Revision

Question 1

Another method of input is forms dialogue. Outline what is meant by forms dialogue
and explain how this approach can provide input validation. [2]

Answer 1

The computer prompts for input into specific fields on a screen dialogue box.
Many inputs may be via combo boxes, radio buttons, etc, so only certain entries are allowed.

Question 2

Describe the difference between rounding and truncation. [2]

Answer 2

Rounding: number is approximated to nearest whole number/tenth/hundredth, etc
Truncating: number is approximated to whole number/tenth/hundredth, etc, nearer zero (accept
lower)

Question 3

State the main difference between a flat file system and a relational database. [1]

Answer 3

A flat file is database held as a table and stored in a single file, whereas a relational database
normally contains a number of linked tables.

Question 4

Explain the role of the DMBS in allowing authorised users to data [2]

Answer 4

Any two of:

The DBMS allows access via passwords.
The DBMS allows certain users access to certain records or fields only.
The DBMS may allow read and/or write access only.

Question 5

What is the purpose of Backus-Naur Form (BNF)? Explain why BNF is often used
in preference to a natural language such as English or Welsh. [2]

Answer 5

BNF is used to describe (unambiguously) the syntax / grammar / rules of a programming /
computer language.
Natural languages such as English or Welsh are normally ambiguous/imprecise.

Question 6

Explain why careful version control is necessary when developing computer
programs. [1]

Answer 6

Any 1 of:
 If programmer A modifies current version, and programmer B modifies an earlier version,
neither new version will contain both modifications
 Any amendments must be made to the most recent versions

Question 7

Explain the difference between a procedural and non-procedural programming
language. [2]

Answer 7

Procedural languages are concerned with: any one of:
 carrying out actions / calculations, etc
 obeying (ordered) set of instructions
Non-procedural languages are to do with facts / rules / making queries
Marking: Two of the above are needed for the mark

Question 8

Explain the role of a link loader and give an example of a linking error. [2]

Answer 8

A link loader is a software tool which combines already compiled modules/subprograms into
the executable program.
Example of error - any one of:
 link loader cannot find a compiled module/subprogram / it doesn’t exist
 the number or type of parameters provided is wrong

Question 9

Give a range of events where an interrupt would occur: [8]

Answer 9

Situations giving rise to interrupts: any two of (Must indicate S/W or H/W):
 May arise from a run time error (S/W)
 May arise from input/output request (S/W)
 May arise from a user request (S/W)
 May arise from a software fault (S/W)
 May arise from a peripheral e.g. keyboard key pressed (H/W)
 May arise from a peripheral e.g. printer run out of paper (H/W)
 May arise from e.g. a timer pulse (H/W)
 May arise from a hardware fault (H/W)
An example of an extended answer worth four