Istituto di Scienza e Tecnologie dell'Informazione     
Degano P., Lomanto A., Sirovich F. On finding the optimal access path to resolve a relational data base query. Berlino: Springer, 1980.
The paper presents a formal model to specify a data base, a query and the access which must be followed to obtain the answer. The model is based on the problem reduction hypergraph, for which an admissible and optimal search algorithm is known. An effective method is given to map the data base and the query into a problem reduction hypergraph, which the known search algorithm can be applied to. The optimal solution to the problem reduction hypergraph provides an optimal (and possibly parallel) program to obtain the answer to the given query. Since the model allows to determine the correct answer, if any, without modification of the data base nor requiring further information, it is an improvement over the models presented in the literature.

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