Page 177 - DCAP507_SYSTEM_SOFTWARE

Unit 11: Programming Languages Concept (II)

"Decide which module you want; partition the program so that data is hidden in modules." Notes

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Caution To produce modular design, some criteria must be used to select modules so that
the module support well defined abstractions and are solvable and modifiable separately.
A program can be logically separated into the following functional module:
 Initialization

 Input
 Input data validation
 Processing
 Output
 Error handling

 Closing Procedure.
The modules reflect a logical flow for a computer program. After initialization, processing
proceeds logically with input, input validation, various processing modules and output. Error
handling may be required during execution of any modules.

11.1.1 Advantages of Modular Approach

 Testing of individual modules in isolation makes tracing errors easier.
 Modules can be kept separately in a library and used anywhere in the program without
rewriting them.
 A module can use other modules.
 The documentation of a large program is simplified by the documentation of individual
modules.
 We can develop modules, which contain standard procedures throughout the program,
thus saves development time.
A program consists of modules, which may have modules of their own: indeed a program is
hierarchy of modules. Almost all design contains hierarchies, as creating a hierarchy is a natural
way to manage complexity. Moreover the highest level modules correspond to the entire
program. The question arises at this time is, "In what order should the modules be built-starting
from the top level or starting from the Bottom level?" To design such hierarchies there are two
approaches: Top down and Bottom up.

11.1.2 Top-down Approach

A top-down design approach starts by identifying the major modules of the program i.e.
decomposing them into their lower level modules and iterating until the desired level of details
is achieved. First the main module is implemented and then their subroutines and so on. Top
down design method often results in some forms of stepwise refinement.
Starting from an abstract design, in each step the design is refined to a more concrete level until
we reach a level where no more refinement is required and the design can be implemented
directly.

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