In this paper we describe a method for encoding software models as Prolog programs, and how to use these programs to support incremental development. Requirements, alternative designs, and implementation patterns are encoded as predicates in the program, and define a search routine, the solutions of which are possible implementations of the requirements. Under default operation, this routine validates that a given parsed code is compatible with one of these solutions. Additionally, the same search routine can be executed by special interpreters that provide traceability and code generation as well. Code generation may be complete or partial, allowing the user to combine hand-written and generated code. By customizing the interpreter, the user can generate an outline of the design or a tasks list, instead of code. We demonstrate these techniques using Java and SQL, but our approach is applicable to other programming languages and paradigms as well.