Process models

'Process modeling has been a mainstay of software development for decades and will continue to as long as we need to build business systems'

Process models allow us to describe the often complicated flow of logic within a system. Process models typically depict sources of information outside the scope of your system, which are called actors in use case models and the way they interact with the system. Process models also show, albeit at a high level sometimes, how information is processed by the system to support these interaction, depicting process/activities and the information flowing between them. Process models can be used to analyze an existing system, to analyze an existing business process, to design a new business process, or to design a new system'

(Scott W. Ambler - 'The object primer - agile model-driven development with UML 2.0')