1. Software Development Life-Cycle Models

2. An Effective Software Development Process
Is written down
Is followed
Is actively managed
The process is dynamic
Its effectiveness is measured regularly
Measurement results are used to improve the process

3. The Waterfall Model Requirements Analysis Software Design Coding
Testing
Maintenance

4. Advantages of the Waterfall Model
Easy to understand
Widely used
Reinforces notions of “define before design” and “design before code”
Establishes milestones (when deliverables are produced and when reviews take place)

5. Disadvantages of the Waterfall Model
Not realistic (doesn’t match real projects)
Does not reflect the iterative nature of software
Complete set requirements seldom known at the beginning of a project
Working software not available until near end of project
Does not incorporate risk assessment

6. The Concurrent Development Model
Development and QA/Testing are performed concurrently
Similar to the Synchronize and Stabilize model used by Microsoft
Multiple baselines are included as part of the process
SRS evolves over the course of the project
Ends with a formal validation phase with defined criteria for starting and stopping

7. Advantages of the Concurrent Development Model
It’s flexible – the number incremental releases can be determined by the project team
Immediate feedback from testing
New features can be added late in the project
No surprises during formal validation because testing has been continuous

8. Disadvantages of the Concurrent Development Model
The SRS must be continually updated to reflect changes
It requires discipline to avoid adding too many new features too late in the project

9. The Rapid Prototyping Model
Requirements gathering
Quick design
Prototype building
Prototype evaluation by customers
Prototype may be refined
Prototype thrown away and software developed using formal process

10. Advantages of the Rapid Prototyping Model
Users/customers own requirements
Instills customer confidence that the “right” product is being built
Provides a good way to determine requirements when there is uncertainty about what is needed

11. Disadvantages of the Rapid Prototyping Model
Prototypes are not always thrown away – they often become the products or fundamental parts of the products
Requires lots of customer involvement which isn’t always possible
Validation may be difficult because the requirements may not be well documented

12. The Spiral Model
Planning
Risk Analysis
Development
Evaluation

13. Advantages of the Spiral Model
Incorporates the iterative nature of software development
Incorporates all the advantages of both the waterfall model and prototyping model

14. Disadvantages of the Spiral Model
Requires expertise in risk analysis
It is somewhat complicated and not well understood

15. Hybrid Models Combined aspects of two or more models Added flexibility
Not usually well understood
Have all advantages and disadvantages of the models encompassed

16. Object-Oriented Models
Requirements analysis and design tend to be blurred
Tend to be iterative in nature
Usually incorporate risk management
Incorporate requirements management and change control
Emphasize the use of visual models (e.g. UML diagrams)

17. Models Based on Agile Methods
ASD – Adaptive Software Development
Crystal
TDD –Test-Driven Development
DSDM – Dynamic Systems Development Method
Lean Software Development
Scrum
XP – eXtreme Programming

18. Agile Methods Emphasize
Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan

19. “How to Solve It”
In 1945 George Polya wrote a book outlining 4 basic steps in problem solving:
Understand the problem (requirements analysis)
Devise a plan (software design and project planning)
Carry out the plan (coding)
Look back (testing the solution)

20. Summary Choosing the right life-cycle model can be difficult
But it is essential to have one
The life-cycle model covers more than just development – it must be appropriate for product support and maintenance