Give the exact syntactic rules for constructing the triggering graphs from the sets of SQL triggers and foreign-key constraints.

Question

What will be an ideal response?

Answer 1

For each SQL trigger the activating event is an update, deletion, or insertion of/from/into the relation speci?ed in the CREATE TRIGGER ...BEFORE/AFTER ... ON Tab l e clause. Whether the actually event must be an update, deletion or insertion depends on what is speci?ed in the BEFORE/AFTER clause. The events produced by the trigger are updates, insertions, and deletions on the relations speci?ed in the action part of the trigger. (The exact type of the event depends on the form of the action speci?ed.)
Note that a trigger with the FOR EACH STATEMENT clause produces only one event, while a trigger with the FOR EACH ROW clause produces one event per updated/inserted/deleted tuple (whichever applies).
For a foreign-key constraint, the activating event is any update or deletion that involves the relation mentioned in the REFERENCES clause and the events produced are updates or deletions on the relation mentioned in the CREATE TABLE statement,
which this foreign key is part of.
The triggering graph then consists of the edges among all these triggers and foreign-key constraints. An edge is drawn from one trigger/constraint T to another, S, if T produces an event that activates S.