Mutsumi Nakamura Chitta Baral Invariance, Maintenance, and Other Declarative Objectives of Triggers - A Formal Characterization of Active Databases. 1210-1224 http://link.springer.de/link/service/series/0558/bibs/1861/18611210.htm 2000 conf/cl/2000 Computational Logic db/conf/cl/cl2000.html#NakamuraB00