Entity-Relationship Model

An entity–relationship model (ER model) is a high level model that is used to help design databases. This model is based on the notion of real world entities and the relationships existing between them.

  • Entities are real-world objects about which we collect data
  • Attributes describe the entities
  • Relationships are associations among entities
  • Entity set – set of entities of the same type
  • Relationship set – set of relationships of same type
 Consequently, the ER model becomes an abstract data model that defines a data or information structure that can be implemented in a database, typically a relational database.

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Limitations

  • ER model assume that information content can readily be represented in a relational database. This is not always feasible, say for unstructured and semi-structured data.
  • For many systems, possible changes to information important and require explicit specification.
  • The ER model was found unsuitable for multidimensional databases (used in OLAP applications).