Question: D. Z. Badal and G. J. Popek. "Cost and Performance Analysis of Semantic Integrity Validation Methods." Proc. 1979 ACM International Conference on Management of Data, Boston, Mass. (May/June 1979). Compares three different approaches to the implementation of integrity rules: checking at compilation time (that is, checking by examining database values and the effect of executing the transaction at the time it is compiled); run-time checking (that is, checking at COMMIT but before any writes have been made to the physical database); and post-execution checking (that is, checking after the physical writes have been done). Run-time validation is shown to give the best performance (based primarily on the number of I/O operations needed, but also taking into account such matters as lock duration).