iStar is a goal-based requirements modelling language, being used in both industrial and academic projects of different domains. Often the language is extended to incorporate new constructs related to a particular application domain or to adjust it to practical situations during requirements modelling. Currently, the language is undergoing standardisation, and several studies have focused on the analysis of iStar variations to identify similarities and to define a core. This does not imply or constrain the need for iStar to continue to be extended. This paper contributes to the understanding of how iStar is extended by analysing how iStar researchers perform iStar extensions. To address this question, we followed a qualitative approach based on interviews involving 20 researchers from different research groups that proposed iStar extensions. The analysis revealed a good understanding about what extending a modelling language means and pointed out differences about how extensions are proposed. We discovered categories that impact positively on iStar extensions (such as reusing existing extensions, proposing extensions in abstract and concrete syntaxes, and creating new modelling tools), and other categories that impact negatively (such as modifying representations of the original constructs, proposing extensions in an ad hoc fashion and not carefully choosing graphical representations). We also evaluated the findings of interviews through an online survey answered by 30 iStar researchers. Finally, we proposed a set of guidelines to support the proposal for better future iStar extensions.
- Goal-based modelling
- Qualitative study