December 1999
SW204 : SOFTWARE AND
FILE DESIGN

QUESTION 1 (Compulsory)

Total Marks: 30 Marks

• Question 2
• Question 3
• Question 4
• Question 5
• Cover Page

SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
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(i)What is another name for a short term scheduler ?[1 mark ]
CPU scheduler.

(ii)How does a short term scheduler work?[1 mark ]
It selects the process in the ready queue and allocates it CPU.

List two non preemptive scheduling algorithms.
One mark should be awarded for each algorithm named (up to a maximum of two marks).

•First Come First Served.

•Shortest Job First.

•Priority Scheduling.

Name the two ways of implementing fixed partitioning .
Separate input queues (1 mark)and single input queues (1 mark).

Under what circumstances is spooling useful?
When dedicated I/O devices are being used in a ultiuser environment. Other valid answers should also receive credit.

When can deadlock occur?
Deadlock occurs when several processes are interlocked,each one waiting for resources held by another waiting process. Other valid answers should also receive credit.

Describe two objectives of language translation.
One mark should be awarded for each valid point,and a further mark should be awarded for each satisfactory elaboration (up to a maximum of four marks).

•Instruction statement conversion (1 mark).High level language is converted into low level language (1 mark).

•Source code error detection (1 mark).Any source code errors are identified, and error messages are generated (1 mark).

•Object code optimization (1 mark).Object code which is compact and efficient is produced (1 mark).

(i)Describe two advantages of off-the-shelf packages.[4 marks ]
(i)One mark should be awarded for each valid point and a further mark should be awarded for each satisfactory elaboration (up to a maximum of four marks). Examples include the following:

•Implementation (1 mark).The implementation is cheaper and quicker (1 mark).
•Systems design,programming,and testing (1 mark).It is cost-effective, as there is reduced effort in terms of analysis,design,and programming (1 mark).
•EDP expertise (1 mark).Small organizations can make use of high quality software without having the relevant expertise in the company (1 mark).
•System documentation (1 mark).Off-the-shelf packages are usually well documented (1 mark).
•Portability (1 mark).Off-the-shelf packages are sometimes portable between different systems (1 mark).
Other valid answers should also receive credit.

(ii)Describe one disadvantage of off-the-shelf packages.[2marks ]
One mark should be awarded for each valid point and a further mark should be awarded for a satisfactory elaboration.Examples include the following:

•Suitability (1 mark).An off-the-shelf package is more likely to be suitable for general requirements,rather than specific requirements (1 mark).
•Ease of maintenance (1 mark).It may be very difficult (if not impossible)to modify or tailor an off-the-shelf package to meet specific needs (1 mark).
•Inefficiency (1 mark).An off-the-shelf package may be inefficient as it may include irrelevant functions (1 mark).
Other valid answers should also receive credit.

Name two techniques which may be used for reducing disk access.
Caching (1 mark)and reducing the amount of disk arm motion (1 mark).

(i)List two advantage associated with the use of sequential files.[2marks ]
One mark should be awarded for each valid advantage named (up to a maximum of two marks).Examples include the following:

•File design is simple.
•Efficient for high activity files.
•Effective use of low cost file media.
•Suitable for batch transactions.
Other valid answers should also receive credit.

(ii)List two advantages associated with the use of random files.[2marks ]
One mark should be awarded for each valid advantage named (up to a maximum of two marks).Examples include the following:

•Fast access for low hit-rate processing.
•Handles volatile files easily.
•Does not need room for indexes.
•Suitable for processing when transactions cannot be batched or sorted.
•May be created over a long period of time.
•Can generate a manageable address from an unmanageable key. Other valid answers should also receive credit.

Describe the three essential elements of an expert system .
One mark should be awarded for naming each component,and a further mark should be awarded for each satisfactory elaboration.

•The knowledge base (1 mark).The knowledge base is domain specific and contains unconditional factual statements derived from data stores (1 mark).
•The inference engine (1 mark).The inference engine is used to derive results or infer conclusions from the knowledge base (1 mark).
•The user interface (1 mark).The user interface obtains user requests, submits requests to the inference engine for processing,and interacts with users to define problem areas (1 mark).