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With current database technology treads, there is an increasing need to specify and handle complex schema changes. The existing support for schema evolution in current OODB systems is limited to a pre-defined taxonomy of schema evolution operations with fixed semantics. Given the variety of types, complexity, and semantics of transformations, it is sheer impossible to a-priori provide a complete set of all complex changes that are going to meet all user's needs. This paper is the first effort to successfully address this open problem by providing an extensible framework for schema transformations. Our proposed SERF framework succeeds in giving the user the flexibility to define the semantics of their choice, the extensibility of defining new complex transformations, and the power of re-using these transformations through the notion of templates. In this paper we now formally show how the templates guarantee the schema consistency under more complex transformations. To verify the feasibility of our SERF approach we have implemented one realiztion of our concepts in a working prototype system, called OQL-SERF, based on OQL, ODMG, MetaData and Java's binding of ODL. To validate the completeness of our approach, we have also conducted a case study demonstrating that our SERF approach can handle all the schema evolution operations we identified from the literature.