Kodkod for Alloy Users

The generality of Alloy’s relational logic and the full automation of its analysis have prompted several attempts to use Alloy as a backend engine for other tools. However, these efforts have been hampered by the Alloy Analyzer’s lack of 1) a clean API, 2) support for partial instances, and 3) a mechanism for sharing subformulas and subexpressions. Designed expressly as a plugin component, the Kodkod relational engine overcomes these limitations. Unlike the Analyzer, Kodkod provides a simple interface for constructing and analyzing Alloy formulas; it accepts user-provided partial instances of these formulas; and it employs a robust scheme for exploiting shared formulas and expressions. This paper is an introduction to Kodkod for current Alloy practitioners. It describes the key differences between Kodkod and the Alloy Analyzer, including the meaning and utility of partial instances. A complete example that programmatically builds and analyzes an Alloy formula with Kodkod is presented, and results that compare Kodkod to the Alloy Analyzer on a series of benchmarks are discussed.