In Barr v. Resolution Trust Corp., 837 S.W.2d 627 (Tex. 1992), the supreme court "reaffirmed" the transactional approach to res judicata, which relates to what claims could have been litigated in a prior lawsuit. See 837 S.W.2d at 631. Under the transactional approach, res judicata may apply if the subsequent suit arises out of the same subject matter as a previous suit and, through the exercise of diligence, could have been litigated in the previous suit. See id. A determination of what constitutes the subject matter of a suit requires an examination of the factual basis of the claims without regard to the form of action. See id. at 630.