In this section we will discuss various models for Software Testing. Definitions of these models will differ. However, the fundamental principles are agreed on by experts and practitioners alike. There are many models used to describe the sequence of activities that make a Systems Development Life Cycle (SDLC). SLDC is used to describe activities of both development and maintenance work in Software Testing.
These models would give benefit if given attention as earlier as possible to all the testing activity that has to be done at some time during the SDLC in Software Testing.
Any reasonable model for SDLC must allow for change and spiral approach allows for this with emphasis on slowly changing (evolving) design. We have to assume change is inevitable and will have to design for change, which means every design should be ready to accommodate future changes.