It is shown how parsing can be described as a problem in the class ISBES, Intersections of Sets and Bags of Extended Substructures, defined in /pubs/1991/161/, by viewing parsing as a generalization of pattern matching in several ways. The resulting description is shown to be a good starting point for the transformational derivation of the Cocke-Kasami-Younger tabular parsing algorithm that follows. This derivation is carried out at the level of bag comprehensions.