Databases

Question 1

Explain the properties of Serial Files:

How data is stored, the order of data and usage

Answer 1

• Data stored in the order it is entered.
• No order for the data is maintained.
• Used for transaction files.

All data stored on one file.

Question 2

Explain the properties of Sequential Files:

How data is stored, the order of data and usage

Answer 2

-Data is stored in order of a key field.
-Order maintained as new records are added.
- Useful for master files.
(Was kept on magnetic tapes).

All data stored on one file.

Question 3

What is an Indexed Sequential File?

Answer 3

An index is maintained to allow groups of records to be quickly accessed.

Question 4

Define a Database:

Answer 4

A database is a structured, persistent collection of data..

Question 5

What does persistent mean?

Answer 5

The data is retained after the software has finished processing it.

Question 6

What are the advantages of databases over files?

Answer 6

• More efficient for processing.
• Reduce storage requirements.
• Avoid redundancy (duplicate data).
• Allow different users to only see relevant data.

Question 7

How are databases managed?

Answer 7

They are managed by a DBMS (Database management system).

Question 8

What does a DBMS do?

Answer 8

• Provides a manipulation language to access/change data.
• Provide additional security.
• Provide an interface for other programs to access data.

Question 9

Give an example of a DBMS

Answer 9

Microsoft Access.

Question 10

What do databases consist of?

Answer 10

Tables (entities or files) that store data in rows (records/tuples) and columns (fields/attributes).

Question 11

What is an entity?

Answer 11

A ‘thing’ in which data is recorded for. It is the actual table in a database.

Question 12

What is a record?

Answer 12

A record/tuple is the row in a database.

Question 13

What is a field?

Answer 13

The column in a database.

Question 14

What do queries do?

Answer 14

Allow the modification of data.

Question 15

Give some examples of a query:

Answer 15

Search, add, delete and sort.

Question 16

What is a Flat File database?

Answer 16

-A single table (all data stored in one table)

Question 17

What are the disadvantages of a Flat File database?

Answer 17

• They are harder to query.

- Data may be duplicated (inefficient use of memory).

Question 18

What is a relational database?

Answer 18

• A database consisting of multiple related tables

eg students, subjects studied and tutor groups.

Question 19

What is the advantage of a relational database?

Answer 19

They are easier to query.

Question 20

Explain a one to one relationship:

Answer 20

One record in one table is related to one record in a different table.
eg Country and Prime Minister.

Question 21

Explain a one to many relationship:

Answer 21

One record in one table is related to many records in another table.
eg Tutor group (one record) and Students (many records).

Question 22

Explain a many to many relationship:

Answer 22

Broken down into two one to many relationships with an extra table used between them.
eg Cars and Parts becomes Cars —-= Car Parts=—- and Part

Question 23

What is used to denote a ‘many’ side of a relationship?

Answer 23

Three lines spreading out from a single line.

Question 24

What is a primary key?

Answer 24

A unique identifier assigned to the field of each record in a table.

Question 25

What is a Secondary Key?

Answer 25

An alternative identifier that can be used in a search if the primary key is unknown or impractical to use.

Question 26

What is a primary key used for?

Answer 26

Used in the index to help quickly search the database.

Question 27

How are tables linked?

Answer 27

Through the use of a common attribute. This attribute is a primary key of one table and a foreign key of another.