Program Synthesis from Formal Requirements Specifications Using APTS

Formal specifications of software systems are extremely useful because they can be rigorously analyzed, verified, and validated, giving high confidence that the specification captures the desired behavior. To transfer this confidence to the actual source code implementation, a formal link is needed between the specification and the implementation. Generating the implementation directly from the specification provides one such link. A program transformation system such as Paige’s APTS can be useful in developing a source code generator. This paper describes a case study in which APTS was used to produce code generators that construct C source code from a requirements specification in the SCR (Software Cost Reduction) tabular notation. In the study, two different code generation strategies were explored. The first strategy uses rewrite rules to transform the parse tree of an SCR specification into a parse tree for the corresponding C code. The second strategy associates a relation with each node of the specification parse tree. Each member of this relation acts as an attribute, holding the C code corresponding to the tree at the associated node; the root of the tree has the entire C program as its member of the relation. This paper describes the two code generators supported by APTS, how each was used to synthesize code for two example SCR requirements specifications, and what was learned about APTS from these implementations.