iStar is a general-purpose goal-based modelling language used to model requirements at early and late phases of software development. It has been used in industrial and academic projects. Often the language is extended to incorporate new constructs related to an application area. The language is currently undergoing standardisation, so several studies have focused on the analysis of iStar variations to identify the similarities and defining a core iStar. However, we believe it will continue to be extended and it is important to understand how iStar is extended. This paper contributes to this purpose through the identification and analysis of the existing extensions and its constructs. A Systematic Literature Review was conducted to guide identification and analysis. The results point to 96 papers and 307 constructs proposed. The extensions and constructs were analysed according to well-defined questions in three dimensions: a general analysis; model-based analysis (to characterise the extensions from semantic and syntactic definitions); and a third dimension related to semiotic clarity. The application area targeted by the iStar extensions and their evolutions are presented as results of our analysis. The results point to the need for more complete, consistent and careful development of iStar extensions. The paper concludes with some discussions and future directions for this research field.
- Goal modelling
- Modelling language extensions
- Systematic Literature Review