What is stepwise refinement? Discuss partitioning & abstraction.

Stepwise Refinement:-Stepwise Refinement is a top-down design strategy originally proposed by Niklaus Wirth. A program is developed by successively refining levels of procedural detail. A hierarchy is developed by decomposing a macroscopic statement of function in a stepwise fashion until programming language statements are reached.

Refinement is actually a process of elaboration. We begin with a statement of function that is defined at a high level of abstraction. That is, the statement describes function or information conceptually but provides no information about the internal workings of the function or the internal structure of the information. Refinement causes the designer to elaborate on the original statement, providing more and more detail as each successive refinement occurs.

Partitioning:-Problems are often too large and complex to be understood as a whole. For this reason, we tend to partition such problems into parts that can be easily understood and establish interfaces between the parts so that overall function can be accomplished.

Partitioning decomposes a problem into its constituent parts. We establish a hierarchical representation of function or information and then partition the uppermost element by:-

1)     Exposing increasing detail by moving vertically in the hierarchy or

2)     Functionality decomposing the problem by moving horizontally in the hierarchy.

Abstraction:- Abstraction permits one to concentrate on a problem at some level of generalization without regard to irrelevant low level details; use of abstraction also permits one to work with concepts and terms that are familiar in the problem environment without having to transform them to an unfamiliar structure.

�      It allows considering the modules at the abstract level without worrying about its details.

�      It provides external behavior of the modules.

�      It is used for existing modules as well as for modules that are being design.

�      It is essential for the problem partitioning.