Lecture Nine: Normalization Introduction to Normalization: redundancy, anormalies? 1st – 3rd Normal Forms 4/25/2017

Objectives Purpose of normalization. Problems associated with redundant data. Identification of various types of update anomalies such as insertion, deletion, and modification anomalies. How to recognize appropriateness or quality of the design of relations. How functional dependencies can be used to group attributes into relations that are in a known normal form. How to undertake process of normalization. How to identify most commonly used normal forms, namely 1NF, 2NF, and 3NF 4/25/2017

Normalization Normalization is defined as a technique for producing a set of well designed relations that measure up to a set of requirements which are outlined in various levels of normalization (or Normal Forms). Most commonly used normal forms are first (1NF), second (2NF) and third (3NF) normal forms. Normalization has the underlying aim of minimizing information redundancy, avoiding data inconsistency and preventing Update anomalies (insertion, deletion, and modification anomalies). 4/25/2017

Data Redundancy Major aim of relational database design is to group attributes into relations to minimize data redundancy and reduce file storage space required by base relations. Problems associated with data redundancy are illustrated by comparing the following Staff and Branch relations with the StaffBranch relation. 4/25/2017

Data Redundancy 4/25/2017

Update Anomalies Relations that contain redundant information may potentially suffer from update anomalies. Types of update anomalies include: Insertion Deletion Modification. Insertion Anomaly: Occurs when extra data beyond the desired data must be added to the database. 4/25/2017

Update anomalies: Insertion Anomaly Until the new faculty member, Dr. Newsome, is assigned to teach at least one course, his details cannot be recorded. 4/25/2017

Update anomalies: Modification Anomaly Modification Anomaly: Changing the value of one of the columns in a table will mean changing all the values that have to do with that column. Employee 519 is shown as having different addresses on different records. 4/25/2017

Update anomalies: Deletion Anomaly Deletion Anomaly: Occurs whenever deleting a row inadvertently causes other data to be deleted. All information about Dr. Giddens is lost when he temporarily ceases to be assigned to any courses. 4/25/2017

Functional Dependency Functional Dependency: Describes relationship between attributes in a relation. If A and B are attributes of relation R, B is functionally dependent on A (denoted A  B), if each value of A in R is associated with exactly one value of B in R. Diagrammatic representation: Main concept associated with normalization. Determinant of a functional dependency refers to attribute or group of attributes on left-hand side of the arrow. 4/25/2017

Functional Dependencies Example branchNo bAddress Functional Dependencies 4/25/2017

Example - Functional Dependency 4/25/2017

Functional Dependencies Example Functional Dependencies 4/25/2017

Example Given TEXT we know the COURSE. TEXT ->COURSE TEXT maps to a single value of COURSE 4/25/2017

The Process of Normalization Formal technique for analyzing a relation based on its primary key and functional dependencies between its attributes. Often executed as a series of steps. Each step corresponds to a specific normal form, which has known properties. As normalization proceeds, relations become progressively more restricted (stronger) in format and also less vulnerable to update anomalies. 4/25/2017

Unnormalized Form (UNF) A table that contains one or more repeating groups. Note: A repeating group is an attribute or group of attributes within a table that occurs with multiple values for a single occurrence of the nominated key attributes for that table. For example a book with multiple authors, etc To create an unnormalized table: transform data from information source (e.g. form) into table format with columns and rows. 4/25/2017

First normal form (1NF) A table is in First Normal Form (1NF) iff all its attributes are atomic. A domain is atomic if its elements are considered to be indivisible units. A relation in which intersection of each row and column contains one and only one value. Implies that it should have no composite attributes or multi-valued attributes. In case a table is not in 1NF, we do two things 4/25/2017

UNF to 1NF First identify a primary key, then Either Place each value of a repeating group on a tuple with duplicate values of the non-repeating data (called “flattening” the table) Or Make a new table to cater for multi-valued attributes. Place repeating data along with copy of the original key attribute(s) into a separate relation The new primary key should be a combination of the (multi-valued) attribute and the primary key of the parent table. 4/25/2017

UNF to 1NF Normalization

UNF to 1NF 4/25/2017

UNF to 1NF 4/25/2017

HEALTH HISTORY REPORT PET ID PET NAME PET TYPE PET AGE OWNER VISIT DATE PROCEDURE PID PNAME 246 ROVER DOG 12 SAM COOK JAN 13/2002 01 RABIES VACCINATION MAR 27/2002 10 EXAMINE and TREAT WOUND APR 02/2002 05 HEART WORM TEST 298 SPOT 2 TERRY KIM JAN 21/2002 08 TETANUS VACCINATION MAR 10/2002 341 MORRIS CAT 4 JAN 23/2001 519 TWEEDY BIRD APR 30/2002 20 ANNUAL CHECK UP EYE WASH 4/25/2017

Second Normal Form (2NF) Based on concept of full functional dependency: A and B are attributes of a relation, B is fully dependent on A if B is functionally dependent on A but not on any proper subset of A. 2NF - A relation that is in 1NF and every non-primary-key attribute is fully functionally dependent on the primary key. It applies to relations that have composite keys for a primary key. Normalization 4/25/2017

1NF to 2NF This involves the removal of partial dependencies A partial dependency occurs when the primary key is made up of more than one attribute (i.e. it is a composite primary key) and there exists an attribute (which is a non-primary key attribute) that is dependant on only part of the primary key. These partial dependencies can be removed by removing all of the partially dependent attributes into another relation along with a copy of the determinant attribute (which is part of the primary key in the original relation) Normalization 4/25/2017

1NF to 2NF 4/25/2017

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Third Normal Form (3NF) Based on concept of transitive dependency: A, B and C are attributes of a relation such that if A  B and B  C, then C is transitively dependent on A through B. (Provided that A is not functionally dependent on B or C). 3NF - A relation that is in 1NF and 2NF and in which no non-primary-key attribute is transitively dependent on the primary key. Normalization 4/25/2017

2NF to 3NF Identify the primary key in the 2NF relation. Identify functional dependencies in the relation. If transitive dependencies exist on the primary key remove them by placing them in a new relation along with copy of their determinant. Normalization 4/25/2017

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Exercises: Instructions The following tables are susceptible to update anomalies. Provide examples of insertion, deletion, and modification anomalies. Describe and illustrate the process of normalizing the tables to 3NF. State any assumptions you make about the data shown in these tables. 4/25/2017

Exercise 1 4/25/2017

Exercise 2 4/25/2017

Exercise 3 4/25/2017