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Guideline (Intermediate,Concept & Evaluation) Do not reuse Dependums in more than one Dependency Relation. Open Version
Discussion: Dependency Link should have only one link segment on both sides of the Dependum: one on the Depender side and the other one on the Dependee side. Figure 1 depicts a split scenario where the Dependency Link splits into two links from one Dependum to two Dependees. This illustration says that “Patient” depends on both the “Government” and “Other health service providers” to fulfill or satisfy the Goal of, “Health Service Be Provided”. This notation violates the conventional Dependency Link in i* because it makes it difficult for the modeler and analyst to assess and evaluate the satisfaction of the Dependum when it is linked to two different Dependees. Because of the autonomicity of the Actors (Dependees) in i*, every Actor is evaluated separately in terms of its (her or his) contribution to the fulfillment and satisfaction of the Dependum. If the intention of the modeler is AND, the model should have Task Decomposition inside the Depender. The Dependums for the two Dependees will most likely by different. Using the split and join scenarios, however, are acceptable for drat models. Figure 2 depicts a join scenario where two Dependency Links from two Dependers join on one link from one Dependum to one Dependee.
The illustration shows both Dependers, “Patient” and “Citizen”, depend on the Dependee, “Hospital” to satisfy the Softgoal, “Availability [Health Service]”. This non-conventional i* notation, which has been used in one of the Tropos Methodology examples, follows the same lines of reasoning for the split scenario. The degree of satisfaction and Softgoal fulfillment for each Depender might have a different view whether the contribution of the Dependee can really satisfy the Softgoal of both Dependers.
Figure 3 illustrates another ambiguous scenario where two Dependency Links join on and split from the same Dependum. The two Dependums, “Medicine” and “Medicine’s Details”, are two different things that should not be represented by the one Dependum, “Medicine”. Using the proper Dependency Links enhances the accuracy of the model during model analysis and evaluation.
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