The paper also proposed an index structure on the expression signatures based on the conjuncts in their predicates.

The paper also proposed an index structure on the expression signatures based on the conjuncts in their predicates. The concept of expression signatures enables the trigger processing system to exploit the common underlying structure of the triggers and allows for an efficient organization and storage of the trigger classes. Every strategy proposed in the paper towards improving the performance (and hence the scalability) while processing a large number of triggers is based on the expression signatures and the predicate index structure. What are the key concepts behind the approach in this paper?