What's in an agreement? An analysis and an extension of WS-agreement

Non-functional properties of services and service compositions are of paramount importance for the success of web services. The negotiation of non-functional properties between web service provider and consumer can be agreed a priori by specifying an agreement. WS-Agreement is a recently proposed and emerging protocol for the specification of agreements in the context of web services. Though, WS-Agreement only specifies the XML syntax and the intended meaning of each tag, which naturally leads to posing the question of What's in an Agreement? We answer this question by providing a formal definition of an agreement and analyzing the possible evolution of agreements and their terms. From our analysis we identify ways in which to make an agreement more robust and long lived by proposing two extensions to the specification and supporting environment.