Specimen Paper Computing

Large computer systems are often used for helping to forecast the weather. Describe why such computers are particularly useful in this application.

[4]

high capacity data storage - huge amounts of data are collected and processed.
calculations can be performed extremely fast
data collection can be automated - data input from weather sensors
data can be compared with previously stored data to predict future weather patterns

2(a)

Your Name Held 120 Times
in Government Files

This headline in a newspaper is introducing an article on the large amount of data duplication in personal information held by official organisations.

(i) Explain how a database could help to solve the problem of data duplication.

[2]

Any item of data is only stored once
The data is accessed through a linking key field

(ii) Give two reasons why people might be unhappy with this solution and explain in each case how their concerns might be eased.

[4]

There may be concerns over privacy of data - adequate security measures would need to be in place to ensure access is only allowed to authorised people.
People may not want to receive 'junk mail' - the database must not be made available to firms likely to produce this.

(b)

Give an example of how a query language might be used in an application of this type, making it clear what the result of your query should be.

[2]

Example taken from driving licence data....

SELECT driver_number WHERE (Licence_expiry_date - current_date) < 30

This selects all drivers whose licences expires within 30 days.

(c)

Explain briefly why primary key fields are so important in a database.

[1]

Each record is uniquely identified by its primary key field.

The Rocksound organisation sells compact discs (CDs) to members of the public via its web site, which contains a number of web pages, including a home page. Outline how a new visitor to the Rocksound web site will be able to find their way around it.

[2]

The home page would be loaded first.
Each page would have hyperlinks to other pages.
Browsers allow users to go back to the previously visited page.

..any two valid points...but you must mention hyperlinks!

4(a)

Wide area networks using packet switching are often used to transmit computer data.
Explain the term packet switching and give an example of the sort of information that would be transmitted in a packet.

[3]

A packet is a number of bytes of data which are passed around a network. The packet would consist of the data being sent, as well as the destination address of the packet.

(b)

Explain why communications protocols are required.

[1]

There has to be a consistent set of rules which would allow computers to communicate with each other. A computer receiving data needs to know how to interpret it.

5(a)

Data is often stored in indexed sequential files. These can either be single-indexed or multi-level indexed and can use an overflow area.

Using a diagram in each case, explain in detail each of these terms in the above paragraph:

(i) indexed sequential file

[3]

Records are sorted in order of the key field
An index of keys and block addresses may be used to locate records

Eg If record with key 1016 is required...

High Keys	Block Address
1010	34192
1020	34193	--Record 1016 would be stored in this block
1030	34194
...	...

(ii) multi-level index

[3]

the first index returns a secondary index...
..and this may occur several times before the block address is found.

Eg If Record 1016 is required...

High Keys	Index
1000	20
2000	21	Record 1016 is now looked for in index 21...
3000	22
...	...

Index 21 will give the block address...

Index 21 High Keys	Block Address
1010	34192
1020	34193	Record 1016 would be stored in this block...
1030	34194
...	...

(iii) Explain in detail the term overflow area in the above paragraph.

[2]

An area of storage separate from the main area...
...used to store records if the required block is full.

(b)

In other applications, data is held in random access files. Explain the term random access file, giving an example of an application which would need to use a random access file. Describe how records are located in a random access file.

[4]

A random access file allows direct access to a record without having to access other records first.
Example : An information retrieval system for travel agent.
A hashing algorithm is performed on the key field ...
... which results in the storage address of the record.

(c)

Explain the use of data encryption for the storage and transmission of data.

[2]

Data is coded to make it meaningless..
..and can only be decoded by an authorised person.

(d)

Explain when and why a transaction log is used.

[2]

A file of all the changes made .... used when a file is updated
in case of file corruption...the file can be re-created using a backup and the transaction log.

(e)

Outline the need for recovery procedures in a computer system.

[2]

If a computer system fails...
... it will be necessary to be able to re-create data files so that no data is lost.

6(i)

Explain the terms multiprogramming and time-slice.

[2]

More than one program is stored in memory and each is processed in turn.
A time-slice is a small amount of processing time allocated to a stored program.

(ii)

Describe how multiprogramming is achieved.

[2]

The operating system assigns priorities to loaded jobs
... and processes each job in turn until completed

(iii)

Describe the role of interrupts in a multiprogramming systems.

[2]

An interrupt is a signal from a device which needs attention. When a signal is received a 'flag' is set.
The operating system checks the flag regularly for an interrupt. If one has occurred it pauses what is being processed, services the interrupt and then returns to carry on.

(iv)

Describe the role of a scheduler within a multiprogramming operating system.

[2]

The scheduler decides the order in which jobs are processed...
...by assigning priorities to jobs

Each student at Cader Idris College is allocated to (exactly) one personal tutor, who is a lecturer in the College. Each of the lecturers uses a staff room, which he or she may share with one or more other lecturers. Most staff rooms have a telephone extension, though no staff room has more than one.

The table below shows part of the data held for a few of the students and their personal tutors. This data is held in a database.

Student Number	Student Name	Tutor Number	Tutor Name	Tutor Room	Tutor Telephone
6137	Morton, Lynne	407	Harris, Dave	215	492
6153	Khan, Imran	410	Adams, Jessica	214	495
6189	Evans, Elwyn	407	Harris, Dave	215	492
6192	Ho, Carol	408	Jones, Christine	220
6207	Vernon, Wayne	407	Harris, Dave	215	492
6208	Dodd, Debbie	414	Buckley, Ruth	215	492
6226	Evans, Elwyn	414	Buckley, Ruth	215	492
6228	Alton, Chris	407	Harris, Dave	215	492
6231	Mir, Razwana	425	Beaumont, Jim	214	495
.....	............	.....	..............	....	....

(i)

(I) State four other fields which it would be useful to store about each student.

[2]

home address
date of birth
parental contact number
medical problems

..make sure the fields are to do with the student...

(II) State four other fields which it would be useful to store about each lecturer.

[2]

qualifications
home address
date of joining the college
subject taught

(ii)

All the students are able to access some of the above data via the College network. Describe two restrictions that will be needed. Why is a database system particularly well suited to aiding security?

[3]

students should have read-only access to data and should not be allowed to make changes.
personal data about the tutors should not be accessed.

(iii)

(I) Explain the term third normal form.

[2]

data items in each table are dependent on the key only.
data items are dependent on the whole key

(II) Restructure this data into third normal form.

[6]

STUDENT (Student Number, Student Name, Tutor Number)

TUTOR (Tutor Number, Tutor Name, Room Number)

ROOM (Room Number, Room Telephone)

In the following question, additional credit will be gained if your answer demonstrates skill in written communication.

A robotic vehicle is to be launched from earth and sent to the moon to undertake exploration, including the analysis of minerals found on the moon's surface.

Describe how such a vehicle would be able to provide useful data for scientists on earth and describe its benefits and drawbacks compared with sending human astronauts to the moon.

[10]

The robotic vehicle would have a number of sensors fitted which could take readings of temperature, pressure, air content, etc. It would also have a digital camera fitted which could take images of the moon. There may also be the means of collecting rock samples and performing simple tests on these. All these readings would be transmitted back to earth for analysis by scientists.

There would be no danger to human life using this method as robots can operate in extremes of temperature and do not need air to breathe. There is no need for a return to earth and this would make the mission cheaper. There may be a problem if there is a breakdown in the robot as it may be impossible to fix it. A robot may also lack the reasoning power to react to a crisis for which it had not been programmed.