Question

1-Draw The ER diagram on the problem of your choice, depicting the 1:1 , 1:M and M:M relationship.

2-Explain with the pictorial representation the three schema architecture of DBMS.

Answer 1

• One to one relationship (1:1)

A single entity instance in one entity class is related to a single entity instance in another entity class.

eg: Each student in an examination hall fills one seat and one seat is assigned to only one student.

• One to many relationship (1:M)

A single entity instance in one emtity class is related to multiple entity instance in another entity class.

eg: A child can only have one father biologically but a father can have multiple child.

• Many to many relationship (M:M)/(M:N)

   Each entity instance in one entity class is related to multiple entity instance in another entity class and vice versa.

eg: A customer can take many item on rent. An item can be rented by many customers.

2.

Three schema architecture is used to describe the structure of a specific database system. It contains three level namely physical level, logical level, view level.

• Internal/physical level- Physical storage structure of database is described in this level, here the complex low level data structures are described.This level has the lowest level of abstraction.

• Conceptual level - Describes the structure of the database as whole. It describes what data are to be stored in database and also describes the relationship among these datas.
• External/view level - Describes the db from the users view. This level has the most abstraction ie, the internal and conceptual scheme is hidden from the users view.