WOL: a language for database transformations and constraints

The need to transform data between heterogeneous databases arises from a number of critical tasks in data management. These tasks are complicated by schema evolution in the underlying databases and by the presence of non-standard database constraints. We describe a declarative language called WOL (Well-founded Object Logic) for specifying such transformations, and its implementation in a system called Morphase (an "enzyme" for morphing data). WOL is designed to allow transformations between the complex data structures which arise in object-oriented databases as well as in complex relational databases, and to allow for reasoning about the interactions between database transformations and constraints.