UML Use Case Diagrams are a first step towards the definition of system requirements, however, they do not provide enough information for many purposes. UML Activity Diagrams (AD) and Use Case Maps (UCM) provide such information in a quite comprehensive manner. The first part of my talk deals with a "Core Scenario Model" (CSM) which was developed to capture the common semantics of AD and UCM, as well as performance-related information.

The CSM can be easily translated into Petri nets, and it is also related to the BPEL notation of Web Services, which could be taken as an implementation environment. In the second part of my talk, I will discuss how one can derive an application protocol from system requirements Given in the form of such notations together with a distributed system architecture that identifies a certain number of system components. The resulting protocol will define the behavior of all the system components in such a manner as to ensure the given requirements. This problem is relatively easy to solve if each choice between alternative actions in the requirements can be performed by one of the components alone, however, it becomes quite complex if information from several components must be considered for doing such choices. We also discuss how the concept of (distributed) transactions, in the sense of databases, can be integrated into the description of requirements.