Saturday, 27 July 2019

The Basic Building Blocks of ER Model

The proper and correct design of database is more important. The ER Modeling provides best way to develop database. ER modeling is a graphical representation tool and was developed to facilitates an easy implementation of business needs. So, so many companies today uses ER model to design their databases. Here you can learn what are basic thing used to draw ER model.

There are three basic building blocks of ER modeling: Entities, attributes, and relationships.

An Example of ER Model

1. Entity 

An entity is a “thing” or “object” in the real world that is distinguishable from all other objects. For example, The "employee" in a company is an entity, The students in a class is an entity. In ER modeling entities are represented using rectangle symbols.

In above example, The two entities students and class are shown in rectangle symbols.

2. Attributes

      These are the properties of an entity. For example, A students had his / here roll number and name. These two properties tells what he / here studying, that means they indicate what student. Such type of properties are called entities and they are represented using ellipse symbol.

In the above example, the attributes of student entity ( roll number and name) and class entity (subject name and hall ticket number) are represented using ellipse symbol.

An entity type or entity set is a collection of similar entities. Some examples of entity types are:
  1. All students in College, say STUDENT.
  2. All courses in College, say B.Sc.
  3. All departments in College, say Science. 
That means, all entities in a entity set have similar type of attributes or properties.

3. Relationship

It indicates how one entity related to another entity. It is an association between entities. For example, The student entity relates to class entity like this: The student attends classes to learn their course. That is here attends is a relationship between class and students, and it is represented by diamond symbol. Here is an example called works_In Relationship

  • Database Management System by Korth
  • Database Management System by Raghu Ramakrishna
  • Fundamentals of Relations Database system by Sumathi


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