Automated synthesis and debugging of declarative models in alloy
In theory, formal specifications offer numerous benefits in developing more reliable software. In practice however, the use of specifications is rather limited, and practitioners often consider them more trouble than they are worth. Indeed, manually writing detailed specifications using notations that have unfamiliar syntax and semantics can be a daunting task -- even for experienced programmers. We introduce a new automated approach for synthesis of desired specifications and debugging of faulty specifications using given examples that capture the essence of desired properties and serve as test cases. Our focus is specifications written in the declarative language Alloy -- a first-order logic based on relations with transitive closure, and its SAT-based analysis engine. Our key insight is that a test-driven foundation enables modern approaches to synthesis and debugging of imperative code to serve as a basis for developing novel analogous techniques for declarative specifications. For synthesis, we build on equivalence in relational algebra and introduce techniques for generating candidate Alloy expressions. We also introduce a technique to complete a partial Alloy model with holes using constraint solving. For locating faults in buggy specifications, we build on mutation-based fault localization and introduce techniques for locating likely faulty nodes in the abstract syntax tree of the faulty specification. Moreover, we integrate our expression generation and fault localization techniques to introduce a technique for automated specification repair. We experimentally evaluate our techniques using several Alloy models as subjects, including those with real faults. The results show that our techniques are effective at synthesis and debugging of the subjects. We believe our techniques provide an important step towards increasing the role of formal specifications in developing more reliable software and realizing their promise.