Software Development Life-Cycle Models

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

The Waterfall Model Requirements Analysis Software Design Coding Testing Maintenance

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)

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

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

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

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

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

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

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

The Spiral Model Planning Risk Analysis Development Evaluation

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

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

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

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)

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

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

“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)

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