it's all about the Performance Testing
Correlation is used when a recorded script includes a dynamic value (such as a session ID) and therefore cannot be successfully replayed. To resolve this, you convert the dynamic value into a variable—thereby enabling your script to replay successfully.
For example, many applications and Web sites use the current date and time to identify a session. If you try to replay a script that was recorded on such a site, the script may fail because the current time is different from the recorded time. Correlating the data enables you to save the dynamic data and use it throughout the scenario run.
When a correlation is created, VuGen adds a function that extracts the dynamic value to a parameter. Appropriate occurrences of the original value are replaced with a parameter.
With the Correlation tab you can:
The following flow chart illustrates the process for correlating values in your script using the Correlation tab: