Question 5

What is “model”?
What is “snowball effect”?
What is “waterfall diagram”?

Model is a representation of a something,generally in a smaller scale.Model shows the working of an object,a system or a concept.For example,before producing a car,model of the car is produced.The model shows the deficits of car and it can be revised.

Snowball effect is a figurative term comes from a small ball of snow that starts to become larger as it goes down from the top of mountain.Finally it becomes an avalance that has dangerous and destructive effect.Similiarly,a process starts with a small action,one action triggers another and the action chain becomes larger and larger in a beneficial way or in a harmful way.

Waterfall diagram comes from waterfalls.For waterfalls, 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. the waterfall model describes a development method that is linear and sequential. Waterfall development has distinct goals for each phase of development. 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 repeating steps.

references:
http://en.wikipedia.org/wiki/Model_%28abstract%29
http://en.wikipedia.org/wiki/Model
http://en.wikipedia.org/wiki/Snowball_effect
http://searchsoftwarequality.techtarget.com/sDefinition/0,,sid92_gci519580,00.html