In this article we review the metaphor of service-oriented architecture for enterprise computing. In typical definitions service-oriented architecture appears as a single message and a consistent roadmap for building flexible software system landscapes. But it is not. Different communities have elaborated different SOA (service-oriented architecture) concepts to address different problem areas, i.e., enterprise application integration, business-to-business, business process management, and software productizing. If software architects and software managers are aware of these strands of SOA when talking about SOA in their projects they can avoid misunderstandings and detours better. This article contributes a clarification of the different strands of SOA concepts and technologies and their mutual dependencies and identifies particular SOA concepts as instances of more general software engineering principles.