ON THE USE OF STATIC TYPING TO SUPPORT OPERATIONS ON FRAMEWORKS

Frameworks capture the commonalities in design and implementation betw een a family of related applications and are typically expressed in a general-purpose object-oriented language. Software engineers use frame works to reduce the cost of building complex applications. Although th e task of using a framework to build an application is error-prone, fe w techniques and tools exist to aid the engineer. This paper character izes the operations of instantiation, extension and refinement used to build applications from frameworks and explores how these operations are supported by one common language-level tool, namely the static typ ing policies (and associated tools) of common object-oriented language s. It was found that both conservative contravariant and covariant sta tic typing policies were effective in supporting the operations of fra mework instantiation and framework extension. However, both policies w ere ineffective at supporting the operation of framework refinement. A lthough it does not support the refinement operation itself, covarianc e is sufficiently expressive to support the instantiation of a properl y refined framework. This result provides a basis for defining and bui lding tools to support the effective use and evolution of frameworks i n software engineering environments.