Generating Queries from Complex Type Definitions

Many information systems are implemented as application programs connected to a database system. A characteristic problem of such systems is the famous impedance mismatch, i.e., the conceptual distance between the programming and the database languages. The traditional solution is to implement an interface that transforms one representation into the other. Commercial database systems ooer prepro-cessors that allow to embed the database language (e.g., SQL) into the programming language (e.g., C). Such an approach frees the application programmer from the task to specify details of the communication. However, the impedance mismatch is not solved but aggravated. The set-oriented database language is intermixed with the element-oriented programming language, a notorious cause for programming errors. Moreover, there is no support in mapping the restricted data representation of databases into the more complex type system of programming language. This paper proposes an intermediate language, the API modules, for specifying the relationship between the representations in the database and in the application program. The query for retrieving the information and the data types for storing it can be generated from the API module. The modules are simple enough to allow reasoning on queries generated from them.