Specification, Semantics, and Enforcement of Dynamic Database Constraints

Abstract

In order to specify dynamic constraints, we ~lrcsfnt * a siclplifjcd vel-sion of teopcltal lccic hasec! on the tenporal quarltjfjcrs “~l\\:eys ” cind “so~c~:.ine ” as well as their bcuncieii ve: s ions “always..unt.i 1 ” and “samet.ire..hefore”.!!C rittor t::at,!n rlcst practical cases, the Ilounded tecpol a1 quar:tifiers can be oxpresscd by nppropri att fotm~!las \\:i th unhcundcc: tenpor; I q”ant ifiets. IJe t’t.cn use special kinds of tt*mpcltal fcdrr-ctlas as a language to specify c’pIiiItYiC constriiints. The problerr. of enfcBrcir.g st1c.h CLIPstrzints is t!ler; reduced to the l~rot!e ~ cf cnfz,rcirg dynoslic,ally changing sets cf two 1,irds of static c.onstt-hints, called universal ant1 existertial constrafnts. Vhilc unicel sal constrziats can t:c cpforced strict];. ir principle, vic;l?t ion of rsi.stent;‘*l constraints cannot he detected in eac! ~ case ft tl:c. cr\\rlif.:;t;:or:ent. Ile give a sufficjcnt criterion fcr detcctin:; vicl;tier 0C e> ist0t icl c.onstraints.