Software Development Cycle Models Life An Effective Software

Software Development -Cycle Models Life

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 – e. Xtreme 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