when we enter a value in module a is entry criteria and to 
check whether the value has present in module b is called 
exit criteria for integration . Here we r checking the flow 
from module to module .

It describes the flow of your project. In entry criteria we 
define what is the initial need of the project. Suppose in 
the first step of the project a file have to import that 
contains a specific data then for this project this files 
comes under Entry criteria.
IO Exit criteria we cover all the things which should be 
the output of the last step suppose generation of any file 
or any situatiion.

Thanks
Vishal

entry criteria of integration : is like checking the
availability of data that is to be shared or not.

exit criteria of integration: is like checking that the
shared data is available in dependent module or not.

example: if we posted data in a module named "a" and that
must be visible in module "b","c","d" now we will check the
availability of the data that has to be shared and we will
go for module "b" and check that the data that is present in
module "a" is available or not.

Entry level criteria is that CDD is ready and exit level 
criteria is that the communication flow and data flow 
should be satisfied.