Sunday, February 17, 2013

Module specification


Module Specification
Module is the way to improve the structure design by break down the problem for solving it into independent task.

Advantages of Module –
                               I.            It breakdown the problem into independent modules so the complexity of the problem can be minimized.
                             II.            Each independent module can be easily assigned to the various members of the development team.
                          III.            Module can be easily run and tested independently from another.

Top-Down design approach:-
It is a technique of breakdown a problem into major tasks to be performed. Each task is then further broken down into separate sub task and so on until each sub task is sufficiently simple to be written as a self contained module.
            In Top-Down design we initially describes the problem at the highest level that descript what must be done and It does not show how it must be done. Top-Down methods are used throughout the system analysis and design process. The value of using top-down approach, starting at general level and to understand and gain the system and moving down to the levels of greater details.

Advantages of Top-Down Approach –
                               I.            By dividing of the problem into number of sub problems we have made it easier to share problem development.
                             II.            It is easy to debug a large program as a number of smaller units rather than one big problem.
                          III.            It is good way to delay decision on problems whose solution is not readily prepared.
                          IV.            It allows a programmer to remain on top of a problem and view the developing solutions. The solution always proceeds from the highest level to the lowest level.
                            V.            It becomes an ideal structure for managing the implementation of a computer program using team of programmers.

Bottom-Up design approach:-
When we face a large and complex problem , it is difficult to see how the whole thing can be done so it may easier to solve the part of the problem individual, taking the common and easy aspects first and then more difficult task and finally gather them all together to form complete solution, this is called bottom-up approach.
            The bottom-up approach suffers from disadvantage that the part of the program may not fit together very easily and there may be a lack of consistency between modules and reprogramming have to be done.

Module Cohesion & Coupling:-
                           i.)            Modules:
Module is represented by a rectangle box with module name. After defining general purpose of each program it is divided into modules. Each of which performs a single function.
For Ex:-
            An accounting system consists of many separate modules that are invoked one at a time as user wish to perform particular function. Each upper level module leads to using one or more lower level modules until the desired function is performed.

                         ii.)            Connectors:
Connections between modules are represented using links, modules. It is drown by on arrow line in downward direction.

                      iii.)            Coupling:
It refers to the strength of relationship between modules in the system. Coupling measures the degree to which two distinct modules are bound together.
It can be of two types –
a)     Data Coupling:
It carries data between two modules and it can have upward or downward direction. Data flows are shown using named arrow with a small circle at one end. It is shown by an arrow with blank circle at the tail.


b)    Control Coupling:
It carries info about data couple and does not carry any data. It is shown by an arrow with filled circle at the tail.



                      iv.)            Cohesion:
It is used to denote the intra module strength. It is a relationship among elements within a module. A system designer should aim at minimizing coupling and maximizing cohesion to get modular design. Designer insures that each module performs a specific function and can be developed independently. A good design has low coupling i.e. low interdependence between modules and high cohesion i.e. high interrelationship within the elements of a single module.
            Using Top-Down approach to plan the software for a system is no guarantee that errors will be avoided totally so properly modularized, cohesive system, the contents of the module are designed such that they perform a specific function and easily understood by people.

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