Design Module view What module should the system and which have to be developed . It determines the module structure of components.

Coupling It is the measure of the degree of interdependence between modules. Coupling between the modules is the strength of interconnection between modules or a measure of interdependence among modules. Highly coupled – strong interconnection Loosely coupled- weak interconnection

Factors Affecting Coupling Number of interfaces increases coupling. Complexity of interface Type of info flow along interfaces Data control

Types of coupling Data coupling: The dependency b/w module A and B is said to be data coupled if their dependency is based on the fact they communicate by only passing of data. Stamp Coupling: When complete data structure is passed from one module to another. Control Coupling: Passing of control information. This is set by flags that are set by one module and reacted upon by the dependent module.

Common Coupling: Module A and B have share data. External coupling: Related to the communication external tools and devices. Common Coupling: Module A and B have share data. Content Coupling: Module A changes data of module B. A B C D

Cohesion Cohesion is a measure of a degree to which the elements of a module are functionally related. Cohesion of the module represents how tightly bound the internal elements of the module are to one another

Levels / Types of cohesion Coincidental: X and Y here no conceptual relation ship other than shared code. Logical: X and Y performs logically similar operations. Temporal : Tasks that are related by the fact that all tasks must be executed in the same time span.

Procedural: Procedural cohesion occurs in modules whose instructions although accomplish different tasks yet have been combined because there is a specific order in which the tasks are to be completed. Communicational: X and Y both operate on same input/ output data. Sequential: X outputs some data which forms input to Y. Functional: X and Y are a part of single functional task. Related to performing single function.

Functional oriented design The design process for software systems often has two levels. At first level the focus is on deciding which modules are needed for the system, their specification of these modules, and the modules should be interconnected. Design is imposed on a set of interacting units where each unit has clearly defined functions.

This method works fine for small programs. While(not finished) { Read an expression; Evaluate the expression; Print the value; }

Print module Print (expression exp) { Switch(exp->type) Case integer Print integer; Case real Print real; }

Top down structure

Functional oriented design are represented as DFD Data Dictionary Structure chart Pseudo code Structure chart is one of the most commonly used method for system design. Black boxes are used.

Data Control Module Conditional call of module

Pseudocode Using Pseudocode, the designer describes system characteristics using short concise , english language phrases that are structured by keywords such as If then Else, Do while, end .

Relation Ship b/w cohesion and Coupling A s/w engg must design the modules with goal of high cohesion and low coupling.