Understanding Entity Relationship Diagramming
With the early stage business analysis complete, you're ready to move on to the actual modeling of the database. An entity relationship diagram (ERD) is a logical representation of your database that presents just such a model. An ERD is a logical model and may also be a physical model. A logical model is not system specific. Stated differently, the logical model is not unique to any specific database system, such as SQL Server or Oracle. The physical model specifies exactly how a logical model would be implemented within a specific system. You would need a different physical model for SQL Server than you would for Oracle.
You cannot store data in an ERD, nor can you retrieve data from an ERD. However, ...
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