UNIT-II Software Requirement Analysis And Specification: Need for SRS, Problem Analysis, Requirements Specification. Software Design: Design objectives and principles. Module level concepts, Coupling and Cohesion. Design Notations and specifications.
Structured Design Methodology, Object Oriented Design. Detailed Design: Detailed Design, Verification (Design Walkthroughs, Critical Design Review, Consistency Checkers), Metrics.
Modularity is the single attribute of software that allows a program to be intellectually manageable. It enhances design clarity, which in turn eases implementation, debugging, testing, documenting, and maintenance of software product.
This can be achieved as:
✓Controlling the number of parameters passed amongst modules.
✓ Avoid passing undesired data to calling module.
✓ Maintain parent / child relationship between calling
& called modules.
✓ Pass data, not the control information.
Coupling
✓ The degree of interdependence between two modules”
✓ We aim to minimise coupling - to make modules as independent as possible.
Low coupling can be achieve by:
✓ eliminating unnecessary relationships
✓ reducing the number of necessary relationships
✓ easing the ‘tightness’ of necessary relationships
Given two procedures A & B, we can identify number of ways in which they can be coupled.
1, Data Coupling : The dependency between 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. Other than communicating through data, the two modules are independent.
✓ Modules communicate by parameters
✓ Each parameter is an elementary piece of data
✓ Each parameter is necessary to the communication
✓ Nothing extra is needed.
2. Stamp coupling: Stamp coupling occurs between module A and B when complete data structure is passed from one module to another.
✓ A composite data is passed between modules
✓ Internal structure contains data not used
✓ Bundling - grouping of unrelated data into an artificial structure
3. Control coupling
Module A and B are said to be control coupled if they communicate by passing of control information. This is usually accomplished by means of flags that are set by one module and reacted upon by the dependent module.
✓ A module controls the logic of another module through the parameter.
✓ Controlling module needs to know how the other module works.
4. Common coupling
A form of coupling in which multiple modules share the same global data. Global data areas are commonly found in programming languages.
Making a change to the common data means tracing back to all the modules which access that data to evaluate the effect of changes.
✓ Use of global data as communication between modules
• So common coupling has got disadvantages like
difficulty in reusing modules, reduced ability to control data accesses and reduced maintainability.
5. Content coupling
In a content coupling, one module can modify the data of another module or control flow is passed from one module to the other module. This is the worst form of coupling and should be avoided.
When a module can directly access or modify or refer to the content of another module, it is called content level coupling. One module directly references contents of the other.
1. Example of Content Coupling Part of program handles lookup for customer. When customer not found, component adds customer by directly modifying the contents of the data structure containing customer data.
2. Example of Content Coupling Occurs when one component modifies an internal data item in another component, or when one component branches into the middle of another component.
✓ A module refers to the inside of another module
✓ Branch into another module
✓ Refers to data within another module
✓ Changes the internal workings of another module
✓ Mostly by low-level languages
