An entity–relationship model (or ER model ) describes interrelated
things of interest in a specific domain of knowledge. A basic ER model is
composed of entity types (which classify the things of interest) and specifies
relationships that can exist between entities (instances of those entity
types).
In software engineering, an ER model is commonly formed to represent things a
business needs to remember in order to perform business processes.
Consequently, the ER model becomes an abstract data model, that defines a data
or information structure which can be implemented in a database, typically a
relational database.