FUNCTION ORIENTED DESIGN

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FUNCTION ORIENTED DESIGN

The design activity begins when an SRS document to be developed if available.

The design process s/w s/m has two levels.

At the first level, the focus is on deciding which modules are needed for the s/m.

The specification of these modules and how the modules should be inter connected.

Function oriented design is an approach to s/w design where the design is decomposed into a set of interacting units where each unit has a clearly defined function.

This s/m is designed from a functional new point.

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DESIGN NOTATIONS

During the design phase there are two things of interest.

The design of the s/m and the process of designing itself.

Design notations are largely meant to be used during the process of the design and are used to represent design or design decisions.

For a function oriented design,the design can be represented graphically or mathematically by the following:

DATA FLOW DIAGRAM (DFD)

DATA DIRECTORIES

STRUCTURE CHARTS

PSEUDO CODE

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DATA FLOW DIAGRAM

Data flow diagrams are widely used for modeling the requirements.

They have been used for many years for representing various systems.

DFD shows the flow of data through a s/m.

The s/m may be a company,an organization or a set of procedures.

The DFD is also known as data flow graph or bubble chart.

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DATA DIRECTORIES

Families of DFD's can become complex.

To overcome this complexity is to draw DFD with data directories.

data directories are simply repositories to store information about all data items defined as DFD's.

Typical information stored in DFD's include:

Name of the data item

Aliases

Description or purpose

Range of values

Data structure definition

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STRUCTURE CHART

Structure chart is one of the most commonly used method for designing the s/m.

It partition the s/m into black boxes.

A black box means that functionality is known to the user without having the knowledge of internal design.

Inputs are given to the black box and appropriate outputs are generated by the black box.

This concept reduces the complexity bcoz details are hidden from those who doesn't need to know or desire to know.

Thus,systems are easy to construct and easy to maintain.

In a structure chart each program module is represented by a rectangular box.

Modules at the top level calls the modules of lower level.

The connection btw the modules are represented by lines btw the rectangular boxes.

The components are generally read from top to bottom or left to right.

Modules are numbered in hierarchical numbering scheme.

When a module calls another ,it views the called module as a black box,passing parameters for the called module,functionality and Receiving answers.

Control data passed btw modules in a structure chart is represented by a labelled directed arrow with filled in circle and data is depicted with an open circle.

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PSEUDO CODE

Pseudo code notation can be used in both the preliminary and detailed design phase.

Like flow charts pseudo code can be used at any desired level of abstraction.

Using pseudo code,the designer describes the s/m characteristics using short,concise,English phrase,data structures by keywords such as if-then-else,while-do and end.

Keywords and indentations describes the flow of control.

While the English phrase describes the processing action.