Data flow testing: Testing in which test cases are designed 
based on variable usage within the code.

This comes under White Box Testing. Data-flow testing looks 
at the lifecycle of a particular piece of data (i.e. a 
variable) in an application. By looking for patterns of 
data usage, risky areas of code can be found and more test 
cases can be applied.

-Deepak

Hi

Data Flow Testing is a white box tesing, this can done with 
the help of Source code or Design of an application.

S.Ramprasad. sun_ramprasad@yahoo.com

while integrating application how data transfer from one
module to another module is called data flow testing.