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In this paper we present some key concepts concerning the Properties Specification Language (PSL)

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In this paper the design criteria and the overall organization of MORIS, a new general purpose data management system, are illustrated.The system is based on a relational model of data, in which the data base is view ed as a collection of time varying relations of assorted degrees. The capabilities offer ed by this model are discussed. The archi--tecture of the system is illustrated,which is designed to provide independence of application programs from growths in data types and changes in data representation, con vertibility of data among different storage structures, and ability to provide solu tions to a wide variety of unanticipated user's problems in fast and uniform retrie val times.The relational mode] allows the formal definition of an user oriented language, based on applied predicate calculus. The capabilities of this language for retrieving any information which is, implicitly or explicitly, represented in the data base, are discussed.KEY WORDS AND PHRASES: data base management, data structures, storage structures, infor mation retrieval, transaction processing, relational model, data independence, security, predicate calculus.