What's Waterfall Model?

The waterfall model is a popular version of the SDLC(systems development life cycle model) for software engineering. Often considered the classic approach to the systems development life cycle, the waterfall model describes a development method that is linear and sequential. Waterfall development has distinct goals for each phase of development. Imagine a waterfall on the cliff of a steep mountain. Once the water has flowed over the edge of the cliff and has begun its journey down the side of the mountain, it cannot turn back. It is the same with waterfall development. Once a phase of development is completed, the development proceeds to the next phase and there is no turning back.
The advantage of waterfall development is that it allows for departmentalization and managerial control. A schedule can be set with deadlines for each stage of development and a product can proceed through the development process like a car in a carwash, and theoretically, be delivered on time. Development moves from concept, through design, implementation, testing, installation, troubleshooting, and ends up at operation and maintenance. Each phase of development proceeds in strict order, without any overlapping or iterative steps.
The disadvantage of waterfall development is that it does not allow for much reflection or revision. Once an application is in the testing stage, it is very difficult to go back and change something that was not well-thought out in the concept stage. Alternatives to the waterfall model include joint application development(JAD), rapid application development (RAD), synch and stabilize, build and fix, and the spiral model.

Example of SDLC in waterfall model

Let's see. What's activity network diagram?

An Activity Network Diagram will help you to work out the most efficient sequence of events needed to complete any project. It enables you to create a realistic project schedule by graphically showing

• the total amount of time needed to complete the project
• the sequence in which tasks must be carried out
• which tasks can be carried out at the same time
• which are the critical tasks that you need to keep an eye on.

How to do it:

1. Beginning with the first task until last tasks. This is called the forward pass.

For example:

• Previous task numbers 1 to 7 =====> 11 days
• Earliest start for task number 8 ===> 11^th day
• Task number 8 takes ===========> 3 days
• Earliest start for task number 9 ===> 14^th day

Write the LS on the job card.

2. Starting at the last task, calculate the latest time each task could be started and still finish. This is called the backward pass.

Example:

• Total implementation time =======> 60 days
• Last task (number 22) takes ======> 5 days
• Latest start for task number 22 ===> 55^th day
• Task number 21 takes ==========> 2 days
• Latest start for task number 21 ===> 53^th day

Write the LS on the job card.

3. When you have worked your way through every task on the diagram in this way you will notice that some tasks' earliest start times will be one or more days previous to their latest start times. There is no schedule flexibility for these tasks.

4. You can now schedule the dates for your final plan.

sample of activity network diagram