Stateful SOA-conformant Services as Building Blocks for Interactive Software Systems

Services implemented through information and communication technology need to provide value for customers, with whom they usually have non-trivial interaction. However, user interface and (Web) service specifications are often disconnected. The most widely used Web services are stateless, hence only trivial user interaction with one-step input and output can be embedded in such a service. Remembering the state is a prerequisite for implementing nontrivial user interaction with a service. We present new stateful SOA-conformant services as building blocks for interactive software systems. This new kind of service has a unified high-level protocol both for (non-trivial) user interaction with a machine and for machine-machine communication. Services with the same protocol can substitute each other (also dynamically at runtime), whether they are machine or user services. Using such services as building blocks, interactive software systems can be composed, also recursively. As a matter of fact, from such service specifications (graphical) user interfaces for non-trivial interaction can be automatically generated.