From SSKE

Web services are self-contained software services that can be accessed using simple protocols over a network. They can also be described using standard mechanisms, and these descriptions can be published and located using standard registries. Web services can perform a wide variety of tasks, ranging from simple request-reply tasks to full business process interactions.

Web services provides a technology foundation for implementing an SOA. A major focus of this technology is interoperability. The functional building blocks must be accessible over standard Internet protocols. Internet protocols are independent of platforms and programming languages, which ensures that high levels of interoperability are possible.