As the Service Oriented Architecture (SOA) principles have gained importance, an emerging need has appeared for methodologies to locate desired services that provide access to their capability descriptions. These services must typically be assembled Into short-term service collections that, together with code execution services, are combined into a meta-application to perform a particular task. To address metadata requirements of these problems, we introduce XML Metadata Services to manage both stateless and stateful (transient) metadata. We leverage the two widely used web service standards: Universal Description, Discovery, and Integration (UDDI) and Web Services Context (WS-Context) in our design. We describe our approach and experiences when designing "semantics" for XML Metadata Services. We report results from a prototype of the system that is applied to mobile environment for optimizing Web Service communications. © 2006 IEEE.