Software Development Lifecycles - Sequential Lifecycle Models

The software development lifecycle begins with the identification of a requirement for software and ends with the formal verification of the developed software against that requirement. Traditionally, the models used for the software development lifecycle have been sequential, with the development progressing through a number of well defined phases. The sequential phases are usually represented by a V or waterfall diagram. These models are respectively called a V lifecycle model and a waterfall lifecycle model.


There are in fact many variations of V and waterfall lifecycle models, introducing different phases to the lifecycle and creating different boundaries between phases. The following set of lifecycle phases fits in with the practices of most professional software developers.

· The Requirements phase, in which the requirements for the software are gathered and analyzed, to produce a complete and unambiguous specification of what the software is required to do.

· The Architectural Design phase, where a software architecture for the implementation of the requirements is designed and specified, identifying the components within the software and the relationships between the components.



· The Detailed Design phase, where the detailed implementation of each component is specified.
· The Code and Unit Test phase, in which each component of the software is coded and tested to verify that it faithfully implements the detailed design.
· The Software Integration phase, in which progressively larger groups of tested software components are integrated and tested until the software works as a whole.
· The System Integration phase, in which the software is integrated to the overall product and tested.
· The Acceptance Testing phase, where tests are applied and witnessed to validate that the software faithfully implements the specified requirements.

Software specifications will be products of the first three phases of this lifecycle model. The remaining four phases all involve testing the software at various levels, requiring test specifications against which the testing will be conducted as an input to each of these phases.

Software Testing & Software Development Lifecycles

The various activities which are undertaken when developing software are commonly modelled as a software development lifecycle. The software development lifecycle begins with the identification of a requirement for software and ends with the formal verification of the developed software against that requirement.

The software development lifecycle does not exist by itself, it is in fact part of an overall product lifecycle. Within the product lifecycle, software will undergo maintenance to correct errors and to comply with changes to requirements. The simplest overall form is where the product is just software, but it can become much more complicated, with multiple software developments each forming part of an overall system to comprise a product.

There are a number of different models for software development lifecycles. One thing which all models have in common, is that at some point in the lifecycle, software has to be tested. This paper outlines some of the more commonly used software development lifecycles, with particular emphasis on the testing activities in each model.

The models under consideration here are:

• Sequential Lifecycle Model - V Lifecycle Model & Waterfall Lifecycle Model
• Progressive Development Lifecycle Model
• Iterative Lifecycle Model

Let's have a brief look at all of these models...