Lean formalisation: R4 (Integrity) — Ed25519-style signatures over canonical encodings via an algorithm-agnostic Signer trait, with three-valued install verdicts (Valid / Unsigned / Invalid) — and R5 (Contract Well-formedness) — optional (protocol …) and (shape …) clauses on a dialect, expressing causal Merkle DAG protocols and per-performative shape contracts; R5 enforces acyclicity, reachability from begin, performative definedness with ancestor closure for extends, step uniqueness, and depth-bound respect, all decidable in linear fuel at install time. The §VII-D structural-contracts vision is therefore live (SPEC-002, SPEC-003): verify_monotone, verify_all_is_meet, and verify_eventually_consistent are proved theorems showing causal-protocol verification is a lattice homomorphism that joins coordination-free under G-Set store merge — explicit CALM Theorem alignment. The Lean codebase has grown to 380+ declarations across 19 files (still zero sorry, only the standard axioms propext / Classical.choice / Quot.sound); the workspace ships 837 tests including 584 cbcl-core unit tests, 37 proptest cases, 21 differential integration tests against the Lean-extracted binary, libFuzzer harnesses, and cargo-mutants mutation testing at a 90% kill threshold. The crate layout has grown from the paper’s five to seven: the original cbcl-core / cbcl-parser / cbcl-cli / cbcl-wasm / cbcl-ffi plus cbcl-erl (Erlang/LFE binding, SPEC-009 — with SPEC-010 binding-conformance suite) and cbcl-arena (Agent Arena platform, SPEC-012 — composable referee on cbcl-lfe-router with capability-keyed message routing and signed receipt logs). A worked sealed-bid auction dialect (SPEC-004) demonstrates structural defence against false-claim manipulation — concrete evidence that the R5 contract layer is rich enough to encode mechanism-design integrity properties decidably. The earlier Scheme prototype (anuna-research/cbcl) is superseded; architecture decisions live as ADRs under .hence/ (purity boundary, parser library choice, error handling, WASM API surface, R4 adversarial review).

Key Ideas

DCFL as the Goldilocks complexity class: Regular is too weak for nested envelopes/dialects; general CFL admits ambiguous grammars and parser-differential attacks; context-sensitive is PSPACE-complete; Type-0 is undecidable. DCFL is the minimal class that supports nested structure with class-level unambiguity (parser equivalence under language evolution).
Homoiconic self-extension: Dialect definitions are themselves valid CBCL messages, parsed by the same recogniser used for ordinary communication — a single attack surface, no separate meta-language. Inspired by Racket’s #lang mechanism.
Three safety invariants R1–R3: declarative pattern-template substitution only (no recursion, no iteration, no reflection); declared resource bounds (depth ≤ 64, expansion ≤ 8192 chars, verification ≤ 1000 ms); the eight core performatives cannot be redefined.
DCFL preservation theorem: dialect invocations must appear inside a (lang name …) wrapper; the lang tag plus a unique dialect name forms a prefix-free partition that lets a deterministic pushdown automaton dispatch to the appropriate subgrammar without extra lookahead — circumventing the fact that DCFLs are not closed under union in general. Mechanised in Lean 4 as dcfl_preserved.
Lean 4 formalization with extraction: 176 theorems, 0 sorry gaps, no custom axioms; the verified parser binary cbcl-parse is extracted from the proofs and runs the same fuel-bounded recursive-descent parser as the model.
Rust reference implementation: cbcl-core (no_std, no unsafe), cbcl-parser, cbcl-cli, cbcl-ffi, cbcl-wasm. Differential tests against the Lean-extracted binary; cargo-fuzz over five entry points.
Eight core performatives (tell, ask, reply, hello, bye, ok, error, cancel) plus four message categories (simple, meta, lang-scoped, wrapped); keyword parameters in Common-Lisp style (:thread, :in-reply-to).
Single-pass template expansion: terminates in time linear in the template plus argument size; not Turing-complete; output is not fed back into the expander, ruling out unbounded re-expansion.
Epidemic dialect propagation: gossip-based with Demers et al.’s O(log n) convergence bound; agents independently verify R1–R3 and signatures before installing.
Canonical serialization per RFC 9804 for cryptographic operations — deterministic byte representation as a precondition for signature verification.
Dialect identity by content hash: name collisions resolved by canonical-form hash; downgrade attacks rejected at installation.
Self-expression vs self-adaptation (Zambonelli et al.): traditional ACLs support only parameter tuning within fixed structure; CBCL is a self-expressive protocol whose vocabulary structurally evolves under safety constraints.
Singh-aligned reading of dialect installation: a public commitment to declared semantics, with :examples clauses providing machine-checkable behavioural anchors — semantic divergence as observable breach rather than hidden mental-state mismatch.
Stated limitations: DCFL ceiling means no recursive transformations, no cross-field references (e.g. checksums over fields), no aggregation over variable-length collections, no context-sensitive validation. Standish-taxonomy paraphrastic only — no Orthophrase, no Metaphrase. Trust infrastructure (key distribution, revocation) and dialect-curation policy left to deployment.
Structural-contracts extension (sketched in §VII-D, shipped post-paper as R4 + R5): Ed25519-style dialect signatures plus protocol constraints as causal Merkle DAGs over performative-typed messages, with Visibly Pushdown Languages for shape constraints and coordination-free monotonic verification over an append-only store. Lean-mechanised lattice-homomorphism theorems (verify_monotone, verify_all_is_meet, verify_eventually_consistent) establish that replica verdicts join under G-Set merge.

Connections

Common Business Communication Language — McCarthy’s 1975/1982 origin; CBCL is the formally-verified realisation of that vision.
Security Applications Of Formal Language Theory — Sassaman et al.’s LangSec foundations.
Proof-Carrying Code - Necula — Necula 1997, the architectural ancestor of CBCL’s R4 split (host runs a small certified verifier; producer ships the proof).
Enforceable Security Policies - Schneider — Schneider 2000, the formal warrant for R5 monotone-verdict trace monitoring.
An Axiomatic Basis for Computer Programming - Hoare — Hoare 1969, root of the contract-based verification line CBCL inherits.
Authentication in Distributed Systems - Lampson Abadi Burrows Wobber — Lampson et al. 1992, the Speaks-For Calculus for delegated commitments.
Articulating Reasons - Brandom — Brandom 2000, the philosophical underwriting of Public Semantics (entry point).
Making It Explicit - Brandom — Brandom 1994, the full inferentialist treatise.
Empiricism and the Philosophy of Mind - Sellars — Sellars 1956, the Myth of the Given that makes Semantics-Without-Minds possible.
Philosophical Investigations - Wittgenstein — Wittgenstein 1953, Meaning As Use / language-games / rule-following.
Two Dogmas of Empiricism - Quine — Quine 1951, Semantic Holism.
Assertion - Stalnaker — Stalnaker 1978, Common Ground update semantics — operational analogue of CBCL’s verdict ledger.
Languages and Language - Lewis — Lewis 1975, Convention of Truthfulness picture of how an abstract language gets in force in a population.
Communicative Actions for Artificial Agents - Cohen Levesque — Cohen & Levesque 1995, the Mentalistic Semantics high-water mark CBCL deliberately is not.
FIPA-ACL Specifications — the engineering of FIPA-ACL (envelope, conversation-id, ontology slot) CBCL inherits; the semantics it replaces.
An Ontology for Commitments in Multiagent Systems - Singh — Singh 1999, the formal commitment ontology CBCL’s dialect contracts instantiate.
Jones-Sergot Normative Systems — Jones & Sergot 1993, the Counts-As Relation that gives wire events institutional meaning under a dialect contract.
Exploit Programming - From Buffer Overflows To Weird Machines — weird-machine analysis CBCL is designed to preclude at the parser layer.
PKI Layer Cake - Kaminsky Patterson Sassaman — concrete parser-differential attacks; CBCL’s class-level unambiguity rules these out at the grammar level.
The Halting Problems of Network Stack Insecurity
A Language-Based Approach To Prevent DDoS
LangSec
KQML as an Agent Communication Language
KQML - A Language And Protocol For Knowledge And Information Exchange
FIPA-ACL
ACL Rethinking Principles — Singh’s social-agency critique that CBCL’s “dialect installation as public commitment” inherits.
Agent Communication Languages - Rethinking the Principles
Verifiable Semantics for ACLs
A Common Ontology Of ACLs
Commitment-based Semantics
BSPL: Singh’s Information Protocols (AAMAS 2011) are the nearest multiagent-systems precedent for the R5 causal protocols and the R6 role layer: declarative, asynchronous, decentralised enactment from local history with no ordering assumptions. CBCL adds content-addressed predecessors, an adversarial threat model with signature-bound roles, the DCFL bound, runtime dialect installation, and a mechanised local-to-global correspondence; Enactability is the BSPL-side notion nearest to causal locality.
The State of the Art in Agent Communication Languages
Trends in Agent Communication Language
Toward Principles for the Design of Ontologies Used for Knowledge Sharing — Gruber’s ontological-commitment principle CBCL inherits.
Some Philosophical Problems from the Standpoint of Artificial Intelligence — McCarthy & Hayes’s representation/computation separation.
Elephant 2000 - A Programming Language Based on Speech Acts — McCarthy’s intra-program speech-act counterpart to CBCL’s inter-organisational vision.
Adjectival Modifiers
S-expression
Homoiconicity
Code as Data
Creating Languages in Racket — Flatt’s #lang mechanism that inspired CBCL’s homoiconic self-extension.
Extensibility in Programming Language Design - Standish
Language Extensibility Taxonomy
Paraphrase
Orthophrase
Metaphrase
Self-Expression
Self-Adaptation Self-Expression Self-Awareness ASCENS
Dialects and Idiolects
Keeping CALM - When Distributed Consistency is Easy — CALM theorem underwriting the forthcoming coordination-free contracts extension.
Visibly Pushdown Languages
MCP Landscape Security Threats And Future Research Directions
Survey Of AI Agent Protocols
Survey Of Agent Interoperability Protocols
ClawWorm Self-Propagating Attacks Across LLM Agent Ecosystems — concrete LLM-agent worm whose root-cause analysis CBCL’s lang-scoped provenance addresses.
Why AI Agents Communicate In Human Language
Why Do Multi-Agent LLM Systems Fail
Gossiping in Distributed Systems
Gossip-based Aggregation in Large Dynamic Networks

Conceptual Contribution

Claim: Agent communication languages can be simultaneously expressive, runtime-extensible, and tractably verifiable iff every message — including those that extend the language — is constrained to the deterministic context-free language class; this constraint is compatible with first-class self-extension, can be machine-checked end-to-end, and converts the unverifiable-mental-state problem of mentalistic ACLs into a public-commitment problem at the protocol layer.
Mechanism: Eight-performative core grammar (LL(1), DCFL); homoiconic dialect mechanism — dialect definitions are valid CBCL messages with extend clauses describing pattern-template substitutions; three safety invariants R1–R3 enforced at installation (no recursion via DFS cycle detection, declared resource bounds, core-vocabulary preservation); (lang name …) wrapper providing prefix-free deterministic dispatch into per-dialect sub-grammars so the union remains DCFL. Lean 4 formalization (LeanCbcl, ~5,400 LoC, 176 theorems) covering parser soundness/completeness, R1–R3, pipeline totality, and dcfl_preserved; verified parser extracted to a runnable binary (cbcl-parse). Rust reference implementation (cbcl-rs, ~11,000 LoC) with a ResourceContext-tracked single-pass expander, gossip-based dialect propagation (O(log n) per Demers et al.), canonical RFC-9804 serialization for signing, algorithm-agnostic Signer trait, C FFI / WASM bindings, property-based + differential tests, fuzz targets. Draft IETF application/cbcl Internet-Draft and Nostr transport binding.
Concepts introduced/used: Deterministic Context-Free Language, LangSec, Homoiconicity, S-expression, Dialects and Idiolects, Performatives, Self-Expression, Paraphrase, Orthophrase, Metaphrase, Visibly Pushdown Languages, CALM Theorem, Commitment-based Semantics, Public Semantics, Verifiable Semantics, Adjectival Modifiers, Ontological Commitment, Lean 4, Property-Based Testing, Parser Differential Attack, Weird Machine, Gossip Protocols, Canonical Serialization, Nostr, hence
Stance: engineering / formal-methods, with explicit position-taking on the agent-communication design space
Relates to: Realises McCarthy’s Common Business Communication Language vision (1975/1982) by giving formal safety guarantees McCarthy could only gesture at. Sits squarely in the LangSec programme of Security Applications Of Formal Language Theory and Exploit Programming - From Buffer Overflows To Weird Machines, extending it from input-validation analysis to protocol design — claiming, plausibly, to be the first ACL designed from LangSec principles and the first to demonstrate that LangSec is compatible with runtime self-extension. Inherits the DCFL-vs-ambiguous-CFG argument from PKI Layer Cake - Kaminsky Patterson Sassaman and applies it at the message layer rather than the certificate layer. Builds explicitly on Singh’s social-agency critique (ACL Rethinking Principles) and Wooldridge’s verifiability programme (Verifiable Semantics for ACLs) by treating dialect installation as a public commitment whose semantics are anchored by the :examples clause — a machine-checkable analogue of the commitment-trace conformance that Flexible Protocol Specification and Execution (Yolum & Singh) and Commitment Machines - Yolum and Singh establish for protocol actions. Where Pact - A Choreographic Language for Agentic Ecosystems takes the individual-rationality fork to answer “why follow a protocol?”, CBCL takes the publicness/verifiability fork: the meaning of a message is fully determined by the formal grammar plus declared semantics, with no mental-state inference required. Inherits Gruber’s ontological-commitment architecture but replaces “out-of-band agreement” with in-protocol propose/query/teach. The extensibility design draws on Creating Languages in Racket (Flatt’s #lang) and respects the boundary set by Extensibility in Programming Language Design - Standish: paraphrastic only, deliberately excluding orthophrase/metaphrase to keep the attack surface bounded. The forthcoming structural-contracts extension uses Visibly Pushdown Languages for shape constraints and the CALM Theorem for coordination-free verification — a natural bridge to commitment-machine semantics. The LLM-agent threat-model framing (ClawWorm Self-Propagating Attacks Across LLM Agent Ecosystems, MCP Landscape Security Threats And Future Research Directions) positions CBCL as the structural alternative to MCP/JSON-RPC-with-natural-language: same extensibility, vastly tighter security envelope.

Endpoint Projection

The mechanical translation from a global choreographic program — which describes the joint behaviour of all participants — to a per-participant local program that, when run in parallel with the others, realises the choreography. Endpoint projection is the operation that makes Choreographic Programming practical: the global program is the source of truth, and projection to each role is a syntactic/semantic transformation that preserves the communication structure and (under standard well-formedness conditions) deadlock-freedom. Implementations differ in how role information is tracked — type-system roles (Choral, ChoRus), census polymorphism (Bates et al. 2025), or algebraic-effect handlers (Pact, Effectful) — but all share the global-to-local move that distinguishes choreographic from session-typed programming. The structural analogue in commitment-based protocol theory is Commitment Machines, which compiles a global commitment specification to per-role finite-state machines. The multiagent-systems tradition also reaches decentralised endpoints by a route with no projection step at all: in BSPL Information Protocols every role acts directly on the global protocol using only its local history, and Enactability plays the part that projectability and knowledge of choice play here.

In this vault

Choreographic Programming
Structured Communication-Centred Programming for Web Services — origin of the Theorem of End-Point Projection
Multiparty Asynchronous Session Types — multiparty projection G ↾ p
Introduction to Choreographies
Session Types
Pact - A Choreographic Language for Agentic Ecosystems
Commitment Machines
Algebraic Effects
BSPL: decentralised enactment without projection; Enactability as the counterpart condition
Information Protocols

Session Types

A type discipline for communicating processes — originating with Honda (1993) and developed extensively by Honda, Vasconcelos, Yoshida, and others — in which a process’s communication behaviour is typed by a session type: a structured description of the sequence of messages that may flow on a channel, including alternation (!/?), choice (+/&), recursion, and delegation. Session types come in two flavours: binary (two participants per channel) and multiparty (a global type projected to per-role local types — directly analogous to choreographic Endpoint Projection). When a process can be source-checked, its session-type conformance is decidable statically; when it cannot, runtime monitors can enforce the type from observable message traces (On the Monitorability of Session Types). Structurally adjacent to the commitment-based protocol tradition: session types and Yolum-Singh-style commitment protocols are independently-developed formalisms for typing communicating agents against a publicly-observable global protocol.

In this vault

Multiparty Asynchronous Session Types — Honda, Yoshida & Carbone POPL 2008, the multiparty session-types foundation
Structured Communication-Centred Programming for Web Services — Carbone, Honda & Yoshida 2007/2012, choreographies built on session types
Introduction to Choreographies
On the Monitorability of Session Types
Choreographic Programming
Endpoint Projection
Commitment Machines - Yolum and Singh
BSPL: the multiagent-systems counterpart that dispenses with projection and ordered channels; Enactability in place of projectability
Flexible Protocol Specification and Execution
Conversation Protocols
Pact - A Choreographic Language for Agentic Ecosystems

Choreographic Programming

A programming paradigm in which a single global program describes the joint behaviour of all participants in a distributed protocol, and a mechanical endpoint projection derives the local program for each participant. Choreographic languages are designed so that well-typed choreographies are deadlock-free by construction — every send is matched by a corresponding recv in the projected counterpart. Originating in WS-CDL and formalised in the π-calculus / session-types community (Carbone, Honda, Yoshida), the paradigm has since been embedded in production languages (Choral for Java, ChoRus for Rust, HasChor for Haskell, Bates et al.’s census-polymorphic projection at PLDI 2025) and extended towards adversarial settings via cryptographic primitives (Sarkar & Russo; Veiga). Structurally adjacent to the Commitment-Based Protocol tradition: both specify protocols globally and project to local roles, but choreographic semantics is operational/communicational while commitment-based semantics is normative/social.

In this vault

Endpoint Projection
Structured Communication-Centred Programming for Web Services — Carbone, Honda & Yoshida ESOP 2007 / TOPLAS 2012, the foundational paper
Multiparty Asynchronous Session Types — Honda, Yoshida & Carbone POPL 2008, multiparty generalisation
Deadlock-freedom-by-design - Multiparty Asynchronous Global Programming — Carbone & Montesi POPL 2013, deadlock-freedom by construction across interleaved sessions
Introduction to Choreographies — Montesi 2023 (Cambridge), the canonical textbook
On the Monitorability of Session Types — Bartolo Burlò, Francalanza & Scalas ECOOP 2021, runtime monitoring
Session Types
Pact - A Choreographic Language for Agentic Ecosystems
Commitment-Based Protocol
Commitment Machines
Flexible Protocol Specification and Execution
Algebraic Effects

Semantics and Verification of Information-Based Protocols

Reference: Munindar P. Singh (2012). Proc. 11th International Conference on Autonomous Agents and Multiagent Systems (AAMAS 2012), Valencia, Spain, June 4–8, 2012. IFAAMAS. PDF. Semantic Scholar

Summary

The sequel to BSPL - The Blindingly Simple Protocol Language gives BSPL the formal semantics its flexibility demands, defines three correctness properties, and implements verifiers for them. A protocol denotes a set of enactments over a universe of discourse of roles and message schemas. Each role has a history of the messages it has emitted or received; a history vector collects one per role. Viability is the local rule from the 2011 paper made precise: a role may emit a message only if it knows the bindings of every ⌜in⌝ parameter for the enactment’s key and knows no binding for any ⌜out⌝ or ⌜nil⌝ parameter; reception is always viable and extends knowledge. The intension of a protocol is the set of history vectors that are viable, respect the fundamental causality constraint that a reception is preceded by the corresponding emission, and are covered by the intensions of the protocol’s references.

Three properties are then defined on the intension. A protocol is enactable if its intension is non-empty, that is, some viable path binds all public parameters. It is safe if no history vector binds the same parameter twice for the same key: safety is the distributed integrity property, and the paper’s diagnosis is that across roles it holds precisely when every pair of conflicting ⌜out⌝ emissions is gated by a causally prior branching point controlled by a single role. It is live if from any reachable state the enactment can still legally complete; liveness entails enactability but not the converse. The small examples fix intuitions: Local Conflict is safe but not enactable, Abrupt Cancel (a race between buyer and seller on outcome) is enactable but not safe, Purchase Unsafe drops the private parameter that made accept and reject exclusive, and Purchase No Ship is enactable but not live because after accept nothing can ever bind outcome.

For verification, a protocol’s causal structure is expressed as a set of declarative temporal precedence constraints, and each property is decided by checking the (un)satisfiability of the conjunction of that causal structure with a property-specific formula using a temporal reasoner. The paper reports the clause counts for Purchase and its variants and for the FIPA Request protocol, and lists cheaper design-flaw checks (deadwood messages, parameters that can never be bound or used). The related-work discussion positions BSPL against AUML, message sequence charts and choreography description languages, all of which take a procedural stance on ordering, and notes that both of Desai and Singh’s enactability failures, blindness and nonlocal choice, yield an empty intension and are thereby caught. The LoST middleware (local state transfer) is cited as the architecture that enforces the local constraints at runtime.

Key Ideas

Semantics by enactments. A protocol’s meaning is its intension: the set of viable, causally consistent history vectors covered by its references. Local views and asynchrony are built into the model rather than abstracted away.
Viability is local. Emission requires knowing all ⌜in⌝ bindings and no ⌜out⌝ or ⌜nil⌝ binding for the enactment key; the semantics of a protocol depends only on the specification, never on imagined internal policies of the agents.
Declarative force of ⌜out⌝. An ⌜out⌝ binding is not a report but a declaration (Austin), which is why it may occur only once per key and why a means clause can attach a commitment to it.
Enactability, safety, liveness. Non-empty intension; at most one binding per parameter per key across all roles; completion always remains possible. Liveness entails enactability.
Safety across roles needs a same-role branching point. Two conflicting ⌜out⌝ emissions by different roles are safe only if a causally prior conflict controlled by one role makes them exclusive; the private response parameter in Purchase is the canonical example.
Causal structures. The partial-order structure of a protocol as a set of temporal constraints, mappable to a finite-state machine only with an explosion in states, so reasoning is done declaratively instead.
Verification by satisfiability. Each property is a formula conjoined with the causal structure and handed to a temporal reasoner; validated on Purchase variants and FIPA Request.
Blindness and nonlocal choice both yield empty intensions, so the enactability check subsumes the earlier diagnostics of Desai and Singh.
Design-flaw checks. Deadwood messages, never-bound private parameters, never-used private parameters, protocols with public ⌜in⌝ parameters (empty intension).

Connections

BSPL
Information Protocols
Enactability
BSPL - The Blindingly Simple Protocol Language
Kiko - Programming Agents to Enact Interaction Protocols: the operational semantics whose soundness is stated relative to the reachable enactments defined here
Interaction Protocols
Commitment-based Semantics
Speech Act Theory: the declarative force of ⌜out⌝ bindings
FIPA-ACL Specifications: FIPA Request as a verification benchmark
Knowledge of Choice
Realizability and Verification of MSC Graphs
Deciding Choreography Realizability
Message Sequence Charts - A Survey
Multiparty Compatibility in Communicating Automata
Endpoint Projection
CBCL - Safe Self-Extending Agent Communication

Conceptual Contribution

Claim: An information-based protocol language can be given a formal semantics that respects the locality of each role, the flow of causality across roles and the asynchrony between them, and its central correctness properties (enactability, safety, liveness) can be formulated declaratively and verified mechanically.
Mechanism: Universe of discourse, role histories, history vectors, viability, and intension by cover; Definitions of enactability (non-empty intension), safety (key uniqueness in every history vector) and liveness (completion always possible); causal structure as temporal precedence clauses; verification by (un)satisfiability with a temporal reasoner; evaluation on Purchase variants and FIPA Request.
Concepts introduced/used: Enactability, Information Protocols, BSPL, Realizability, Knowledge of Choice, Interaction Protocols
Stance: formal semantics / verification
Relates to: Enactability is the multiagent-systems analogue of the Realizability problem for message sequence charts and choreographies (Realizability and Verification of MSC Graphs, Deciding Choreography Realizability) and of Knowledge of Choice in Choreographic Programming: all ask whether independently acting endpoints can jointly produce exactly the specified global behaviour. BSPL’s answer is stated over local knowledge rather than channel orderings, which is also the reading that the CBCL role layer’s causal-locality condition takes (CBCL - Safe Self-Extending Agent Communication, Endpoint Projection).

BSPL - The Blindingly Simple Protocol Language

Information-Driven Interaction-Oriented Programming: BSPL, the Blindingly Simple Protocol Language

Reference: Munindar P. Singh (2011). Proc. 10th International Conference on Autonomous Agents and Multiagent Systems (AAMAS 2011), Taipei, Taiwan, May 2–6, 2011, pp. 491–498. IFAAMAS. URL. PDF

Summary

Singh introduces BSPL, a declarative language for multiagent interaction protocols built from exactly two constructs: a message schema (a single message is an atomic protocol) and the composition of existing protocols. The paper’s programme is interaction-oriented programming (IOP): treat the protocol as an engineering abstraction in its own right, specify it in terms of the information it needs in order to proceed and the information it produces when enacted, and let agents be independently designed and operated, judged only by their participation in the specified interactions. BSPL states no constraints on the ordering or occurrence of messages. Every ordering and exclusion requirement that a traditional protocol notation would express with control-flow or choice operators is instead derived from the information model of the messages.

The mechanism is parameter adornment. Each protocol and each message carries parameters, and each parameter is adorned ⌜in⌝ (its binding must come from outside, that is from a prior message), ⌜out⌝ (its binding originates here, with declarative force) or ⌜nil⌝ (the sender must not know a binding at emission time). Some parameters are marked as the key: a key binding identifies an enactment, and any parameter may be bound at most once per key binding. From these follow BSPL’s three commitments to the relational view of protocols as tables of enactments: uniqueness (one enactment per key), integrity (every public parameter bound in a complete enactment) and immutability (bindings never change, which is what makes the design robust to asynchrony). Ordering emerges as ⌜out⌝-before-⌜in⌝ on a shared parameter; mutual exclusion emerges as two messages both adorning the same parameter ⌜out⌝ for the same key; conventional orderings that carry no information (pay before delivery) are captured by introducing a token parameter. Composition renames parameters through references, so the foreign-exchange case study (bilateral price discovery composed with itself into multilateral price discovery, from Desai et al.) needs no access to the constituents’ internals, unlike the AUML nesting and data-flow-axiom approaches it is compared against.

The semantics is sketched rather than formalised (that is the work of Semantics and Verification of Information-Based Protocols). A role’s history is the sequence of messages it has sent or received; a history vector collects one history per role; it is quiescent when every sent message has been received and viable when every emission was made by a role that knew all ⌜in⌝ bindings and no ⌜out⌝ or ⌜nil⌝ binding at the time. A protocol’s intension is its set of quiescent viable history vectors. Three conflict kinds organise correctness: ⌜out⌝–⌜in⌝ (ordering, handled by causality), ⌜nil⌝–⌜in⌝ and ⌜nil⌝–⌜out⌝ (knowledge, local to one role) and ⌜out⌝–⌜out⌝ (occurrence, which has no general solution but can be checked to be under one role’s control). Meaning is deliberately separated from structure: a means clause may attach a commitment to a message, and BSPL is offered as the operational substrate that commitment-based approaches such as Commitment Machines - Yolum and Singh previously lacked.

Key Ideas

Two constructs only. A protocol is one message schema or a composition of protocols; there is no distinction between atomic and composite protocols, and no sequence, choice or loop operator.
Information orientation and explicit causality. Every causal dependency is an information dependency: a message can be sent only when its ⌜in⌝ parameters are already bound in the sender’s local history. There are no hidden flows of causality because there are no hidden flows of information.
Adornments ⌜in⌝ / ⌜out⌝ / ⌜nil⌝ and keys. Adornments are relative to the protocol, not to a role. A top-level enactable protocol adorns all public parameters ⌜out⌝; a protocol with a public ⌜in⌝ parameter is not enactable on its own and must be composed.
Uniqueness, integrity, immutability. Enactments are immutable tuples keyed by the key parameters; a parameter bound twice for the same key is an integrity violation, which is how exclusive choice is expressed.
Shared-nothing enactment. No global state or repository is needed: everything relevant to the social state of an interaction is in the parameter bindings of the messages exchanged. Each agent acts from its local history alone.
Ordering and exclusion are derived. ⌜out⌝ precedes ⌜in⌝ on the same parameter; two ⌜out⌝ adornments of the same parameter make the messages mutually exclusive; ⌜nil⌝ forces a message before a role learns a binding.
Specification patterns. Duplicating a parameter, generating an identifier, local (hidden) parameters, standing offers with composite keys (Insurance Claims), flexible sourcing of ⌜out⌝ parameters, in-out polymorphism (an unadorned parameter accepts either direction), forwarding, mixed initiative, and digressions in the sense of Yolum and Singh.
Composition without breaking encapsulation. Multilateral price discovery is a composition of the generalised bilateral protocol with itself, with adornments in the two references doing the coordination work that Desai et al.’s data-flow axioms and Odell et al.’s AUML nesting required.
Comparison with procedural notations. Choreographies (WS-CDL, message sequence charts), AUML and RASA specify orderings directly; BSPL avoids the enactability failures Desai and Singh call blindness because the only way to state an ordering is a causally sound ⌜out⌝-to-⌜in⌝ flow. Nonlocal choice is not automatically avoided but is analysable.
Meaning stays separate. means clauses attach commitments to messages; BSPL supplies the operational underpinning that meaning-based protocol approaches assumed.
Named future work. Multiple keys, compositional verification of enactability, multicast (several agents playing one role) and discovery protocols with late role binding. Kohei Honda is thanked in the acknowledgements, a direct line to the Session Types tradition.

Connections

BSPL (concept hub)
Information Protocols
Enactability
Interaction Protocols
Semantics and Verification of Information-Based Protocols: the formal semantics and verifier for this language
Kiko - Programming Agents to Enact Interaction Protocols: the programming model built on it
Commitment Machines - Yolum and Singh
Flexible Protocol Specification and Execution
Commitment-Based Protocol
Commitment-based Semantics
ACL Rethinking Principles: the same author’s earlier argument for public, protocol-based ACL semantics
FIPA-ACL Specifications: the ordering-based interaction protocols BSPL positions itself against
Coordinating Agents Using ACL Conversations
Endpoint Projection
Session Types
Multiparty Asynchronous Session Types
Choreographic Programming
Knowledge of Choice
Realizability and Verification of MSC Graphs: the nonlocal-choice problem BSPL inherits from message sequence charts
Message Sequence Charts - A Survey
Declarative Specification
CALM Theorem: monotone local knowledge as the basis for coordination-free enactment
CBCL - Safe Self-Extending Agent Communication: the nearest contemporary relative; see the contrast on BSPL

Conceptual Contribution

Claim: Multiagent protocols can be specified without any control-flow constructs. Modelling messages by the information they require and produce, with adornments and keys, yields all necessary ordering and exclusion constraints, supports shared-nothing asynchronous enactment from local knowledge, composes without breaking encapsulation, and leaves meaning to a separate layer.
Mechanism: Message schemas with ⌜in⌝/⌜out⌝/⌜nil⌝ parameter adornments and key parameters; protocol composition by reference with parameter renaming; a relational reading of enactments (uniqueness, integrity, immutability); a sketched semantics of quiescent viable history vectors; a conflict taxonomy (ordering, knowledge, occurrence); a foreign-exchange case study against Desai et al.’s commitment-protocol formalisation.
Concepts introduced/used: Information Protocols, BSPL, Enactability, Interaction Protocols, Declarative Specification, Commitment-based Semantics, Knowledge of Choice, Realizability
Stance: language design / foundational
Relates to: Continues Singh’s programme from ACL Rethinking Principles (public, verifiable protocol semantics instead of mental states) and supplies the operational layer under Commitment Machines - Yolum and Singh and Flexible Protocol Specification and Execution. It is the multiagent-systems counterpart to Multiparty Asynchronous Session Types and Choreographic Programming: where those derive per-role behaviour from a global type by Endpoint Projection and presuppose a compiler and ordered channels, BSPL has no projection step at all, because every role acts directly on the global protocol using only its own history over an unordered transport. CBCL - Safe Self-Extending Agent Communication later arrives at a similar causal, coordination-free protocol layer from the LangSec side, with content-addressed predecessors and signatures in place of parameter keys.

Interaction Protocols

Specifications of legal conversation patterns above the message level. Three families: ordering-based (Petri nets, state machines, AUML, FIPA interaction protocols), type-based (Session Types, Choreographic Programming with Endpoint Projection), and information-based (BSPL Information Protocols, where ordering and exclusion are derived from what each message requires and produces). Commitment-Based Protocols layer meaning over any of them.

In this vault

Actor Model

Hewitt’s concurrency model: isolated actors communicating by asynchronous messages, spawning new actors, and changing local behaviour.

In this vault

Agent-Oriented Programming

Reference: Shoham, Y. (1993). Artificial Intelligence 60, Elsevier. Source file: shoam-aop.pdf. URL

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.

Key Ideas

AOP as OOP specialization with mental-state components.
Agents constrained by honesty/consistency on communicative acts.
Speech-act-typed primitives as message types.
AGENT-0 language and interpreter.
“Agentification” of arbitrary devices.

Connections

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.

Tags

Enactability

The property that a protocol can actually be carried out by independently acting roles. In BSPL (Semantics and Verification of Information-Based Protocols) a protocol is enactable if and only if its intension is non-empty: there exists a viable history vector, built from emissions each of which the sending role could make from its own knowledge at the time, that binds every public parameter. A protocol with a public ⌜in⌝ parameter is not enactable standalone; Local Conflict, in which two messages from the same role both bind the key, is not enactable because emitting one disables the other. Enactability is entailed by liveness (completion always remains possible) but is weaker than it, and is independent of safety (no parameter bound twice per key).

Desai and Singh’s earlier diagnostics of unenactable business protocols, blindness (a role required to act on information it never receives) and nonlocal choice (two roles free to make incompatible choices), both yield an empty intension, so the single check subsumes them. Enactability is the multiagent-systems counterpart of Realizability for message sequence charts and choreographies (Realizability and Verification of MSC Graphs, Deciding Choreography Realizability) and of Knowledge of Choice and projectability in Choreographic Programming and Session Types: all ask whether local views suffice for the global specification. Stated over local knowledge rather than channel orderings, it is also the closest existing notion to the causal-locality condition under which the CBCL role layer’s Endpoint Projection is sound (CBCL - Safe Self-Extending Agent Communication).

In this vault

BSPL

The Blindingly Simple Protocol Language, Munindar Singh’s declarative language for multiagent interaction protocols (AAMAS 2011) and the reference instance of Information Protocols. A BSPL protocol is a set of message schemas and references to sub-protocols; every parameter is adorned ⌜in⌝ (must already be known to the sender), ⌜out⌝ (bound, with declarative force, by this message) or ⌜nil⌝ (must not yet be known), and a subset of parameters forms the key that identifies an enactment. There are no sequence, choice or loop operators: ordering follows from ⌜out⌝-before-⌜in⌝ on a shared parameter, and exclusive choice from the rule that a parameter is bound at most once per key. Enactment is shared-nothing and asynchronous: each agent decides what it may send from its own history alone, over a transport that need be neither ordered nor reliable, with no central coordinator.

The programme runs from language (BSPL - The Blindingly Simple Protocol Language) through formal semantics and verification of Enactability, safety and liveness (Semantics and Verification of Information-Based Protocols) to programming models for agents (Kiko - Programming Agents to Enact Interaction Protocols, preceded by Stellar, Protocols over Things, Bungie and Mandrake in the same group). The LoST middleware (local state transfer, 2011) is the architectural style; Splee (2017) extends the language with sets and expressions; Tosca (2017) and Clouseau (2020) compile commitment specifications down to information protocols; Chopra, Christie and Singh’s JAIR 2020 evaluation of protocol languages is the group’s own comparative survey.

Relation to session types and choreographies. Multiparty Asynchronous Session Types and Choreographic Programming derive per-role behaviour from a global type by Endpoint Projection and presuppose a compiler, fixed roles and ordered channels. BSPL reaches decentralised enactment without a projection step: every role acts on the global protocol using only its local history, and enactability plays the part that projectability and Knowledge of Choice play on the session-type side. It shares the nonlocal-choice problem with message sequence charts (Realizability and Verification of MSC Graphs) but detects it as an empty intension.

Relation to CBCL. CBCL - Safe Self-Extending Agent Communication’s R5 causal protocols and its later role layer are the nearest contemporary relative: declarative, asynchronous, decentralised verification from local history with no ordering assumptions, in Singh’s public-commitments tradition (ACL Rethinking Principles). The differences are what CBCL adds: dependencies are content-hash edges to concrete message instances rather than parameter values, the threat model is adversarial with roles bound by nomination and signature, the message language is bounded to DCFL, dialects install at runtime, and the local-to-global correspondence is a mechanised theorem rather than a tool-checked property. Any comparison with session types owes BSPL the same paragraph.

In this vault

BSPL - The Blindingly Simple Protocol Language (Singh, AAMAS 2011)
Semantics and Verification of Information-Based Protocols (Singh, AAMAS 2012)
Kiko - Programming Agents to Enact Interaction Protocols (Christie, Singh & Chopra, AAMAS 2023)
Information Protocols
Enactability
Interaction Protocols
Commitment Machines - Yolum and Singh
Commitment-Based Protocol
Commitment-based Semantics
ACL Rethinking Principles
Endpoint Projection
Session Types
Choreographic Programming
Knowledge of Choice
CALM Theorem
CBCL - Safe Self-Extending Agent Communication

Information Protocols

Interaction protocols specified purely by the information that messages require and produce, with no control-flow constructs. Introduced by Singh with BSPL: each message schema names a sender role, a receiver role and parameters adorned ⌜in⌝, ⌜out⌝ or ⌜nil⌝, and a key subset of parameters identifies the enactment. Two constraints do all the work. Information causality: a message may be emitted only when its ⌜in⌝ parameters are already bound in the sender’s local history, so ordering is derived rather than stated. Information integrity: within one enactment (one key binding) a parameter may be bound at most once, so exclusive choice is derived rather than stated. Because both constraints are evaluated against local history and bindings are immutable, enactment is coordination-free and tolerates unordered, lossy delivery; a received message is either consistent with the local store and added, or rejected.

The paradigm’s correctness vocabulary is Enactability (some viable path completes the enactment), safety (no parameter bound twice per key across all roles) and liveness (completion always remains possible). Its programming counterpart is the form, an enabled message with its ⌜in⌝ parameters filled and its ⌜out⌝ parameters awaiting a decision (Kiko - Programming Agents to Enact Interaction Protocols). Meaning is layered separately: a means clause may attach a commitment to a message, connecting information protocols to Commitment-based Semantics.

Contrast with ordering-based specifications (FIPA-ACL interaction protocols, AUML, message sequence charts, WS-CDL) and with type-based ones (Session Types, Choreographic Programming), which fix sequences or derive local behaviour by Endpoint Projection. CBCL - Safe Self-Extending Agent Communication’s causal protocols are the content-addressed, adversarial-setting relative of this idea.

In this vault

CALM Theorem

Consistency As Logical Monotonicity (Hellerstein 2010 conjecture; Ameloot, Neven, Van den Bussche 2013 proof). A distributed program has a consistent, coordination-free implementation if and only if it is expressible in monotonic logic.

Monotonic programs produce a set of outputs that only grows as inputs arrive (S ⊆ T ⟹ P(S) ⊆ P(T)). Such programs are safe under missing information: any conclusion reached on a subset of inputs remains valid when more arrive. Non-monotonic programs may retract earlier conclusions, so they must wait for “all the news” — which is what distributed coordination enforces.

CALM is the positive counterpart to the CAP Theorem: it names the exact class of programs that can satisfy Consistency, Availability, and Partition-tolerance simultaneously.

Why it matters

Moves consistency from a property of storage (linearizability, serializability) to a property of programs — Confluence.
Tells programmers what kinds of features are free (monotonic: set union, counting up, set-containment) and what must be paid for (non-monotonic: set difference, strict aggregation, count-exact, deletions without tombstones).
Gives a design rule for coordination-free systems: build from monotonic primitives — CRDTs, Immutable Data Structures, Tombstones, monotonic accumulators — and only add coordination at non-monotonic boundaries.

Formal statement

Using Relational Transducer networks as the execution model and Confluence as the consistency criterion, Ameloot et al. prove: a query Q has a coordination-free distributed evaluation plan iff Q is monotone.

In this vault

Keeping CALM - When Distributed Consistency is Easy — the definitive survey
CAP Theorem
Confluence
Monotonic Logic
Coordination Avoidance
Relational Transducer
Bloom Language
Dedalus
CRDTs
Non-monotonic Reasoning

Multiparty Asynchronous Session Types

Reference: Honda, K., Yoshida, N. & Carbone, M. (2008). Proceedings of the 35th Annual ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages (POPL ’08), San Francisco, CA, pp. 273–284. ACM. DOI: 10.1145/1328438.1328472. Journal version: Journal of the ACM 63(1):9, 2016, DOI: 10.1145/2827695. Source file: honda-yoshida-carbone-popl08.pdf. URL

Summary

Honda, Yoshida and Carbone generalise the binary session-type discipline of Honda (1993) and Honda-Vasconcelos-Kubo (1998) to multiparty asynchronous communication: a single global type describes the interaction protocol among N ≥ 2 participants, and per-participant local types are derived by a syntactic projection function that translates each global statement into the participant’s local view of it. A process calculus extending the asynchronous π-calculus is typed against these local types; the central technical result is the subject reduction and progress theorem: a system of well-typed processes is deadlock-free, communication-safe (no message-type mismatch), and session-fidelity-preserving (the runtime trace conforms to the global type, projected). This three-tier structure — global types, local types via projection, processes typed against local types — is the formal foundation that the entire contemporary multiparty session-types and choreographic-programming literature inherits.

The paper’s intellectual contribution is to make the global protocol a typed object whose well-formedness can be checked once, with the well-typedness of every projected role following automatically. Where binary session types describe the obligations of two endpoints separately and rely on duality, multiparty session types describe the joint protocol once and project to as many roles as needed, with a coherence condition (each branching point is observed by every relevant participant) ensuring projections are mutually consistent. The treatment is asynchronous: send is non-blocking, messages are buffered in per-channel queues, and the type system tracks the resulting message-order obligations. The framework is the direct precursor of contemporary choreographic-programming languages (Choral, HasChor, ChoRus, Pact) and of the runtime-monitoring theory developed in On the Monitorability of Session Types.

Key Ideas

Global type: a single typing artefact G describing the interaction among N participants — primitives include p → q : ⟨S⟩.G (participant p sends a value of type S to q, then G), branching p → q : {ℓᵢ : Gᵢ}, recursion μt.G, and parallel composition.
Local type / projection: G ↾ p is the projection of G to participant p, syntactically translating each global statement into the corresponding send/receive/select/branch from p’s perspective.
Coherence (well-formedness): a global type is well-formed iff every choice point is observed by every relevant participant — the multiparty analogue of the connectedness condition in Structured Communication-Centred Programming for Web Services.
Asynchronous π-calculus substrate: processes communicate over typed session channels with non-blocking send and FIFO queues; each session is opened with a fresh name and closed structurally.
Subject reduction: well-typedness is preserved under reduction.
Communication safety: no well-typed system ever sends a value whose type the receiver does not expect.
Session fidelity / progress: the runtime trace of a well-typed system is a refinement of the projected local types, and well-typed systems whose buffers are empty cannot deadlock.
Type-driven engineering payoff: type-check the global protocol once, get communication-safety guarantees for every role for free.

Connections

Conceptual Contribution

Claim: Multiparty distributed communication is best disciplined by a single global type describing the joint protocol of all participants, from which per-participant local types are derived by mechanical projection; well-typedness of the global type plus a coherence condition ensuring choice points are observed by all relevant parties is sufficient to guarantee that every projected process is communication-safe, deadlock-free, and faithful to the global protocol.
Mechanism: Define global types as a calculus over N ≥ 2 participants with sending, branching, recursion, parallel composition; define local types as session types with send/receive/select/branch; define a syntactic projection G ↾ p from global to local types per participant; type processes (extended asynchronous π-calculus with FIFO message buffers) against the projected local types; prove subject reduction (well-typedness preserved under reduction), communication safety (no type-mismatched messages), and progress (well-typed systems with empty buffers do not deadlock).
Concepts introduced/used: Session Types, multiparty session types, global type, local type, projection, coherence, subject reduction, asynchronous π-calculus, communication safety, session fidelity
Stance: foundational / formal-semantic
Relates to: Companion to Structured Communication-Centred Programming for Web Services (Carbone-Honda-Yoshida ESOP 2007 / TOPLAS 2012) — the two papers together establish the modern global types → local types → processes pipeline that all subsequent choreographic-programming and multiparty session-types work inherits. Without the multiparty extension here, the binary session-type substrate of Carbone-Honda-Yoshida 2007 cannot scale to the N-participant choreographies that real protocols need. Underwrites the contemporary textbook Introduction to Choreographies (Montesi 2023). Provides the type-system substrate that On the Monitorability of Session Types (Bartolo Burlò et al. ECOOP 2021) lifts into a runtime-monitoring theory, and that Pact - A Choreographic Language for Agentic Ecosystems adds game-theoretic operators on top of. The structural counterpart in the agent-communication tradition is Commitment Machines - Yolum and Singh / Flexible Protocol Specification and Execution: both lineages (multiparty session types ↔ Yolum-Singh commitment protocols) take a globally-specified N-participant protocol, project to per-role views, and prove the projection preserves a key correctness property (communication safety here, commitment discharge there). The π-calculus substrate descends from Communicating Sequential Processes (Hoare 1978) and Milner’s π-calculus.

Tags

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

FIPA-ACL Specifications

Reference: Foundation for Intelligent Physical Agents (2002). FIPA ACL Message Structure Specification (FIPA00061) and FIPA Communicative Act Library Specification (FIPA00037). Geneva, December 2002. (FIPA was absorbed into the IEEE Computer Society in 2005; specifications remain the canonical reference.) FIPA00061 (Message Structure) · FIPA00037 (Communicative Act Library) · FIPA00067 (Agent Message Transport) · IEEE FIPA standards committee

Summary

The FIPA-ACL specifications are the standards-track distillation of the late-1990s mentalistic ACL programme: the wire format and semantics that “ended up shipping” as the canonical example of an industry-grade agent communication language. The suite splits into three documents that matter for ACL design. FIPA00061 specifies the message structure — the surface syntax of an ACL message as a parameterised performative envelope with :sender, :receiver, :content, :language, :ontology, :protocol, :conversation-id, :reply-with, :in-reply-to, :reply-by, and a small set of related parameters. FIPA00037 specifies the communicative act library — twenty-two performatives (accept-proposal, agree, cancel, cfp, confirm, disconfirm, failure, inform, inform-if, inform-ref, not-understood, propagate, propose, proxy, query-if, query-ref, refuse, reject-proposal, request, request-when, request-whenever, subscribe) — each given by feasibility precondition (FP) and rational effect (RE) expressed in the FIPA Semantic Language (SL) over beliefs, intentions, and uncertainty. FIPA00067 specifies the message transport (HTTP, IIOP, WAP carriers; envelope and routing).

Two features make FIPA-ACL the canonical reference point — and the canonical negative example — for ACL semantics work. First, the direct lineage from Cohen and Levesque: the FP/RE structure of FIPA00037 is a streamlined adaptation of Cohen and Levesque 1995. The semantics of inform(p) is, modulo notation, exactly the Cohen–Levesque definition: the sender believes p, believes the receiver does not know p, and intends the receiver to come to believe p. The semantics of request mirrors attempt over a hearer action. Second, the unverifiability problem: precisely because the semantics is given in terms of sender and receiver mental states, no external observer can determine whether a message is FIPA-conformant. A platform that ships inform(p) in violation of its feasibility preconditions (e.g. the sender does not believe p, i.e. is lying) is indistinguishable on the wire from a platform that ships a conformant inform. This is the deficiency Singh 1998 names, Wooldridge formalises, and the commitment-based semantics tradition fixes.

For this vault, FIPA-ACL is the engineered artefact against which the public-semantics critique runs. The spec is well-engineered as a message format — the envelope, the protocol-id mechanism, the ontology / language slots are all sound — and the wire format itself has aged well. What has not aged well is the semantics by mental-state precondition: it is unverifiable, hostile to heterogeneous deployment, and incompatible with the public-semantics / commitment-based programme that CBCL inherits. The right reading is: keep the engineering, replace the semantics.

Key Ideas

Three-part suite: FIPA00061 (message structure), FIPA00037 (communicative act library), FIPA00067 (message transport).
Message structure: :sender, :receiver, :content, :language, :ontology, :protocol, :conversation-id, :reply-with, :in-reply-to, :reply-by, :performative. Standard envelope; the :content slot carries an arbitrary content-language expression interpreted by the :ontology.
Twenty-two performatives: from accept-proposal through subscribe, organised loosely into Searlean families (assertives, directives, commissives, declaratives). The set is small enough to remember and rich enough to cover most multi-agent interaction patterns.
Semantic Language (SL): FIPA’s formal language for FP/RE definitions; a modal logic over belief, uncertainty, intention, and action, descended from Cohen and Levesque.
Feasibility precondition / rational effect: each performative is defined by an FP (what must hold for the agent to perform the act in good faith) and an RE (what the agent intends to bring about). Both involve nested beliefs and intentions of sender and receiver.
Interaction protocols: FIPA also standardises a small set of interaction protocols (FIPA-Request, FIPA-Query, FIPA-ContractNet, FIPA-IteratedContractNet, FIPA-EnglishAuction, FIPA-DutchAuction, FIPA-Brokering, FIPA-Recruiting, FIPA-Subscribe, FIPA-Propose) — finite state machines over performatives that script common conversational patterns.
Unverifiability is intrinsic: the FP/RE conditions are stated over mental states; no external observer can check conformance without inspecting agent internals — a known design cost and the central target of the social-agency critique.

Connections

Conceptual Contribution

Claim: A standardised ACL can be built from a small set of performatives, each given by mental-state preconditions and intended effects in a modal logic, embedded in a standardised message envelope, with a standard library of interaction protocols. The result is the canonical industry ACL.
Mechanism: Three coordinated specs. FIPA00061 fixes the wire format (envelope parameters and message routing). FIPA00037 fixes the performative semantics in SL, with each of twenty-two performatives given by FP and RE in terms of belief, uncertainty, and intention nested over sender and receiver. FIPA00067 specifies the message transport. A small library of interaction protocols (FIPA-Request, FIPA-ContractNet, etc.) gives canonical conversational patterns as finite state machines over performatives.
Concepts introduced/used: FIPA Performative, Semantic Language (FIPA SL), Feasibility Precondition, Rational Effect, FIPA Interaction Protocol, ContractNet, ACL Message Envelope, Conversation ID.
Stance: standards specification suite / industry deliverable.
Relates to: Direct standardisation of Cohen and Levesque 1995 — the FIPA00037 semantics is essentially that paper’s framework with editorial smoothing. As the canonical engineering artefact of mentalistic ACL semantics, FIPA-ACL is the negative example for Singh 1998, Wooldridge, Yolum & Singh, Fornara & Colombetti, and the public-semantics tradition generally. CBCL reuses the engineering of FIPA-ACL (typed performative envelope, conversation-id, ontology slot, protocol-id) while replacing the semantics with publicly verifiable commitment-based meaning. The modern LLM-agent protocol generation (Model Context Protocol, Agent-to-Agent Protocol, LACP) has retreated from FIPA’s level of semantic ambition; the open question is whether that retreat will repeat the mentalistic mistake under a new guise (sycophantic JSON tool-calls) or learn from the FIPA experience.

Agents and Artifacts

Agents and Artifacts (A&A)

Meta-model treating the agent environment as first-class artefacts agents interact with, implemented in JaCaMo / CArtAgO.

In this vault

An Interaction-oriented Agent Framework for Open Environments

An Interaction-oriented Agent Framework for Open Environments (Mercurio)

Reference: Baldoni, Baroglio, Bergenti, Marengo, Mascardi, Patti, Ricci, Santi (2011). AIIA 2011 (Italian AI Association)*. Source file: cbcl-ref/AI_IA2011.pdf. URL

Summary

The authors propose Mercurio, an agent-programming framework for open multi-agent systems that unifies direct (speech-act) and indirect (environment-mediated) communication under a single social/observational semantics based on commitments. Mercurio has three levels — specification (constitutive and regulative rules over a domain model), programming abstractions (Agents and Artifacts in the A&A meta-model), and infrastructure (built on JaCaMo integrating Jason, CArtAgO, and MOISE).

Commitment-based protocols give a public, verifiable meaning to actions (replacing mentalistic ACL semantics); constitutive rules define what counts as what, while regulative rules impose temporal constraints on the social state. Artifacts reify interaction patterns and the social state itself, enabling the environment to monitor and detect violations. The framework thus conjugates MAS flexibility with software-engineering modularity and compositionality, targeting e-government, cross-business, and service-oriented applications.

Key Ideas

Commitment-based social semantics replaces mentalistic ACL semantics.
Three levels: specification, programming abstractions, infrastructure.
Separation of constitutive and regulative rules.
Artifacts (A&A / CArtAgO) as first-class environment entities.
JaCaMo stack (Jason + CArtAgO + MOISE) as reference infrastructure.

Connections

Conceptual Contribution

Claim: Open multi-agent systems need a single, publicly verifiable interaction semantics that unifies direct (speech-act) and indirect (environment-mediated) communication; commitments plus Agents-and-Artifacts supply it and can be layered onto an existing AOP stack.
Mechanism: Mercurio stratifies into three levels. (1) Specification: a domain model plus constitutive rules (“what counts as what”) and regulative rules (temporal constraints on the social state). (2) Programming abstractions: the A&A meta-model (agents + artifacts) where artifacts reify interaction patterns and the social state itself. (3) Infrastructure: the JaCaMo stack (Jason + CArtAgO + MOISE) runs the above so violations are environment-detectable and the social state is inspectable.
Concepts introduced/used: Mercurio Framework, Commitment-Based Protocol, Constitutive Rules, Regulative Rules, Agents and Artifacts, JaCaMo, Jason, CArtAgO, MOISE, Social State
Stance: engineering
Relates to: Concretely instantiates the social-semantic programme of Agent Communication Languages - Rethinking the Principles and the open-issue agenda of Trends in Agent Communication Language and The State of the Art in Agent Communication Languages; its environment-reified interaction complements the self-organisation of A Composite Self-organisation Mechanism in an Agent Network.

Tags

AgentSpeak

Rao’s (1996) operational BDI agent programming language: an agent is a triple of belief base (Prolog facts), plan library (event-triggered procedures), and intention stack (plans-in-execution). The interpreter cycles through perceive → event-generate → plan-select → execute. Eight-rule SOS-style operational semantics fits on a page. Made practically dominant through Jason (Bordini-Hübner-Wooldridge 2007), the most-deployed BDI platform in academic MAS research.