| 3. |
(a) Define what is
meant by Information Hiding. |
[2] |
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Modules
should be designed so that information contained within a module is inaccessible to
modules that have no need for such information. |
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[2
marks] |
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(b) In design history, modularity
can be thought of as a method of managing complex program by sub-dividing them into
distinct and manageable parts. In the study of design however, there is also an issue of cost.
Explain, with the aid of an appropriate diagram, the conflicting nature of cost and
modularity: why might it not be always a good idea to have a very high degree of
modularity? In your answer, indicate what you feel is a possible solution to these two
factors. |
[5] |
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2 marks for
correctly labelled diagram: |
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3 marks for
explanation, which should cover the following points: |
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Cost/effort and number
of modules are 2 conflicting factors: as number of modules increases, cost per module
decreases, but cost to interface increases |
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Explain and identify
the region of minimum cost |
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Explain the 'ideal'
point: the intersection between the cost per module and the cost to the interface curves |
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[5
marks] |
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(c) Cohesion and
Coupling are two ways of measuring the degree of modularity. Define what is meant by both
terms, and then indicate the degree desirable for each. |
[3] |
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Coupling measures the
degree of interdependence between two modules |
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Cohesion measures the
strength of functional association between elements within a module |
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Desirable to have low
coupling and high cohesion |
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[1 mark for
each point] |
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[3
marks] |
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(d) After the design
step in a life-cycle usually comes the coding step. There are several factors that should
be considered when choosing a suitable programming language for the coding step, one of
which might be the algorithm and computational complexity of the program. Identify, and
then describe in your own words, any five other such factors. |
[1] |
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Other
possible factors are: |
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General application
area |
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Environment in which
software will execute |
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Performance
considerations |
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Data structure
complexity |
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Knowledge of software
development staff |
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Availability of a good
compiler or cross-compiler |
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For each
factor, 1 mark for identification and 1 mark for explanation |
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[10
marks] |
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