a)	Spiracle model is nothing but version by version 
model
b)	That is 1st version when completed after the hear 
UAT is done after go to the next version or build
c)	This is very risk modal according to application 
developments companies.
d)	The project have so many risks 
e)	And Client requirements also be changes 
continuously in the project
f)	Picture is not necessarily

My name is k.chandra sekhar,
My phone no is 09246540049,
Hyderabad.
My mail id is ndra_143@yahoo.co.in 
If any body want full explain send that mail

Whenever the requirement is not stable and cannot to freeze 
the requirement, Spiral model will be followed.

picture
 
   requirement  ---> design ---->code ----> implementation
Then it stats from the requirement. ie, whenever the 
requirement is coming the flow will start from requirement 
phase to the implementation phase.

      

spiral model was developed by Garry boehm.It combines the 
systematic aspects of the water fallmodel & itertative 
nature of the prototyping model.It is used for the projects 
which involves greater risk.