The document discusses several design techniques for software development including top-down design, bottom-up design, stepwise refinement, levels of abstraction, structured design, integrated top-down development, and Jackson structured programming. Top-down design starts by identifying major modules and decomposing them into lower level modules. Bottom-up design first identifies primitive objects, actions, and relationships. Stepwise refinement involves decomposing design decisions to elementary levels in small increments.

1. DESIGN TECHNIQUES

2. Design techniques are based on the “Top-down” or
“Bottom-up” strategies.
TOP-DOWN DESIGN:
A Top-down design approach starts by identifying the
major modules of the system, decomposing them into their lower level
modules and iterating until the desired level of detail is achieved.
BOTTOM-UP DESIGN:
In the bottom-up approach to software design, the
designer first attempt to identify a set of primitive objects, actions and
relationships that will provide a basis for problem solution.

3. STEPWISE REFINEMENT:
Stepwise refinement is a top-down design strategy
proposed by NIKLAWS WIRTH.
Stepwise refinement provides a general framework
for problem solving by placing emphasis on the importance of
proceeding from general concerns to specific details in small increment
steps.
The process of program refinement is analogous to
the process of refinement and partitioning that is used during
requirement analysis.
Stepwise refinement involves the following activities.
 Decomposing design decisions to elementary levels.
 Insolating design aspects that are not truly interdependent.
 Postponing decisions concerning representation details as long as
possible.
 Carefully demonstrating that each successive step in the refinement
process is a faithful expansion of previous steps.

4. LEVELS OF ABSTRACTION:
Levels of Abstraction is a bottom-by design
technique, in which operating system was designed as a layering of
hierarchical level starting at level 0 and building up to level of
processing independent user programs.
Each level of abstraction performs a step of services
for the functions on the next level of abstraction.
STRUCTURED DESIGN:
The primary goal of structured design is to divide a
problem into modules such that coupling between different modules is
reduced while the cohesion of different module is enhanced.
In structured design methodology , structure charts
represent the design. The structure of a program is made up of modules
of that program together with the inter connection between them.

5. A
B C D
There are some modules that obtain information from
their subordinates, and the pass it to their subordinates. This kind of
module is an input module. An out put module takes information from its
subordinates and passes it on to its subordinates.
INPUT MODULE OUTPUT MODULE

6. INTEGRATED TOP-DOWN DEVELOPMENT:
Integrated top-down development integrates
design, implementation and testing.
MAIN
GET PROCESS PUT
SUB1 SUB2

7. DESIGN MAIN
CODE MAIN
STUBS FOR GET,PROCESS,PUT
TEST MAIN
DESIGN GET
CODE GET
TEST MAIN,GET
DESIGN PROCESS
CODE PROCESS
STUBS FOR SUB1,SUB2
TEST MAIN,GET,PROCESS
DESIGN PUT
CODE PUT
TEST MAIN,GET,PROCESS,PUT
DESIGN SUB1
CODE SUB1
TEST MAIN,GET,PROCESS,PUT,SUB1
DESIGN SUB2
CODE SUB2
TEST MAIN,GET,PROCESS,PUT,SUB1,SUB2

8. JACKSON STRUCTURED PROGRAMING:
Jackson Structured Programming was developed by
Micale Jackson as a systematic technique for mapping the structure of a
problem into program structure of a problem to solve the problem.
The mapping is accomplished in three steps:
1. The problem is modeled by specifying input and output data structures
using tree structured diagram.
2. The input-output model is converted into a structural model for the
program by identifying points of correspondence between nodes in the
input and output trees.
3. The structure model of the program is expanded into a detailed design
model, that contains the operations needed to solve the problem.