What is a CDM?
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When designing a new database, you usually start at the "conceptual" level without having to worry about the details of the physical implementation.
A Conceptual Data Model (CDM) represents the logical structure of your database, independent of the database management system being used.
A CDM can contain data objects not (yet) available in the physical database, but does include all data objects needed to store all data with regard to the requirements of your database project.
With a CDM you can:
•create a graphical representation of data objects and their relationships, also called an Entity-Relationship Diagram (ERD)
•validate your model design before creating a physical database
•generate a physical diagram to any of the supported database systems
Note that "relationships" in a CDM are different from "foreign key constraints" in a PDM (or database) when it comes to their representation. A many-to-many relationship, for example, is a relationship between two entities with no intermediate entity, while in a PDM, such a construct will consist of 3 tables.
Next: Objects in a CDM.