Slide 15 of 21
Notes:
- Joe has the same salary as Fred:
- always replace EMP(salary = E.salary)
- where EMP.name = “Fred” and E.name =
“Joe”
- NEW- ON event (TO) object WHERE POSTQUEL-qualification
- THEN DO [instead] POSTQUEL-command(s)
- instead-POSTQUEL command(s) is to be performed instead of
the action which caused the rule to activate, no instead,
action is done in addition to the user event.
- Forward chaining:Rules specifying additional actions to
be taken as a result of user updates.
- Backward Chaining: If initial data is not stored, i.e.
Fred’s salary is not stored, then additional rules
must be stored to find the ultimate answer.
- Rule Chooser for rewrite vs. record level/trigger
- p.16 No Fred, 1 Fred, N Freds
