5 : System Development Life Cycle MODELS - Part 1

System Development Life Cycle MODELS

We will discuss 5 different types of SDLC models prevalent in the industry.

Waterfall

Incremental

Spiral

RAD

V model

What is a waterfall?

 Waterfall Model

The waterfall model is a sequential software development model in which development is seen as flowing steadily downwards (like a waterfall). To follow the waterfall model, one proceeds from one phase to the next in a purely sequential manner.

Thus the waterfall model maintains that one should move to a phase only when its preceding phase is completed and perfected. Simple, Phases of development in the waterfall model are discrete, and there is no jumping back and forth or overlap between them.

Usage

The Waterfall model is widely used, including by such large software development houses as those employed by the U.S. Department of Defense and NASA.

Advantages of the waterfall model:

1. Fixed Requirement.
2. Emphasis on documentation
3. Structured approach, liner so easy to understand
4. If there is no rework then the model builds a high quality product.

Disadvantages of the waterfall model:

1. Long duration so requirements may change, acceptability of the product reduces.
2. If clients change their requirements after designing is finished, that will affect the overall budget of the project.
3. Testing is postponed to the later stage till coding is completed. So issues will be uncovered later.
4. Real projects rarely flow in the sequential flow.
5. No adaptability/flexibility in the project.
6. Working model is not seen till later stages.


Incremental Model

100 requirements and 60 core requirements in first phase.
20 in next phase
20 in next phase
20 in last phase

The incremental model combines elements of the linear sequential model with the iterative philosophy of prototyping. The incremental model applies linear sequences in a staggered fashion as calendar time progresses. Each linear sequence produces a deliverable “increment” of the software. More realistic approach.

For example , word-processing software developed using the incremental paradigm might deliver basic file management, editing, and document production functions in the first increment; more sophisticated editing and document production capabilities in the second increment; spelling and grammar checking in the third increment; and advanced page layout capability in the fourth increment.

When an incremental model is used, the first increment is often a core product.

That is, basic requirements are addressed, but many supplementary features (some known, others unknown) remain undelivered.

Incremental development is the process of establishing requirements, designing, building and testing a system done as a series of smaller developments.

Advantages

1. More realistic approach to development of large scale systems and software.
2. Each increment is fully tested before beginning the next.

Drawbacks

1. Total planned testing effort would be more than that for waterfall model.