A More Expressive Softgoal Conceptualization for Quality Requirements Analysis

Initial software quality requirements tend to be imprecise, subjective, idealistic, and context-specific. An extended characterization of the common Softgoal concept is proposed for representing and reasoning about such requirements during the early stages of the requirements engineering process. The types of information often implicitly contained in a Softgoal instance are highlighted to allow richer requirements to be obtained. On the basis of the revisited conceptual foundations, guidelines are suggested as to the techniques that need to be present in requirements modeling approaches that aim to employ the given Softgoal conceptualization. 1 Dealing with Software Quality Requirements Ensuring the quality of software has become a major issue in software engineering research and practice since the 1970s [5]. As increasingly complex software plays a critical role in business, comprehensive and precise methods and tools are needed to create software products and services that are safe, dependable, and efficient [26]. Software quality is defined by the International Organization for Standardization [12] as the totality of features and characteristics of a software product that bear on its ability to satisfy stated or implied needs. Ensuring the quality of software therefore amounts to making sure that software behavior is in line with stated and implied needs. It is widely acknowledged that quality needs to be taken into account early in the software development process [8,30,19]. Quality requires specifying stated and implied needs. Approaches focusing on ensuring quality during the development process by guiding functional requirements specification decisions by quality considerations, so that the latter justify the former, are termed processoriented. In contrast, product-oriented approaches (e.g., [11,13]) evaluate the quality of already developed software products, and are particularly relevant for, e.g., component selection [2]. D.W. Embley, A. Olivé, and S. Ram (Eds.): ER 2006, LNCS 4215, pp. 281–295, 2006. c © Springer-Verlag Berlin Heidelberg 2006 282 I.J. Jureta, S. Faulkner, and P.-Y. Schobbens Although a large body of work deals with quality assurance in a processoriented manner, a non-negligible part of it relies on the usual Softgoal concept for the representation and reasoning about quality-related requirements. In doing so, procedural aspects of methods for dealing with quality during requirements engineering (RE) activities have been considerably developed, while conceptual foundations have not evolved in a notable manner. In particular, a more extensive view on the conceptualization and formalisms for representing and using quality requirements while taking into account their multi-facetted nature has not been proposed yet. We need to deal with requirements that are not only implicit, but also subjective, context-specific, imprecise, and ordered by preference. The work presented in this paper is a step towards a more profound understanding of requirements that are expressed usually in requirements goal diagrams (such as, e.g., i* [32]) as instances of the Softgoal concept. Overall, instances of the original Softgoal concept are seen as frequently containing information that is, not only subjective and context-specific (as assumed in the original definition), but also imprecise and involving preferences of the stakeholder who suggested the requirements modeled as the given softgoal. It is therefore suggested that the Softgoal is a multi-facetted concept that requires specialized techniques for dealing with its additional facets. This paper thus proves useful both in terms of advancing the understanding of a key concept in the RE modeling field, and in arguing that additional considerations need be taken into account when a RE method or framework that employs the Softgoal concept is being constructed and applied. Finally, the reader will undoubtedly notice that the discussion below is independent of a particular RE framework, which supports our arguments regarding the applicability of this discussion to many (at least goal-oriented) RE methods. The paper is organized as follows. Part of the literature on the treatment of quality requirements, applicable to the discussion in this paper is first overviewed. The bulk of the paper, which discusses and revisits the original Softgoal conceptualization is then presented. A set of general guidelines on the characteristics of RE methods aiming to employ the suggested conceptualization are presented. Finally, conclusions are summarized and directions for future work are identified.