What is Entity Relationship Model in DBMS?

  • In Data Modeling, an entity-relationship model (ERM) is a representation of structured data; entity-relationship modeling is the process of generating these models.
  • The end-product of the modeling process is an entity-relationship diagram (ERD), a type of conceptual data model or semantic data model.
  • The first stage of information system design uses these models to describe information needs or the type of information that is to be stored in a database during the requirements analysis.
  • The Data Modeling Technique can be used to describe any ontology (i.e. an overview and classifications of used terms and their relationships) for a certain universe of discourse (i.e. area of interest).

  • Entity & Entity sets
  • An Entity is an object that exists and is distinguishable from other objects. For instance, John Harris with S.I.N. 890-12-3456 is an entity, as he can be uniquely identified as one particular person in the universe.
  • An entity may be concrete (a person or a book, for example) or abstract (like a holiday or a concept).
  • An entity set is a set of entities of the same type (e.g., all persons having an account at a bank).
  • Entity sets need not be disjoint. For example, the entity set employee (all employees of a bank) and the entity set customer (all customers of the bank) may have members in common.

  • Relationship sets
  • Entity-relationship diagrams don't show single entities or single instances of relations.
  • Rather, they show entity sets and relationship sets.
  • Example: a particular song is an entity. The collection of all songs in a database is an entity set. The eaten relationship between a child and her lunch is a single relationship. The set of all such child-lunch relationships in a database is a relationship set.

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