ER to Relational TranslationCOMSATS INSTITUTE OF INFORMATION TECHNOLOGY, VEHARI

ER Diagrams

Entity

Relationship

Attributes

Some other symbols for ER-Diagrams

Multivalued attributes

Some other symbols for ER-Diagrams

Some other symbols for ER-Diagrams

Weak entity:◦ An entity that depends on another entity

Key attribute:o A key attribute is the unique, distinguishing characteristic of the entity

Some other symbols for ER-Diagrams

Multivalued attribute:A multivalued attribute can have more than one value. For example, an employee entity can have multiple skill values.

Derived attribute:A derived attribute is based on another attribute. For example, an employee's monthly salary is based on the employee's annual salary.

Some other symbols for ER-Diagrams

Composite attribute:◦ An attribute that has its own attributes.

Relationships in ER-Diagrams There are three types of relationships:

1. Binary relationship

2. Recursive relationship

3. Ternary relationship

Binary relationships◦ Relationship between two entities◦ Cardinality

◦ It has further 3 types:1. One to one relationship2. One to many relationship3. Many to many relationship

Binary relationships 1- One to one relationship

This relationship seems rare in this world

Binary relationships One to many relationship:

It reflects business rule in which one entity is related to many number of other entity.

Binary relationships Many to many relationship:

Many entities have relationship to many other entities

Recursive relationship

When an entity has relationship with its own.

Ternary relationship Relationship pf degree three is called ternary relationship

Participation Constraints in ER-Diagrams

Total Participation: Each entity in the entity is involved in the relationship. Total participation is represented by double lines.

Partial participation: Not all entities are involved in the relation ship. Partial participation is represented by single line.