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Negotiating

The way Agents communicate is fundamentally different to the object-oriented paradigm.

Instead of calling Agents directly, communication between Agents is more akin to human language exchanges such as in bartering scenarios.

Quote

Objects do it for free; agents do it because they want to.

FIPA (Foundation for Intelligent Physical Agents) is a well known standard for agent negotiation. In the OEF, communication follows a minimal subset of the FIPA language. For instance:

  • Buying Agent b requests a resource r from Selling Agent s by sending a call for proposal cfp(r).
  • Selling Agent s replies by sending a proposal to b with propose(r, p), where r is the resource requested and p is the seller’s asking price.

Specifically, the negotiation system has the following components:

  1. A set of speech-acts where each item may also be called a locution:

    {cfp(r), propose(r,p), accept(), decline()}
    
  2. A reply structure, where each locution is only a valid reply to some other locutions. This is denoted in the following table:

    Locution Could reply to
    cfp(r)
    propose(r,p) cfp(r) or propose(r,p)
    accept() propose(r,p)
    decline() cfp(r)
  3. A set of moves where each move has the following format:

    id sender speech-act target

    Where id is the identity of the move in a dialogue, sender is the agent who sends this move, speech-act is the actual content of the move (i.e. its locution) and target is the id of the move this move is replying to.

A dialogue is then just a sequence of moves, where the first move’s target is 0 (the first move is not replying to any other move in the dialogue).

An example of a simple negotiation between a buying Agent b and selling Agent s over the resource r is as follows:

id Agent locution target
1 b cfp(r) 0
2 s propose(r, 20) 1
3 b propose(r, 10) 2
4 s propose(r, 15) 3
5 b accept() 4

Note the following simple protocol rules:

  • The negotiation dialogues always start with a cfp(r) move.
  • A dialogue terminates when an accept() or decline() is sent.
  • Agents take turns to send moves in the dialogue. In other words, one agent could only send one move in its turn and has to wait for a response from the other agent before being able to send another move.
  • Agents can only reply to the move of the other agent, and not their own.

Current implementation

In the current version of the OEF SDK, callbacks tell Agents which step of the FIPA protocol has occurred.

View of the FIPA negotiation sequence between agents.

Note

All FIPA messages are implemented as byte streams or dictionary types.

For example, Agent Alice sends a sendCFP (call for proposal) message containing the public key and query to Agent Bob via the OEF which forwards an onCFP.

Agent Bob receives the onCFP event and replies with a sendPropose containing a list of proposals.

Bob's sendPropose has the same identifier that came with the onCFP. This means that Alice can refer back to the CFP when she gets the onPropose event.

onACK and onDeal finalise the communication (more).

Finally, Agent Alice receives the byte payload from Agent Bob on sendMessage.

Every message contains the following:

  • dialogue id: the identifier of the dialogue in which the message is sent.
  • destination: the agent identifier to whom the message is sent.
  • message id: the message identifier for the dialogue.
  • target: the identifier of the message to whom this message is answering.