Extending Alloy with Partial Instances

Kodkod, the backend of Alloy4, incorporates new features for solving models where part of the solution, that is, a partial instance, is already known. Although Kodkod has had this functionality for some time, it is not explicitly available to the modeller through the Alloy language syntax. We propose an extension to the Alloy language to make partial instances explicitly available to the Alloy user. Explicit partial instances are helpful for the Alloy user in a number of capacities, including test-driven development, regression testing, modelling by example, and combined modelling and meta-modelling. The proposed syntax also gives the modeller explicit access to the performance benefits of Kodkod’s partial instance features.