The Relational Model and Normalization (2) IS 240 – Database Management Lecture # Prof. M. E. Kabay, PhD, CISSP Norwich University

2 Copyright © 2004 M. E. Kabay. All rights reserved. Topics Review of Modification Anomalies Essence of Normalization Classes of Relations 1 st – 5 th Normal Forms 2 nd Normal Form 3 rd Normal Form Boyce-Codd Normal Form (BCNF) 4 th Normal Form Homework

3 Copyright © 2004 M. E. Kabay. All rights reserved. Review of Modification Anomalies MemberBook 1:N Member_ID Member_Name Member_Address Member_Etc Book_ID Book_Name Book_ISBN Date_Borrowed Member_ID Date_Returned Book_Location What is the Member_ID if the book isnt out? How can we delete a member if there are still records showing the books (s)he borrowed and returned?

4 Copyright © 2004 M. E. Kabay. All rights reserved. Essence of Normalization We run into problems when an entity tries to include attributes that belong to different relations. * Problems occur when a relation contains facts about two different themes. E.g., Storing information describing a book along with information about when it was borrowed Grouping attributes about a member along with information about what (s)he borrowed * Kroenke p. 127

5 Copyright © 2004 M. E. Kabay. All rights reserved. Normalization (contd) When we try to group information about disparate entities into a single relation, we generate modification anomalies Solution is to break up a relation into separate relations that dont mix themes E.g., store information about the member, information about the book, and information about each borrowing in separate relations

6 Copyright © 2004 M. E. Kabay. All rights reserved. Classes of Relations 1970s: Theorists analyzed anomalies Developed names for different types of problems Named relations as normal forms 1NF = first normal form 2NF = second normal form 3NF = third normal form BCNF = Boyce-Codd normal form 4NF = fourth normal form 5NF = fifth normal form (not used)

7 Copyright © 2004 M. E. Kabay. All rights reserved. 1NF – First Normal Form All the relations that we have defined are 1NF: Each cell contains a single value (no lists, tables, arrays) All instances of an attribute (field, column) must be instances of the same quality Every attribute (field, column) is uniquely identified (same name in all tuples (records, rows) Every tuple (record, row) is unique Order of attributes and tuples is arbitrary – many designs are functionally equivalent A group of one or more attributes (fields, columns) that uniquely identifies a tuple (records, row) is called a key Every relation has at least one key No record (tuple, row) may duplicate another

8 Copyright © 2004 M. E. Kabay. All rights reserved. 1 st – 5 th Normal Forms All relations as we have defined them are always in first normal form (1NF) Other normal forms are subsets of 1NF When we split a relation that is in 1NF we generate some other NF

9 Copyright © 2004 M. E. Kabay. All rights reserved. Classes of Relations (contd) 1NF 2NFAnomalies 3NFAnomalies BCNFAnomalies 4NFAnomalies 5NFAnomalies DK/NFAnomalies Thats all, folks! Boyce-Codd Domain/Key

10 Copyright © 2004 M. E. Kabay. All rights reserved. 1st Normal Form Anomalies LIBRARY Book_ID Book_Name Member_ID Member_Name Date_Borrowed Date_Returned Book_Location Book_ID (Book_Name, Book_Location) Member_ID Member_Name (Book_ID, Member_ID) Date_Borrowed, Date_Returned ANOMALIES: Member has no books out? No one has borrowed a book?

11 Copyright © 2004 M. E. Kabay. All rights reserved. 2NF BOOK Book_ID Book_Name Book_Location MEMBER Member_ID Member_Name BORROWING Book_ID Member_ID Date_Borrowed Date_Returned A relation is in 2NF if all its nonkey attributes are dependent on the entire key. Keys in RED

12 Copyright © 2004 M. E. Kabay. All rights reserved. 2 nd Normal Form (contd) MAJOR_INFO Student_ID Major_Name Director_ID ANOMALIES: How will we know who is running a major before a student registers for that major? How do we keep information about whos running a major if the last student registered withdraws from that major? How many records will we have to update if we change the director of a major? Major_Name Director_ID Student_ID Major_Name Director_ID Transitive dependency Only one major per student Only one director per major

13 Copyright © 2004 M. E. Kabay. All rights reserved. 3NF A relation is in 3NF if it is in 2NF and has no transitive dependencies. STUDENT_MAJOR Student_ID Major_Name MAJOR_DIRECTOR Major_Name Director_ID

14 Copyright © 2004 M. E. Kabay. All rights reserved. 3NF Anomalies ElkinsCardiac110 DouglasICU90 CharliePulmonary70 BakerICU55 AbleCardiac50 NurseWardPatient PATIENT AbleCardiac110 Key: (Patient, Nurse) FD*: Nurse Ward Nurse is a determinant yet it is not a possible (candidate) key Anomaly: removing patient 110 will remove fact that Elkins works in the Cardiac ward 3NF *FD = Functional Dependency

15 Copyright © 2004 M. E. Kabay. All rights reserved. Boyce-Codd Normal Form (BCNF) A relation is in BCNF if every determinant is a candidate key. PatientNurse 50Able 55Baker 70Charlie 90Douglas 110Elkins 110Able WardNurse CardiacAble ICUBaker PulmonaryCharlie ICUDouglas CardiacElkins Patient Nurse Ward

16 Copyright © 2004 M. E. Kabay. All rights reserved. Multi-Value Dependencies Suppose a patient can have several diseases Patient Disease The patient can also have several insurers Patient Insurer Storing complete information about patients would require all combinations of patient, disease and insurer; e.g., Patient_IDDiseaseInsurer ALiverPrudential ALiverLiberty AHeartPrudential AHeartLiberty

17 Copyright © 2004 M. E. Kabay. All rights reserved. 4 th Normal Form A relation is in 4NF if it is in BCNF and has no multi-value dependencies. PatientDisease PatientInsurer

18 Copyright © 2004 M. E. Kabay. All rights reserved. Homework Review Chapter 5 material thoroughly REQUIRED: by Tuesday 24 Feb 2004 For 7 points, complete Group 1 questions 5.11 through 5.17 Study to the end of Chapter 5 and then review the entire chapter carefully By next Tuesday the 24th, Work on Ferrett et al. to complete up to and including Project #6 in time for your mid- term exam OPTIONAL: by THURSDAY THE 26 TH FEB, complete Ch 5 FiredUp Project questions A through H for an extra 8 extra points.

19 Copyright © 2004 M. E. Kabay. All rights reserved. DISCUSSION (Reminder: Mid-term Exam Thu 26 th )