The design of an organization's information system requires the development of numerous models: data, processing, usage, flow of information. Data models are necessarily undertaken before the creation of databases. Usually there are three levels of modelling. The Conceptual Data Model (CDM) focuses on large data structures and their relationships regardless of the technologies used in the computer system. It often results in the form of an Entity-Relationship Model. The Logical Data Model (LDM) prepares for the implementation of the data at the physical level as a relational database or, more rarely now, as simple files. The logical model in a relational database transforms the conceptual entities into attribute tables, determining the primary keys from the properties of the identifier. The observation of minimum and maximum cardinality of each association indicates whether a new key must be added to an existing table (cardinality [0, n]) or if the association requires the creation of a new table. The Physical Data Model (PDM) is the creation of tables in the DBMS, or files on the hard drive.
[French: Modèles de données]