Difference between a Form & a global variable?

Hello

Im trying to obtain all form variables of the completed tasks. If I understood correctly there is no API for this.

I tried to trace down my form variable in the database (see the image below), based on the TaskID.

the question is, how do you get only Form variables?

From the ACT_HI_DETAIL table I did not find a difference between a form & a global variable.