Service-oriented computing (SOC) is emerging as a promising paradigm for integrating software applications within and across organizational boundaries. In this paradigm, independently developed and operated applications are exposed as (Web) services which are then interconnected using a stack of Web-based standards including SOAP, WSDL, UDDI, WS-Security, etc. While the technology for developing basic services and interconnecting them on a point-to-point basis has attained a certain level of maturity and adoption, there are still many open challenges when it comes to managing interactions with complex services or managing interactions involving large numbers of services.