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
- 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).