![]() Such a model is the physical data model, or PDM.ĬDM is a set of strictly defined model elements. In other words, it is to first abstract the objective objects in the real world into entities (Entity) and relations (Relationship), it does not depend on a specific computer system or a DBMS system, this model is what we call CDM Then the CDM is converted into a data model supported by a certain DBMS on the computer. Usually people first abstract the real world into a conceptual world, and then turn the conceptual world into a machine world. It models information from the user's point of view, and is mainly used for conceptual design of databases. It uses Entity-RelationShip (ER) ) Theory as the basis, and expanded this theory. The data model is also called information model. ![]() The data model should meet the requirements of three aspects:ġ) It can simulate the real world more realistically Ģ) It is easy to be understood by people.ģ) It is convenient for computer to realize theĬoncept. This article mainly introduces the basic concepts of the conceptual data model CDM in PowerDesigner.ĭata model is an abstraction of data characteristics in the real world.
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