TimedGRL: Specifying Goal Models Over Time

Goal-oriented analysis allows performing trade-off analysis among competing solutions to a problem by determining which proposed solution strikes a more appropriate balance of stakeholder objectives and desired qualities of a system. Standard language definitions of common goal-oriented languages such as i*, the Goal-oriented Requirement Language (GRL), the NFR Framework, and KAOS offer varying support for such analysis. In most cases, however, the analysis is essentially confined to one snapshot in time. While several goal models may be created that represent different stages of a system, the current language definitions do not allow these models to be connected and make it difficult to analyze them simultaneously. Furthermore, many model elements need to be repeated in the models of the various stages, causing problems when these models need to be evolved consistently. This paper introduces TimedGRL, an extension of the GRL standard, which enables the modeling and analysis of a comprehensive set of changes to a goal model over time. The goal model and the changes to the goal model are captured in one model, which eases system evolution. The metamodel for TimedGRL is presented and an analysis algorithm for TimedGRL models is defined. The usefulness of TimedGRL is illustrated with an example from the sustainability domain.