Distributed Database Management System Lecture 6

First Three Normal Forms First Normal Form Second Normal Form: we are not much interested in it. Its more of a historical perspective Third Normal Form: 3NF, for each XY where Y is not in X, either X is a superkey of R or Y is prime attribute Virtual University of Pakistan

Boyce-Code Normal Form BCNF, For every FD X  Y in R, X is the superkey Removal of second part creates situation where a relation in in 3NF but not in BCNF, vice versa never happens Virtual University of Pakistan

Virtual University of Pakistan A relation R defined on attributes A(A1, A2, …., An), if XA, YA, ZA, if for each value of X, there is a unique value of (Y,Z) pair and Z depends only on X then X multidetermines Z, X > Z and also X > Y Virtual University of Pakistan

Virtual University of Pakistan Fourth Normal Form If a relation is in BCNF and all MVDs are also FDs EMP-PROJ is broken in EMP(eNo, pNo) SKILL(eNo, eSkill) Virtual University of Pakistan

Virtual University of Pakistan P-J Dependency A relation R defined on attributes A(A1, A2, …., An), if XA, YA, ZA, if R is equal to join of X, Y and Z then (X, Y, Z) constitute project-join dependency for R A relation R is in 5NF if every join dependency is implied by the CKs of R Virtual University of Pakistan

Virtual University of Pakistan Integrity Rules Rules to maintain the consistency of DB Structural, Behavioral Beh: help to capture semantics of App Should be verified at each update, since updates can lead to inconsistencies Virtual University of Pakistan