E-R model and Relational model are two types of data models present in DBMS. Let’s have a brief look of them:
1. E-R Model :
E-R model stands for Entity Relationship model. ER Model is used to model the logical view of the system from data perspective which consists of these components: Entity, Entity Type, Entity Set.
An Entity may be an object with a physical existence – a particular person, car, house, or employee – or it may be an object with a conceptual existence – a company, a job, or a university course. An Entity is an object of Entity Type and set of all entities is called as entity set. e.g.; E1 is an entity having Entity Type Student and set of all students is called Entity Set.
An Entity Type defines a collection of similar entities and set of all entities is called as entity set.
2. Relational model :
Relational Model was proposed by E.F. Codd to model data in the form of relations or tables. After designing the conceptual model of Database using ER diagram, we need to convert the conceptual model in the relational model which can be implemented using any RDMBS languages like Oracle SQL, MySQL etc.
Consider a relation STUDENT with attributes ROLL_NO, NAME, ADDRESS, PHONE and AGE shown in Table 1.
Let’s see the difference between ER model and relational model:
|S.No.||ER model||Relational model|
|1.||ER model is the high level or conceptual model.||It is the representational or implementation model.|
|2.||It is used by people who don’t know how database is implemented.||It is used by programmers.|
|3.||It represents collection of entities and describes relationship between them.||It represent data in the form of tables and describes relationship between them.||4.||It consists of components like Entity, Entity Type, Entity Set.||It consists of components like domain, attributes, tuples.||5.||It is easy to understand the relationship between entities.||It is less easy to derive the relationship between different tables.||6.||It describes cardinality.||It does not describes cardinality.|
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