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IADIS International Conference WWW/Internet 2010rank all possible combinations and to come to an agreement on one of them. Raising the amount ofparameters and parameter values raises the possibilities and the amount of proposals becomes unmanageable.An example: If 5 parameters and 3 alternatives per parameter are given to negotiate, already 3 5 = 243proposals are possible. For such a multi-criteria decision problem a decision matrix can be used to find thebest choice. As already mentioned these decision matrices can differ for the negotiation partners. In thispaper we present an approach to specify the preferences on service quality parameters or other negotiableparameters and introduce a component which, based on the given decision matrixes, creates a nearly optimalproposal for a contract, which can be finished by the partners with a chosen protocol. The advantage of thiscooperative approach is to simplify the negotiation process for service consumers and providers byintroducing a way to model their preferences.Section 2 gives a brief architecture overview, followed by the description of the representation model forthe decision matrix. The process of finding the proposal is explained in Section 4 and the article finishes witha conclusion and outlook to future work.2. ARCHITECTURE AND NEGOTIATION PROTOCOLFigure 1 gives an overview of the architecture of the negotiation module. It provides two web serviceinterfaces for the negotiation process. One is to initiate the calculation process and the other is to poll theresult.Figure 1. Architecture of the negotiation moduleWith the initiation call a negotiation initiator introduces their constraints (preferences for differentparameters) for a specific service and receives an identifier for polling the result afterwards. The negotiationmodule will fetch the constraints for the corresponding service provider from a central component, the SLAmanager, which administrates the SLA templates. For a detailed view on an SLA-based infrastructure see[Winkler09]. The two given constraint sets are matched by the calculation module and the best proposal iscalculated. The initiator polls the proposal and converts it to their favored SLA format. In WSAG protocolfor example the proposal will be sent by the wsag:CreateAgreement(AgreementOffer) operation.3. REPRESENTATION OF USER PREFERENCESIn this section we present our model to represent the negotiations partners’ needs. For multi-criteria decisionproblems, a decision matrix can be used to find the best combination for several values of parameters.We define all negotiable parameters as p 1 ,...,p n . For each parameter p i a meta-information tuple Ip i ={name, metric, guarantor, kov, tov, info} and a set of values v pi = {v 1 ,..,v k } is given. The information tupleidentifies this parameter and gives all needed information. Name and metric are self-evident, the guarantormeans the partner who is responsible to keep the specific value that may be the consumer or the provider.KindOfValue (kov) indicates whether the values v pi are discrete or continuous values. If they are continuousvalues, the value set consists of only two values, the maximum and the minimum. An example: for theparameter “responseTime” normally a range will be defined (continuous) while for the parameter283