Structured management of model base has placed demands on some kind of computer based frameworks with highly structured formalisms. This paper proposes a new framework, called the relational algebraic system entity structure (RASES), which is based on the system entity structure (SES) formalism and the relational algebra (RA) formalism. These formalisms provide a conceptual basis for the structured model base management. Within the framework, structural knowledge of a system is represented in a hierarchical structure and saved in a database. Furthermore, several operations can be formulated in terms of relational algebra which can be coded in a standard query language such as the SQL. The framework can be easily implemented on, and fully utilize the functionality of, relational database management system (RDBMS). With the help of the implemented framework, simulation models can be systematically synthesized from the models in the model base through the following processes. First, a family of hierarchical structures of a system is organized in the form of entity structure by the entity structuring process. Then, candidate models of the system which meet design objectives are synthesized from the entity structure through the pruning process. Finally, designers can conduct appropriate experiment with the models for design verification and performance measure. ？ 1997 Elsevier Science B.V.