Distributed Database Management Systems: Lecture 6

Distributed Database Management Systems: Lecture 6. The main topics covered in this chapter include: first three normal forms; boyce-code normal form; fourth normal form; P-J dependency; project-join dependency; integrity rules;...

Distributed Database Management System Lecture 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 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 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 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 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