a)	When the customer or client requirements clear then 
that time use the waterfall model
g)	Spiracle model is nothing but version by version 
model
h)	The project have so many risks then
i)	Client requirements changes continuous then use 
this project


My name is k.chandra sekhar,
My phone no are 9246540049 65880049, Hyderabad.
My mail id is ndra_143@yahoo.co.in 
I am taking the class for projects and interview trips if 
you interest contact

- This is very simple model.  It moves like water fall from 
top to down of SDLC.  The drawback of this model is 
ineffectiveness of verification and validation activities.

Another name of water fall model:-Linear Sequential Model.

The difference b/w Waterfall and Sprial Model are:
1) Risk factor is considered in the Spiral Model but in 
water fall Model it is not considered.
2)In waterfall the requirements are freezed but this not 
happens in the Spiral Model.
3)Water fall Model is linear sequential model where sprial 
model works in loop.
4) Spiral Model is costely as Risk factor is covered.

the difference between waterfall and spiral model are:
1)waterfall model is simple and sequential,but spiral model
is complex.
2)waterfall works in sequential flow,but spiral works in loop.
3)In spiral model there is a better communication between
developer and customer,but in waterfall model the customer
should have patience.

waterfall model is a rigid model and can easily be 
manageble but spiral model is not

waterfall model works well on smaller projects whereas 
spiral model woks on larger projects also

waterfall model is a iterative process whereas spiral model 
is a partitioned in four quadrants it is also called meta 
model.

Waterfall Model:
-Series of stages carried out in sequence
-Products of each stage subject to QA inspections
-Only if the products are acceptable is the stage signed off
and the next allowed to start
-Each new stage starts from an agreed baseline established
at preceding stage
-In reality stages will overlap
-No stage is repeated unless a radical change of project scope
-Waterfall may provide a good starting point for structuring
the project
-Can be useful for inexperienced practitioners
Easy to build a simple plan around

Spiral Model:

-When requirements are not well known in advance spiral
model may provide an alternative
-An iterative approach to developing a system
--High level requirement specification is drawn up
--Tested by building a prototype solution
--Prototype is reviewed and requirements are clarified or
changed and amended requirements specification is issued
-The cycle is repeated until requirements are stable and
users approve the deign
-At the beginning of the spiral the focus is on requirements
issues 
-At the end concentrates with technical issues 
-Iterations can spiral out of control if not tightly managed
--Each iteration will lead to requests for change
--Difficult to call a halt to the process resulting in
projects running late and over budget
-Scope can be difficult to manage
-Final solution can be inadequately documented and poorly
structured
--Prototypes can be viewed as tool for capturing
requirements eliminating design stage
-Can lead to false user expectations
-Early prototypes raise expectations that final solution is
imminent