Question

Coupling and cohesion are design concepts that software engineers must consider seriously during software development:

1. Which type of coupling would you consider to be most desirable. Give reasons      [6]
2. Which type of cohesion would you consider to be most desirable. Give reasons      [6]
3. Define software reuse and explain its benefits in software development                  [8]

Question three

Explain how COCOMO is used in software development                                         [10]

Answer 1

a. Most desirable form of coupling is Data Coupling.

Reason: 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.

b. Most desirable form of cohesion is Functional Cohesion.

Reason: Functional Cohesion is a type of cohesion in which the tasks performed by a software module all contribute to the performance of a single function.

c. Software reuse is the process of creating software systems from predefined software components.

• Benefits of software reuse:
  • Increase software productivity.
  • Shorten software development time.
  • Improve software system interoperability.
  • Develop software with fewer people.
  • Move personnel more easily from project to project.
  • Reduce software development and maintenance costs.
  • Produce more standardized software.
  • Produce better quality software and provide a powerful competitive advantage.

d. COCOMO Model

This is a cost estimation model in software in software engineering and it allows you to input some parameters and get an estimate of the level of effort associated with a software project.

The initial version was published in 1981 and was known as COCOMO-81. It was developed considering a waterfall process would be used and that all software will be developed from scratch. The COCOMO model is one of the most popular models cost estimating in software engineering domain.

Model 1: The Basic COCOMO Model

If the function of program size can be expressed as estimated LOC (Source Lines of code – SLOC, KLOC) then it can be computed as software development effort.

COCOMO applies to three classes of software projects:

• Organic Mode Mode: It is related to projects with small development teams whose team members are familiar with the project. Eg. Payroll Systems
• Semi-Detached Mode: It is related to the projects that involve the mixture of experienced team members in the project. E.g. Interactive Banking System
• Embedded Mode: It is related to the complex projects that are developed under tight constraints with innovations in it having a high volatility of requirements. E.g. Nuclear Reactor Control Systems.

Model 2: The Intermediate COCOMO Model

If program size includes a set of “cost drivers” with personnel and project attributes, subjective assessments of products and hardware then it can be computed as software development effort. This extension includes a set of four cost drivers.

• Product attributes
• Hardware attributes
• Personnel attributes
• Project attributes

Model 3: The Advanced COCOMO Model:

Along with characteristics of an intermediate model this model also assesses the cost driver’s impact on each step of the software engineering process. There are a total of 6 phases of detailed COCOMO.

• Planning and requirements
• System design
• Detailed design
• Module code and test
• Integration and test
• Cost Constructive model