Selective Querying using Value of Changed Information for Adapting Hierarchical Web Service Compositions

Environments in which Web service compositions (WSC) operate are often dynamic. We address the problem of which service to query for up-to-date information in order to adapt a hierarchical WSC, given that queries are not free. Previously, the value of changed information (VOC) has been proposed to select those services for querying whose revised non-functional information is expected to bring about the most change in the composition. VOC requires a distribution over the possible values of volatile parameters of the WSs. In this paper, we present an approach for utilizing VOC in the context of a WSC composed of WSs and lower level WSCs, which induces a natural hierarchy over the composition. Because parameters of composite WSs are not directly available, we aggregate these from parameters of component WSs and derive a distribution over the possible parameter values from the distributions for the WSs.