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Selection of Provider

The result of the matching between the request and the advertisements will result in a number of matches among which the requester will have to select the provider it wants to use. In general there is no hard and fast rule for the selection of the provider, and it soon turns out to be a domain specific decision.

The simplest thing is to select the provider with the highest score among the Web Services reported by the Registry. A more general approach could be based on decision theoretic reasoning, in which the requester selects the provider that maximizes some utility function, but, in practice, it is unlikely that Web Services will make use of an explicit utility model that they can leverage on.

Other types of information that are not contained neither in the request nor in the advertisement such as the credit history of a provider, or the amount of work the requester estimates to do in order to satisfy all the inputs and preconditions expected by the provider and in general the likelihood that the requester can gather all the input information and achieve all the preconditions expected by the provider.

The strategies proposed above assume that the requester will select only one provider to interact with. This decision may be extremely risky and inefficient in the world of Web Services. One nice part of Web Services is that they run on the same time on different machines implementing actual parallelism. As a consequence, the requester may attempt to interact with multiple providers in the same time; with the advantage that by delaying the selection of the provider it reduces the risks of an early decision. Of course, the problem of this strategy is that the requester may commit to buy the same service from multiple providers, incurring in additional costs at no gain [5]. Therefore, this strategy can be followed only when the requester is aware of the place in the transaction where it commits to buy, at which point the requester may commit on a provider. For example, a requester interested in buying books may try to interact with more than one book selling Web Service in the attempt to find the cheaper one. This will be a good strategy as long as the requester selects from which Web Service to buy before it commits to buy the same book from all the providers.

next up previous
Next: Interaction with Provider Up: Composition Cycle Previous: Location of Providers
Massimo Paolucci 2003-02-28