Describe Structured Analysis and Design Approach

 The goal of structured system analysis and design is to reduce maintenance time and

effort. Modeling is the act of drawing one or more graphical representations of a
System. Model driven development techniques emphasize the drawing of models to
help visualize and analyze problems, define business requirements and design
Information systems. The first model driven approach is Structured Analysis and
Design approach.

Structured Analysis is a development method for the analysis of existing manual
systems or automated systems, leading to development of specifications (expected
functionality or behavior) for proposed system. The objective of structured analysis
approach is to organize the tasks associated with requirement determination to provide
an accurate and complete understanding of a current situation. The major tasks of
structured system analysis approach are:

• Preliminary Investigation
• Problem Analysis
• Requirement Analysis
• Decision Analysis.

It is a process-centered technique that is used to model business requirements for a
system. Structured analysis introduced a process-modeling tool called the Data flow
diagram, used to illustrate business process requirements. With the help of DFD, the
systems analyst can show the system overview. Data modeling tools such as Entity
relationship diagrams are used to illustrate business data requirements. With the help
of ERD, the analyst, can show database overview.

Structured Design utilizes graphic description (Output of system analysis) and
focuses on development of software specifications. The goal of structured design is to
lead to development of programs consisting of functionally independent modules that
perform relatively independently of one another. It is a specific program design
technique, not a comprehensive design method. Thus it does not specify file or
database design, input or output layout or the hardware on which the application will
run. It provides specification of program modules that are functionally independent.

It is a process-centred technique that transforms the structured analysis models into
good software design models. Structured Design introduced a modeling tool called
Structure Charts. They are used to illustrate software (program) structure to fulfil
business requirements. Structure charts describe the interaction between independent
module and the data passing between the modules. These module specifications can
be passed to programmers prior to the writing of program code. In structure chart the
whole application is divided into modules (set of program instructions) and modules
are designed according to some principles of design. These principles are:

Modularity and partitioning: Each system should consist of a hierarchy of modules.
Lower level modules are generally smaller in scope and size compared to higher level
modules. They serve to partition processes into separate functions.

Coupling: Modules should be loosely coupled. It means that modules should have
little dependence on other modules in a system.

Cohesion: Modules should be highly cohesive. It means that modules should carry out
a single processing function.

Span of control: Modules should interact with and manage the functions of a limited
number of lower level modules. It means that the number of called modules should be
limited (in a calling module).

Size of Module: The number of instructions contained in a module should be limited
so that module size is generally small.

Shared use of Functions: Functions should not be duplicated in separate modules
may be shared. It means that functions can be written in a single module and it can be
invoked by any other module