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Next: JIM Up: Conversation Protocols Previous: Compatibility Semantics

Conversation Protocol Negotiation


In Section 3.3 we introduced the several attributes of a CP instance that have to be fixed before the conversation between the speakers becomes fully instantiated, and subsequently started. The value of each one of these attributes has to be mutually agreed by the speakers in order to guarantee conversation soundness. For this purpose, interagents have been provided with the capability of negotiating such values by means of the so-called Handshake phase, following the directions of their customers. During this process, the initial connection between the originator and the helper is established, and next the originator conveys its multi-attribute proposal (the set of attributes' values) to the helper. Then, we distinguish two models of negotiation based on the helper's response: one-step and two-step negotiation.

In one-step negotiation the helper either automatically accepts or refuses the originator's proposal. The following sequence depicts a typical exchange for this model of negotiation, where q values indicate the degree of preference over each proposal.

 originator: START

CP/DBP; id=21; polarity=+; leader=me; q=0.7

CP/DBP; id=21; polarity=-; leader=you; q=0.3

helper: OK

CP/DBP; id=21; polarity=+; leader=me

In this example the helper accepts the second proposal from the originator.

In two-step negotiation, instead of directly accepting or refusing the originator proposal, the helper can reply with a a list of counterproposals ranked according to its own preferences. Then, the originator can either accept one of these proposals or cancel the process.

 originator: START

CP/DBP; id=22; polarity=+; leader=me; timeout=500; q=0.7

CP/DBP; id=22; polarity=-; leader=you; timeout=1000; q=0.3

helper: NOT

CP/DBP; id=22; polarity=-; leader=me; timeout=200; q=0.4

CP/DBP; id=22; polarity=+; leader=you; timeout=200; q= 0.6

originator: OK

CP/DBP; id=22; polarity=+; leader=you; timeout=200

In this example the helper refuses the proposals of the originator, who finally accepts the first helper's counterproposal.

It should be noted here that the concrete conversation protocol to be instantiated can be negotiated too. For this purpose, we have introduced the CP type (f.i. the CP/DBP for the downward bidding protocol), analogously to MIME content types (text/html, image/gif, etc.). On the other hand, it is nonsense to negotiate certain attributes for some CPs. For instance, the polarity of the CP to be employed by an auctioneer attempting to open a DBP round is unnegotiable since the auctioneer cannot play the role of a buyer and vice versa.

next up previous
Next: JIM Up: Conversation Protocols Previous: Compatibility Semantics

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Wed Mar 10 11:44:57 MET 1999