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Alloy: Alloy Analyzer
built 615 days ago
Alloy is a structural modelling language based on first-order logic, for expressing complex structural constraints and behaviour. The Alloy Analyzer is a constraint solver that provides fully automatic simulation and checking. Alloy has been developed by the Software Design Group at MIT. The first Alloy prototype came out in 1997, and was a rather limited object modelling language. Later versions added quantifiers, higher arity relations, polymorphism, subtyping, and signatures (Alloy's structuring mechanism). The performance and scalability of the tool have gradually increased.
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Through version 3.0, the Alloy Analyzer incorporated an integral SAT-based model-finder based on an off-the-shelf SAT-solver. However, as of version 4.0 the Analyzer makes use of the Kodkod model-finder, for which the Analyzer acts as a front-end. Both model-finders essentially translate a model expressed in relational logic into a corresponding boolean logic formula, and then invoke an off-the-shelf SAT-solver on the boolean formula. In the event that the solver finds a solution, the result is translated back into a corresponding binding of constants to variables in the relational logic model.[2]
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The Alloy Analyzer is essentially a compiler. It translates the problem to be analyzed into a (usually huge) boolean formula. This formula is handed to a SAT solver, and the solution is translated back by the Alloy Analyzer into the language of the model. All problems are solved within a user-specified scope that bounds the size of the domains, and ... makes the problem finite (and reducable to a boolean formula).
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In order to keep the model-finding exercise tractable, the Alloy Analyzer performs model-finding over restricted scopes consisting of a user-defined finite number of objects. This has the effect of limiting the generality of the results produced by the Analyzer. However, the designers of the Alloy Analyzer justify the decision to work within limited scopes through an appeal to the small scope hypothesis[1]: that a high proportion of bugs can be found by testing a program for all test inputs within some small scope.[3]
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Alloy Analyzer