Advantages and Disadvantages of ER Model Before discussing advantages and disadvantages of er model, let us give a brief introduction about what is ER model. In ER Model, objects of similar structures are collected into an entity set. The relationships between an entity sets is represented by a named E-R relationship, which may be (one-to-one,…

Generalization Specialization and Aggregation in DBMS Generalization Specialization and Aggregation in DBMS are abstraction mechanisms used to model information. The abstraction is the mechanism used to hide the superfluous details of a set of objects. For example, vehicle is a abstraction, that includes the types car, jeep and bus. So, the two abstraction mechanisms used to…

Supertype and Subtype with Example In the previous post (entity and its types) we define the concept of super and sub types. Let us thoroughly understand this concept. Let us assume an entity named EMPLOYEE. The entity employee has some attributes-empID, Name, Birth Date, Age etc. But sometimes we will have special employees that have some…

Identifying and Non Identifying Relationships – Relationships among the entities may be classified as being either Identifying Relationships Non Identifying Relationships Identifying Relationships – Definition 1 : In the previous post (Entity and its Types)  we define about weak entity types. These are the entities, which does not have a key attribute. So, To identify…

Types of Relationships in ER Diagram Different types of relationships in er diagram are – 1) Relationships based on degree, 2) Recursive Relationship. Let us discuss these one by one. Relationship and Relationship Set :   Relationships connect the entities and represent meaningful dependencies between them.It represents an association among several entities. Relationships sets is a…

Composite Entity Example – Composite Entity- As earlier said in previous post (entity and its types), Composite Entities are the entities which exists as a relationship as well as an entity. Consider the three types of connectivity – one to one cardinality one to many cardinality many to many cardinality A many to many relationship…