At the end of the 80's Ceri and Widom were researching the fundamentals of integrity constraints in databases. In 2000 they were invited by the VLDB conference to review 10 years of work around Constraints and Triggers with an eye on the practical application of both abstractions. The resulting paper gives a good overview of the fundamentals of both concepts.
Practical Applications of Triggers and Constraints: Success Stories and Lingering Issues, Stefano Ceri, Roberta Cochrane, and Jennifer. Widom, In 26th Very Large Data Bases Conference Proceedings, Cairo, September 2000, Pages 254-262