SAD-Design Methodologies

Design methodologies aim at the following
  •  Improve productivity of the analysts and programmers.
  •  Improve documentation.
  •  Cut down costs.
  •  Improve communication among users, analysts, designers and the programmers.
  •  Simplify the design by segmentation.

Structured design is a data flow based methodology. This design partitions a program into small, independent modules. They are arranged in a hierarchy called a top down manner. This method minimizes complexity and makes a problem manageable by subdividing it into smaller segments. This approach is called modularization or decomposition.

Design is said to be top down if it consists of a hierarchy of modules, with each module having a single entry and single exit subroutine. The primary advantage of this sign

1.critical interfaces are tested first
2.Early versions of the design, though incomplete, are useful enough to resemble the real system.
3.Structuring the design provides control and improves morale
4.The procedural characteristics define the order that determines processing.

The documentation tool for structured design is the hierarchy or structured chart. It is a graphical tool for representing hierarchy, and it has three elements.

1. Module

1. The module is represented by a rectangle with a name. It is a contiguous set of statements.
2.The connection is represented by a vector linking two modules. It means one module has called another module

In the above ex the module A calls the module B and it also calls the module C .
3.The couple is represented by an arrow with a circular tail. It represents data items moved from one module to another


HIPO is a forms-driven technique. Here standard documents are used to document the information. It consists of a hierarchy chart and an associated set of input/process/output charts. HIPO uses top-down decomposition. It describes the data input and output from processes and defines the data flow composition. The objectives are
  1. Provide a structure by which the functions of a system can be understood.
  2. State the functions to be performed by the program rather than specifying the program statements to be used to perform the functions.
  3. Provide a visual description of input to be used and output to be produced for each level of the diagram. 
HIPO makes the transformation of input to output data visible.

HIPO uses easy to draw symbols. The procedure to construct the HIPO chart is as follows
  1. Begin at the highest level of abstraction.
  2. Identify the processing steps that convert the input to the output.
  3. Document each element using the HIPO diagram notation and a treelike structure.
  4. Identify sub processes and their inputs and outputs. Continue decomposition until the processes cannot be decomposed further.

There are two tools used for drawing the HIPO diagrams
  • HIPO Worksheet ,GX20-1970
  • HIPO template , GX20- 1971

The template contains the symbols for the HIPO diagrams. HIPO format consist of 
Visual table of contents shows the structure of the diagram and the relationships of the functions in a hierarchical manner. It also has a legend to show how symbols are to be used. 
Overview diagrams describe the major functions and reference the major details diagrams needed to expand the functions adequately. They provide the following

a) The input section that contains the data items used by the process steps.
b) The output section that contains the data items created by the process steps.
c) Process section that contains numbered steps that describe the functions to be performed. Arrows connect then to the output steps and input/output data items.
d) The extended description refers to non-HIPO documentation and code

Detail diagram contains an extended description section that amplifies the process steps and references the code associated with each process steps.


An activity of all the phases of a structured project is a walkthrough. It is an interchange of ideas to agree on the validity of a proposed solution to a problem. The purpose of the design walkthrough is to anticipate as many problems as possible because it is cheaper to make changes in the design phase rather than in during conversion. The objective is to give a maintainable design that is flexible and adaptable.

User Involvement: Walkthroughs are held to review the system test plan, program design and production acceptance. In each case user has to be involved. The amount of success depends on the amount of use involvement.
  •  User involvement gives the designer feedback.
  •  It provides the basic understanding of what a candidate system will do and what it will not.
  •  It paves a way for user acceptance.
It bridges the gap between the designer and the user

In the above ex P and Q are couples. Module A calls B passing P downwards. Likewise, module A calls C passing Q downwards .
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