and Testing them for Minimum Quality
GMD German National Research Center for Information Technology
Scenarios have increasingly been used as a source of domain knowledge enabling analysts and designers to deepen their understanding of the users'/customer's requirements ( Weidenhaupt et al., 1998). This paper is aimed at concisely describing the process of scenario acquisition, the extraction of requirements from scenarios, the validation of both scenarios and requirements and a test for compliance with an international usability standard (ISO 9241-10), thereby achieving validated minimum requirements as early as possible in the design process.
The focus of this paper is an analysis of non-functional and usability requirements elicited from the context of product use. Our approach can be seen as an amendment to an otherwise accomplished functional analysis, for instance, a use-case analysis. The knowledge to be captured for requirements analysis is represented in two types of scenarios, context and use scenarios, the acquisition of which being conducted iteratively in a two-steps process.
Context scenario is defined as a narrative and episodical description of the user's tasks conducted in his current context. The product to come is not yet considered in this type of scenario, however, its envisaged usage is described as far as the prospective user can give an idea of it. Drawing on concepts of Carroll ( 1994, 1995), we want to define use scenario as a narrative and task-related description of the actual use of a product (or prototype). The distinction between both kinds of scenarios goes along with an acquisition of knowledge in two steps, first the domain knowledge, then the knowledge of how to use a system. The elicited knowledge serves as a basis for deriving usability requirements, first the context related then the use related ones. The analyst thus specifies requirements, which can be easily validated by the user, since each requirement is linked to a statement in the scenario. Usability standards, in particular ISO 9241-10, serve as an additional source to transform the elicited context and use requirements in terms of minimum usability requirements. The analyst thus tests the requirements for compliance with usability standards.
Theoretical and methodical reasons have been published arguing that the analysis of domain-specific requirements and usability design (i.e. prototyping) are inevitably intertwined ( Dzida and Freitag, 1998). For this reason, we regard