In linguistic semantics, a case role is any of the spatially-distinguished parts of a process.

In the sentence, "You do that?", the subject "you" has the case role of "agent" and the object "that" has the case role of "patient".

The meaningful case roles are dependent on the process. eg:

for process crime, case roles could be: perpetrator + victim + evidence + modus operandi;

for process burn, case roles could be: fuel, air, heat

The term has its origins in linguistic semantics, but is used in computerized natural language processing, where a reasoning engine performs case role analysis to establish progressively more specialized case roles from speech: 'subject', 'agent', 'mother', 'Fred's mother', being the progression that results from the 'you gave birth to Fred.'.

References:

IEEE SUMO

http://www.ipsj.or.jp/members/SIGNotes/Eng/01/1995/107/article012.html

http://www.uoregon.edu/~delancey/papers/bls91.html