Task scripts, use cases and scenarios in object oriented analysis

This paper presents an approach to object oriented requirements engineering and business process re-engineering with a number of advantages over the widely used use case technique. It points out some problems with the use case approach and explains the origins of the idea of task scripts. It compares the two approaches and defines their interrelatedness. The paper sets out to improve and clarify the terminology in use with respect to concepts such as use cases, scenarios and scripts and, in doing so, offers a generification of the use case concept: the task script. This clarification may be viewed as an object oriented 'analysis pattern': the syllogism pattern. The concepts are introduced in the context of SOMA: a practical approach to business process modelling based on the object oriented metaphor of message passing. In this approach, messages represent semiotic acts that are expressions of contractual relationships between stakeholders in a business process and the artefacts used by them. It is also indicated how the business process model can be converted into a potentially implementable business object model and the two models linked seamlessly together. Finally, task scripts are compared with Constantine's 'essential use cases'.