Dependency Charts as a Means to Model Inter-Scenario Dependencies

Scenarios/use cases have gained wide-spread use over the last couple of years. In software engineering they are mainly used to capture requirements and specify a system. Many software engineering approaches, most notably the UML (Unified Modeling Language [RJB99]), use some notion of scenario to support requirements elicitation and to provide a means for improved communication between software engineers, customers and users, and for enhanced user integration in the software development process. Yet prominent and renowned approaches like the UML lack a concept for modeling dependencies and relations between scenarios and offer only little support for the description and management of scenarios and of inter-scenario relationships. However, dependencies between scenarios are common, in fact dependencies between scenarios occur in any software development project of reasonable size. The existence of dependencies among scenarios needs to be perceived, acknowledged and accepted, they have to be captured and modeled to fully specify and better understand the system, and their impact on system modeling, on design, implementation and on testing needs to be recognized. In this paper we argue that dependencies among scenarios play too important a role in the software development process to omit them from system models and not to consciously consider them in analysis, design and testing. Therefore, we introduce a new kind of chart and a notation to model dependencies among scenarios. We discuss briefly the reasons why a new kind of chart is needed. An example of a dependency chart is presented.