Analysis and design tools : E-R analysis
E-R MODEL
E-R Model means entity relationship model represents conceptual way of data modeling.
For every business system conceptual modeling is the intermediate phase that leads
to physical data base design. First step of conceptual data modeling is semantic analysis
which focuses on entities and their relationships. Some important basic concepts for
drawing E-Diagrams are as follows.
1. Entity: - An entity is an object that has its own unique identity.
For example: Any car, book, person, dream.[Important: Entity can be concrete or
abstract.]
2. Attribute: - An attribute is an aspect, characteristic or quality of either an entity or
relationship.
For example: color, size shape of a car can be the attributes.
3. Relationship: - A relationship is a meaningful association, linkage or connection
between entities.
4. Entity set: - Entity set is a set of entities of same kind.
For example: Accounts holder of same bank can form an entity set.
5. Relationship set:- A relationship set is collection of relations of same type.
Symbols of E-R diagram :
Technically if a relationship set contains a primary key it is called a strong entity set
otherwise it is called weak entity set. An entity may appear in I. One- one relationship II. One – many relationship III. Many –many relationship (m-n) 1] One- one relationship: (1:1) For a given occurrence of an entity there is exactly one
occurrence of another entity. For example: - Any one employee of an organization is identified by identity card.
2] One - many relationships: (1: M) For a given (value) occurrence of any entity there
can be more than one (value) occurrences of another entity.For example: A branch of bank has much number of customers. So it is 1-m relationship.
3] Many to many relationship: (m:n) There can be multiple occurrences of both the
entities that are being related For example: Subjects opted by students for a particular course.
example : 1. Production tracking is important in many manufacturing environments (e.g., the pharmaceuticals
industry, children’s toys, etc.). The following ER diagram captures important information in the
tracking of production. Specifically, the ER diagram captures relationships between production
lots (or batches), individual production units, and raw materials. 
