Week 2

Question 1

What are the objectives/goals of three-level database architecture?

Answer 1

All users should be able to access the same data
DBA should be able to change the database storage structures without affecting users view
Internal structure of database should NOT be affected by changes to physical aspects of storage

Question 2

Name and explain the three levels of three-level architecture.

Answer 2

External level = Users view of the database. Describes the part of the database relevant to the user.
Conceptual level = Communities view of the database. Describes what data is stored in the database.
Internal level = Physical representation of the database.

Question 3

What is the meaning of logical data independence?

Answer 3

Refers to the immunity of the external schema to changes in the conceptual schema

Question 4

What is the meaning of physical data independence?

Answer 4

Refers to the immunity of the conceptual schema to changes in the internal schema

Question 5

What is conceptual modelling?

Answer 5

Is the process of developing a model of information that is independent of implementation details. Conceptual schema is the core of a system supporting all users.

Question 6

What is a system catalog? and why is it important?

Answer 6

A system catalog is a storage of information (metadata) describing the data in the database. It is important and it stores important items such as names, types and size of data items as well as the names of the authorized users.