CP5 Computing June 2004

1(a)

Giving an example, explain the term buffer when used in a computer system.

[2]

An area of memory which is used as a temporary storage area
Eg - when data is sent to a printer it is stored in a buffer first. When the buffer is full, the data is sent to the printer.

(b)

Explain double buffering and give an advantage over single buffering.

[2]

two buffer areas are used. While one buffer is being emptied the other is being filled.
this speeds up the process and is faster than using a single buffer.

2.(a)

Data can be transmitted on the Internet using packet switching.

(i)

Give two examples of the kind of information that would be contained in a packet.

[2]

the data being transmitted
the address of the destination of the data

(ii)

Explain in detail the term packet switching.

[2]

data to be transmitted is split up into a number of packets
...and each of these is transmitted possibly through different routes to its destination where the data is re-assembled.

(iii)

State one advantage of packet switching over circuit switching.

[1]

as the data can travel different routes it is not affected by a link which is not working.

(b)

What is meant by the term bridge in a computer network?

[1]

a bridge links two networks together to allow communication between them.

3. (a)

Operating systems rely on interrupts.

(i)

What is a computer interrupt?

[1]

a signal from a device to the processor

(ii)

Describe three conditions or events that could generate a computer interrupt.

[3]

a device failure
a device which needs attention - eg paper out in a printer
a run-time error eg division by zero

(iii)

What is meant by the term interrupt priority? Explain why some interrupts have a higher priority than others.

[2]

a priority is a value assigned to an interrupt which indicates its importance.
some interrupts (high priority) will need to be serviced before others (low priority).

(b)

The status of a process could be running, ready or blocked. Briefly explain the term ready.

[1]

no processing is occurring but it is waiting for eg some input

4. (a)

Data is often stored in indexed sequential files that make use of an overflow area.

(i)

Explain in detail how a record is added to an indexed sequential file.

[2]

the keyfield is looked up in the index to find the block where the record is to be stored
the record is inserted into the records in the block in sequential order

(ii)

What is an overflow area and why is an overflow area required?

[2]

an area of the file where records are stored. If a block is full a new record will need to be stored in an overflow area.

(iii)

Explain in detail how a record would be stored in an overflow area of an indexed sequential file.

[2]

the index indicates a block where a new record is to be stored.
If the block is full, then a pointer is left in the block to show the address of the overflow area where the record is stored.

(iv)

Access to records in the overflow area is slower than using the index directly. How could the file and index be re-organised to remove all records from the overflow area?

[2]

the file would need to be reorganised either with larger blocks
...or with smaller sections in the index. This would mean fewer records stored in each block.

(b)

File privacy is important in a computer system, explain why some users should not have access to all files. Apart from passwords, describe in detail one method of providing file privacy.

[3]

some files may contain personal information which may be embarrassing for the individual or may contain credit card or bank details which may be used by criminals.
when data is stored it may be encrypted using special coding techniques.
only authorised people would be able to decrypt the data stored.

5. (a)

Explain each of the terms simplex, half duplex and full duplex transmission.

[3]

simplex - data can only be transmitted in one direction
half-duplex - data can be transmitted in both directions but only one direction at a time
full-duplex - data can be transmitted in both directions at the same time

(b)

Data from several communication lines has to be transmitted along one communication line. What device would be required to perform this transmission?

[1]

a multiplexor

6. (i)

Using an example, explain the term distributed processing.

[2]

instead of having one large computer, distributed processing uses a number of different computers to perform a common task
example - an airline traffic control system may use a number of different computers around the country but all linked together to control the flight of planes

(ii)

Describe one advantage of using this type of processing.

[1]

there is no need for a large and expensive computer

The air conditioning and heating systems of a hotel are controlled by a computer. The control systems use feed-back to maintain the temperature in the hotel between 20^oC and 23^oC at all times.

(a) (i)

Explain what is meant by the term feed-back.

[2]

the output of the computer affects the sensor readings used as input

(ii)

Describe one benefit to the hotel guests and one benefit to the hotel owners of using a computer-controlled environment for the hotel.

[2]

a comfortable temperature is constantly maintained.
there is no need for human intervention, the system is automatic and constantly working.

(b)

The computer will require digital input. Explain the difference between digital and analogue signals. Describe where analogue to digital conversion will be required in the hotel's system.

[2]

digital data has distinct possible values; analogue data can be any numerical value within a given range.
computers process digital data, but temperature is an analogue quantity, so conversion of the data needs to take place.

An electrical goods retailer allows customers to make purchases using the Internet. When placing an order the customer has to access the stock database to determine whether the item they want to purchase is in stock.

The retailer has taken steps to ensure hackers cannot corrupt the database. Describe two problems that may accidentally arise due to customers having access to the stock database and explain how the retailer could attempt to solve these problems.

[4]

a customer may access the stock file and see that an item is there but in fact the last one has already been sold
a real-time system must be in place so the stock file is immediately updated when a sale takes place.
incorrect data may have accidentally been written onto the stock database
there should be data validation techniques operating

9. (a)

Explain the difference between a primary key and a foreign key in a relational database, and explain the function of a foreign key.

[3]

the primary key of a table uniquely identifies each record in it
a foreign key is a field in a table which is the primary key of a different table
the foreign key provides a link between the data in two different tables.

(b)

Using an example, explain what is meant by the term data redundancy in a database.

[2]

if the same data is stored in two different tables then this is data redundancy
Eg a pupil's name may appear in a class list as well as an exam results table

(c)

Using an example, explain what is meant by the term data inconsistency in a database.

[2]

if the same data is stored twice in different tables, it may not be exactly the same
a pupil's name 'John Smith' in the class list may be stored as 'John Smyth' in the exam results.

(d)

Patients in a large hospital have one doctor who is responsible for their welfare. Each patient is assigned to one ward.

The table below shows a sample of patients, their doctors and their wards.

Restructure the database shown below into third normal form using three tables. There is no need to copy the items of data.

Patient Code	Patient Name	Patient DOB	Ward Code	Ward Name	Number of Beds	Doctor Code	Doctor Name	Doctor Tel Number
P2356	John Jones	12/03/76	W34	Everest	24	D887	Dr Patel	656
P3426	Phillip Davies	04/06/81	W22	Snowdon	30	D769	Dr Smith	298
P1981	Gareth Evans	27/12/45	W08	Kilimanjaro	16	D887	Dr Patel	656
P1765	Jane McBride	23/10/65	W45	Ben Nevis	4	D157	Dr Lloyd	388
P0878	Suzan Iqbal	17/07/69	W34	Everest	24	D752	Dr Jones	411
P9872	Jane Howells	04/06/82	W34	Everest	24	D157	Dr Lloyd	388
P7658	Izmir Khan	27/12/71	W15	Blanc	9	D989	Dr Castillo	437
P2569	Juan Garcia	23/10/64	W08	Kilimanjaro	16	D887	Dr Patel	656

[8]

PATIENTS(PatientCode, PatientName, PatientDOB, WardCode, DoctorCode)
WARDS(WardCode, WardName, NumberOfBeds)
DOCTORS(DoctorCode, DoctorName, DoctorTelNumber)

10.

In the following question, additional credit (up to 3 marks) will be given if your answer demonstrates skill in written communication.

A private health company provides clients with access to a secure Internet site where they can:

use a diagnostic expert system
consult interactively with a doctor
access huge amounts of medical information

Briefly describe how a client could make use of the three facilities given above.

Describe any benefits for the clients or for the company that this Internet site may provide. Describe any drawbacks for the clients or for the company that using the Internet site may have.

[7+3]

The client may search the expert system for information about a particular medical condition and view recommended methods of treatment. They could also use the diagnostic part of the system by inputting the symptoms and asking the system to suggest various causes of the problem.

The interactive consultation would involve a conversation between the client and the computer in the form of questions and answers.

The benefit for the client is that this can be done in complete privacy from home without the need for making appointments to see a doctor. The company benefits by releasing their medical experts for things other than seeing clients, and can provide consultations to a larger number of clients in less time.

The human touch factor may be a drawback to the client. It may be easier to explain a problem to a human doctor than to a computer.

The company will need to employ computer experts to keep the site up-to-date with all the latest medical information.