Contract-Oriented Specifications

In classes developed using design-by-contract, contracts contain assertions that formalise preconditions, postconditions and invariants. To be sure that contracts are complete, they can be derived from specifications. For classes in a data structures library, equational specifications are appropriate. However, a conventional equational specification cannot usually be mapped directly to contracts. Instead, a second, contract-oriented, equational specification can be devised, with two key properties: it can be proved that the contractoriented specification implies the original specification; and the contract-oriented specification can be mapped systematically to contracts. These two properties combine to increase confidence that the contracts capture the same abstraction as the equational specification.