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Computer Science by Ian Sinclair

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Computer Science
Suggestions for practical work
1 Use a hashing program to generate hash numbers from names and
numbers and check the effects of collisions.
2 Compare the search time needed by a hashing algorithm as com-
pared to a linear search, both working on the same long file of
names.
3 Use Prestel to find information such as times of flights to Paris, and
comment on the number of selection steps needed to retrieve the
information.
4 Use a commercial accounts package and list the data validation
methods that are used.
Multiple-choice test questions
1 The fastest method of retrieving a record from a random-access file is by
using:
(a) linear search
(b) hashing
(c) binary search
(d) Btree
2 A file of names is being sorted into alphabetical order, and is first
converted into uppercase. This is done because:
(a) only uppercase names can be sorted
(b) names never start with lowercase letters
(c) uppercase names are easier to sort
(d) it allows the use of ASCII codes for sorting order
3 The fastest types of sorting algorithm for large files depend on:
(a) inserting items into the correct position in a new file
(b) repeatedly going through the list interchanging items that are in the
wrong order
(c) dividing the list into sections and comparing items in two sections
(d) comparing the last item in the list with the first
4 A customer gives an address as 37 Fairway Ave. The computer can query
this if one of its files contains the entry:
(a) Fairway Ave < 31
(b) Fairway Ave > 31
(c) Fairway Ave
(d) 37
5 To ensure integrity of a file you should:
(a) make another copy on the same disk
(b) make another copy on tape
122
File processing and management
(c) keep two other copies on other media
(d) make a printout of the data
6 The greatest risk, from the aspect of data security, comes from:
(a) hackers working over the telephone lines
(b) other computer users
(c) maintenance staff
(d) burglars
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