Normalization ACSC 425 Database Management Systems

Overview What is normalization? What are the normal forms? How to normalize relations?

Introduction Question: How many, and what, relations (tables) should be used to store my data? Is the current relation free of problems?

Normalization Normalization is a process of producing a set of related relations(tables) with desirable attributes, given the data requirements of a domain The goal is to remove redundancy and other data modification (insertion, update and deletion) problems Usually dividing a table into 2 or more tables Using Normal Forms as a guide

Normal Forms Fewer abnomallies... Normalization …but more tables Normal forms are guidelines (steps) for the normalization process Fewer abnomallies... Normalization …but more tables Unnormalized Form (UNF) 1st Normal Form (1NF) 2nd Normal Form (2NF) 3rd Normal Form (3NF) Boyce Codd Normal Form (BC/NF) 4th Normal Form (4NF) 5th Normal Form DK/NF

Normalization – 1NF A table is in 1NF if it satisfies the definition of a relation Review: what are the characteristics of a relation? No “repeating groups” (columns)

Relation A relation is a two-dimensional table that has specific characteristics: The table consist of rows and columns Rows contain data about entity instances All values in a row describes the same entity instance Columns contain data about attributes of the entity All values in a column are of the same kind 7

Relation (continued) Relation’s specific characteristics go on: Each row is distinct A Cell of the table hold a single value Each column has a unique name The order of the rows is unimportant The order of the columns is unimportant 8

Repeating Groups Customer ID First Name Surname Telephone Number 123 Robert Ingram 555-861-2025 456 Jane Wright 555-403-1659 555-776-4100 789 Maria Fernandez 555-808-9633 Customer ID First Name Surname Tel. No. 1 Tel. No. 2 Tel. No. 3 123 Robert Ingram 555-861-2025 456 Jane Wright 555-403-1659 555-776-4100 789 Maria Fernandez 555-808-9633

Transforming to 1NF Transforming to rows, rather than columns Customer ID First Name Surname Telephone Number 123 Robert Ingram 555-861-2025 456 Jane Wright 555-403-1659 555-776-4100 789 Maria Fernandez 555-808-9633

Transforming to 1NF: Example Another example UNF 1NF

Problems in 1NF Basically has the same problem as the spreadsheet tables Redundancy Data may be inconsistent after modification

Non-Relation Examples Single value Column same kind, row describes the complete instance 13

Non-Relation Examples (2) Emp_Name Emp_Age Emp_Phone Emp_Email Jordan Hail 45 404-652-6325 678-584-1754 JH@work.com, JH@home.com Jack Parsons 28 404-652-8745 404-321-5687 JP@work.com Tom Jackson 23 678-854-1245 770-415-8415 TJ@work.com, TJ@home.com Liz Marsten Thirty 404-884-8753 404-697-2587 RM@work.com, RM@home.com Single value Column same kind, row describes the complete instance 14

Higher Normal Forms Normal forms higher than 1NF deal with functional dependency Identifying the normal form level by analyzing the functional dependency between attributes (fields)

Functional Dependency If each value of attribute A is associated with only one value of attribute B, we say A determines B Or, B is dependent on A Denoted as: A  B Functional dependence describes relationships between attributes (not relations) Note: A (or B) could be a set of fields

Functional Dependency Examples For each SSN, there is only one corresponding first name (or last name), so: SSN determines FirstName SSN  FirstName Non-dependency example Each instructor teaches multiple courses, so: InstructorId does not determines CourseNumber

Functional Dependency and Keys By definition, a primary key (candidate key) functionally determines all other attributes Primary key Surrogate key Composite primary key Dependency diagram ISBN Title PubDate ListPrice

Functional Dependency Exercise CustomerNum  CustomerName? {Street, City, State}  Zip? CustomerName  Balance? State (?) Zip RepNum ( ? ) CustomerName

Normalization – 2NF A relation is in 2NF, if Partial dependency A B C It is in 1st normal formal, and All nonkey attributes must be functionally dependent on the whole primary key (Full dependency) No partial dependency It implies that a relation is in 2NF if there is a single-attribute primary key (candidate key) Partial dependency A non-key attribute is dependent on part of a primary key A B C D

Transforming to 2NF A B C D A B C B D Identify primary key (PK) If PK consists of only one field, then it is in 2NF If PK is a composite key, then analyze functional dependency between part of primary key and other non-key attributes Move partial dependency involved attribute to another relation A B C D A B C B D

A Relation in 1NF but Not in 2NF Partial dependency

Transforming to 2NF: Example Order Order Product OrderItem

Problems in 2NF Again, redundancy and potential inconsistency

Normalization – 3NF A relation is in 3NF, if Transitive dependency It is in 2nd normal formal, and All attributes must, and only, be functionally dependent on candidate keys No transitive dependency Transitive dependency A  B and B  C, then A  C A B C D

A Relation in 2NF but Not in 3NF Identify primary key (PK) and Look for transitive dependence Transitive dependency

Transforming to 3NF Move the attributes involved in transitive dependency to another relation Order Customer

Some Practical Tips If there are attributes of two different entities in one table, there are usually problems To identify the normalization level, determine the primary key first; then look for partial dependence and transitive dependence Generally relations in the 3rd normalization forms are considered to be well formed; going higher may introduce unnecessary structural complexity which is inefficient for data queries Very often tables can go for lower normal forms (de-normalization) depending on design requirements

Normalization Exercise 1-1 Which normal form is the above table in? 1NF 2NF 3NF UNF

Normalization Exercise 1-2 Which normal form is the above table (2nd one) in? 1NF 2NF 3NF UNF

Normalization Exercise 1-3 Which normal form is the above table (first one) in? 1NF 2NF 3NF UNF

Normalization Exercise 1-4 Final database design with 3 tables

Summary

Summary Key concepts Normalization Normal forms Functional dependency