4.3.2 Softgoal Dependency

In a softgoal dependency, a depender depends on the dependee to perform some task that meets a softgoal. A softgoal is similar to a goal except that the criteria of success are not sharply defined a priori. The meaning of the softgoal is elaborated in terms of the methods that are chosen in the course of pursuing the goal. The depender decides what constitutes satisfactory attainment of the goal, but does so with the benefit of the dependee’s know how.
Based on all the concepts presented in Section 4.3 “Strategic Dependencies”, the modeler has the choice of using a Task, Resource, Goal, or Softgoal Dependency Link between actors in a model depending on the context of the design. Each case has different purpose and interpretation. For example, using a Task Dependency Link between two actors means that one of these actors actually depends on the other actor to satisfy and perform the task in a particular way or with some freedom given a set of constraints. Therefore, the task is delegated to another actor with minimum or no freedom of choice. On the other hand, using a Goal or Softgoal Dependency Link means that the Depender actually gives more freedom in choosing which methods to employ to satisfy the dependency or accomplish the Goal or Softgoal.

Additionally, some literature refers to Softgoals as Non-Functional Requirements (NFRs). There are examples, however, of non-functional requirements that are not softgoals. Anything that is quantified is not a softgoal, but can be an NFR. For example, the system must process an order within 2 seconds, an NFR, but not a softgoal. Despite this debate whether Softgoals and NFRs are the same thing, it is still acceptable for beginner users of i* Guide to assume that the term NFR constitutes the same concepts discussed above in regards to Softgoals.





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Variation: Contribution Polarity on Softgoal Dependencies

In the version of i* used in the reference listed below, softgoal dependencies are assigned a polarity to indicate whether they positively or negatively contribute to the recipient softgoal. These contributions are described using + and -. See an example in Figure 1.


Figure 1: An example of Contribution Polarities on Softgoal Dependencies (Figure from Reference)

Reference: X. Franch, “On the Quantitative Analysis of Agent-Oriented Models”, 18th International Conference on Advanced Information Systems Engineering (CAiSE’06), pp. 495-509. LNCS, vol. 4001. 2006.

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