L1 Introduction

Question 1

What are the three layers of abstraction in DBMS?

Answer 1

• physical: how data is stored.
• logical: based on a data model.
• view: what programs or user see.

Question 2

What are advantages of DBMS?

Answer 2

1. It saves programmer time by providing a declarativequery language, e.g. SQL.
2. It saves programmer time by automatically checking constraints.
3. It saves maintenance time by ensuring data independence.
4. It provides concurrent access to the database for multiple, simultaneous users.
5. It provides automatic recovery from failure.
6. It provides security to ensure appropriate access to data.

Question 3

What is a DBMS?

Answer 3

A DBMS is specialised software which is responsible for
efficient storage and retrieval of large amounts of data in
a database, allowing it to persist over long periods of time.

Question 4

What is physical data independence?

Answer 4

• Changes at one level of abstraction should not require changes at higher levels.
• Consists of two parts:
  
  1. physical data independence - the physical level may be changed without affecting the logical level.
  • growth independence - the independence of the view level from the addition of new structures to the database.
    * Deletions of structures at the logical level disrupt views that reference them.

Question 5

What is a data model?

Answer 5

A data model is a set of tables, linked by relationships and is an abstract model that organizes elements of data and standardizes how they relate to one another and to properties of the real world entities.