A central element of emerging Service Oriented Architectures (SOA) is the ability to develop new applications by composing enterprise functionality encapsulated in the form of services ? whether within a given organization or across multiple ones. Semantic service annotations, including annotations of both functional and non-functional attributes, offer the prospect of facilitating this process and of producing higher quality solutions. A significant body of work in this area has aimed to fully automate this process, while assuming that all services already have rich and accurate annotations, In this article, we argue that this assumption is often unrealistic. Instead, we describe a mixed initiative framework for semantic web service discovery and composition that aims at flexibly interleaving human decision making and automated functionality in environments where annotations may be incomplete and even inconsistent. An initial version of this framework has been implemented in SAP?s Guided Procedures, a key element of SAP?s Enterperise Service Architecture (ESA).