5.2 Structured Design VS Object Design

Structured design was developed in 1970s to deal with complex information systems which have many different functions. Structured design uses structure chart as main primary modeling technique to provide guidance for deciding what set of programs should be, what each program should achieve and how each program should be organized in hierarchy.

Structured design describes functions and subfunctions of each part of system, it shows relationship between modules of a computer program uses two main concepts of coupling & cohesion to structure and organize modules. Detailed explanation of these modules are explained in the next posts.

Structured design assumes the designer knows what the system needs to do & what the main functions are, what are inputs and outputs therefore a key aspect of user-interface is done in conjunction with structured design especially after the database is used in the system and users have to interact with it.

The weakness of structured design is that it only addresses some but not all of the activities in analysis and design which makes it more like an art where people like more comprehensive & rigorous technique like engineering principles. Another weakness of structured design is the transition from DFD to structured chart didn’t work well on the other hand many believed that data modeling is more important than process modeling – in structured analysis & design process is centre of focus of system.

Object oriented approach views system as collection of interacting objects that work together to accomplish tasks therefore conceptually there is no data entities or files, no program or process. OO design defines all kinds of objects necessary for communication, showing how objects interact to complete tasks and refining definition of each object so it can be implemented with specific language or environment.

Two main important models used in OO design are design class diagram and interaction diagram. Class diagrams are developed for domain, view & data access layer. Interaction diagram extend system sequence diagram.

As said; in OO approach it's only objects and they send each other messages to collaborate and support functions of main program.

According to Rob (2004) :" The steps of developing a system (planning, analysis, design, implementation) do not change but how they are performed can be different."

In structured Approach we use DFD, in OO approach we use Use Cases. likewise; in structured approach design of system components i.e. input, output, modules of program and DB are evolved from DFD. In OO approach we use UML and there is no clear-cut step and no single model that components evlove from it.

In practice, organisations use combination of structured and OO approach however Rob (2004) believes that in the era of OO programing, OO modeling and OO design is desired and mixing up structured methodology & OO methodology can be confusing. He believes we need clear definition of models and steps as an analyst moves from the activities of analysis to design to implementation.

REFERENCES:

* Systems Anslysis And Design in a Changing World - SJB

* Rob Mohammad A., (2004). "Issues of Structured VS. Object-Oriented Methodology of System Analysis and Design". University of Houston-Clear Lake.