Developing bounded FIPA-style conversations with JADE

Source boundary

Bellifemine, Caire, and Greenwood’s Developing Multi-Agent Systems with JADE (Wiley, 2007; DOI 10.1002/9780470058411) is the topic source. The accessible Wiley record establishes bibliographic identity; the book body was not accessed for this draft. Current implementation guidance is from official JADE 4.6.0 API documentation and the official Programmer’s and LEAP User Guides, accessed 2026-09-24. Treat every deployment timeout, retry, score, persistence choice, and external effect as an application policy, not as a property supplied by FIPA or JADE.

Choose a conversation before choosing a class

flowchart TD
  A[Describe the intended result and evidence] --> B{Many candidates offer a bounded task?}
  B -->|yes| C[CFP: freeze eligibility, reply-by, proposal schema, selection rule]
  B -->|no| D{One known party is asked to act?}
  D -->|yes| E[REQUEST: define refusal, completion evidence, and deadline]
  D -->|no| F{Ongoing observations wanted?}
  F -->|yes| G[SUBSCRIBE: define update scope, cancellation, and stale-data handling]
  F -->|no| H[Use an application-defined exchange and document its semantics]
  C --> I[Bind conversation ID, ontology/content language, and correlation]
  E --> I
  G --> I

A performative classifies a message in a conversation. It does not authenticate a sender, prove a proposition, transfer a capability, or make an external action happen. Admit identity, validate content, and authorize effects independently.

A worked local policy: selecting a document converter

The following is an application policy, not a FIPA or JADE default. A requester sends a CFP with immutable conversationId, input digest, allowed output format, reply-by time, and evaluation fields. It records every PROPOSE and REFUSE received before the reply-by time, selects at most one proposal with a declared local comparator, sends ACCEPT-PROPOSAL to that proposal and REJECT-PROPOSAL to the other recorded proposals. The selected party later emits either INFORM containing an output reference or FAILURE containing an attempted-stage record. The requester checks the output independently before using it.

sequenceDiagram
  participant R as requester
  participant A as candidateA
  participant B as candidateB
  R->>A: CFP request digest reply-by and proposal schema
  R->>B: CFP request digest reply-by and proposal schema
  A-->>R: proposal with declared terms
  B-->>R: refusal with reason
  R->>A: accept proposal
  Note over R,B: B refused, so it receives no rejection
  A-->>R: later report or reported failure
  R->>R: independently validate output and record disposition

A Java-like sketch preserves the source bundle’s separation between proposal collection, local evaluation, and completion. It is deliberately not a copy-paste release contract; verify constructors, callbacks, and templates against the selected JADE release.

// Illustrative Java-like behavior sketch; local policy owns time and ranking.
void onCfpClosed(List<ACLMessage> replies, String conversationId) {
  List<ACLMessage> proposals = replies.stream()
      .filter(m -> m.getPerformative() == ACLMessage.PROPOSE)
      .filter(m -> conversationId.equals(m.getConversationId()))
      .toList();
  Optional<ACLMessage> chosen = chooseUnderLocalPolicy(proposals);
  for (ACLMessage p : proposals) send(replyTo(p, p == chosen.orElse(null)
      ? ACLMessage.ACCEPT_PROPOSAL : ACLMessage.REJECT_PROPOSAL));
  if (chosen.isEmpty()) recordNoSelection(conversationId, replies);
}

Content and behavior boundaries

Use an ontology/content-language agreement when independently built parties must share a meaning for fields such as inputDigest, format, or declaredTerms. A matching JSON field name or a successful Java decode is only syntactic interoperability. Version each schema, reject messages outside the agreed version, and retain the original bytes/digest so the application can explain what it accepted.

JADE behavior composition remains useful as a local implementation technique: a short setup behavior may register a service description; a conversation behavior may wait for matching messages; a final behavior may record a disposition. Do not infer that a Directory Facilitator result proves suitability, availability, authorization, or delivery. It is discovery input.

Within one agent, JADE schedules ready behaviours cooperatively and non-preemptively: action() returns to yield, and a waiting behaviour calls block() then returns. Persist the phase and correlation data in fields or a DataStore; a Java call stack is not preserved across scheduler turns. Use SequentialBehaviour for ordered local steps, ParallelBehaviour with WHEN_ALL or WHEN_ANY only for completion semantics, and FSMBehaviour when refusal, no-selection, report, and validation need explicit transitions. None turns remote work into CPU-parallel work.

For a dynamic candidate list, DFService.search, register, modify, and deregister are convenient but block the caller until completion or exception. Keep that work out of a latency-sensitive behaviour, or use the asynchronous DF request/subscription path (AchieveREInitiator or SubscriptionInitiator) with a documented update policy. A MessageTemplate selects queued ACL messages by header predicates; include conversation-id, protocol, performative, and a reply-with/in-reply-to pair as appropriate, then validate sender role and content separately.

Failure dispositions

Observation	Conversation disposition	What remains unproved
REFUSE before selection	Candidate declined this request	Cause, future availability, and truth of a supplied reason
no response by the declared reply-by	Reply missing for this local window	Network state or remote execution state
FAILURE after acceptance	Candidate reports an unsuccessful attempt	The report’s accuracy and any external rollback
INFORM with output reference	Candidate reports completion	Output integrity, fitness, and any downstream effect

Do not label an absent response “Byzantine,” choose arbitrary global thresholds, promise persistent delivery, or automatically blacklist/retry. Those are separate threat-model and operations decisions.

Quality gates

• The chosen protocol has a written message grammar, correlation identifier, and local terminal condition.
• CFP policy freezes who may be considered, reply-by interpretation, proposal fields, and selection comparator before proposals are evaluated.
• Request, refusal, missing-response, reported failure, and reported completion have distinct recorded dispositions.
• Content validation and independently authorized external effects occur outside performative handling.
• Any JADE API use is checked against a named release’s official documentation.
• Time, retries, caches, queueing, and discovery behavior are measured local policies with explicit assumptions.

Read next

• Conversation contract and JADE mapping
• Behavior composition and message correlation
• Source access and implementation boundary
• CFP lifecycle diagram
• Implementation boundary diagram

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