Lecture # 17 Chapter # 10 Normalization Database Systems

Bad Database Design Duplication of data Updating Deleting

Redundant

Deleting

Update

Normalization is a design technique that is widely used as a guide in designing relational databases. Normalization is essentially a two step process that puts data into tabular form by removing repeating groups and then removes duplicated data from the relational tables. Normalization theory is based on the concepts of normal forms. A relational table is said to be in a particular normal form if it satisfied a certain set of constraints. There are currently five normal forms that have been defined. In this course, we will cover the first three normal forms Normalization

The goal of normalization is to create a set of relational tables that are free of redundant data and that can be consistently and correctly modified or updated. This means that all tables in a relational database should be in the third normal form (3NF).

Normalization A relational table is in 3NF if and only if all non-key columns are: – Mutually independent and – Fully dependent upon the primary key Mutual independence means that no non-key column is dependent upon any combination of the other columns The first two normal forms are intermediate steps to achieve the goal of having all tables in 3NF In order to better understand the 2NF and higher forms, it is necessary to understand the concepts of functional dependencies

Functional Dependencies The concept of functional dependencies is the basis for the first three normal forms. A column, Y, of the relational table R is said to be functionally dependent upon column X of R if and only if each value of X in R is associated with precisely one value of Y at any given time. X and Y may be composite. Saying that column Y is functionally dependent upon X is the same as saying the values of column X identify the values of column Y. If column X is a primary key, then all columns in the relational table R must be functionally dependent upon X. A short-hand notation for describing a functional dependency is: R.x —> R.y which can be read as in the relational table named R, column x functionally determines (identifies) column y in the relational table R.

Example FD Drinkers(name, addr, drinkLiked, manf, favdrink). Reasonable FD’s to assert: 1.name -> addr 2.name -> favdrink 3.drinkLiked -> manf Functional Dependency: The value of one attribute (the determinant) determines the value of another attribute

Example DF nameaddr drinkLiked manffavDrink JanewayVoyager Bud A.B.WickedAle JanewayVoyager WickedAle Pete’sWickedAle SpockEnterprise Bud A.B.Bud Because name -> addr Because name -> favDrink Because drinkLiked -> manf

Basic Idea To know what FD’s hold in a projection, we start with given FD’s and find all FD’s that follow from given ones. Then, restrict to those FD’s that involve only attributes of the projected schema.

Normalization What is normalization? Basically, it's the process of efficiently organizing data in a database. There are two goals of the normalization process: Eliminate redundant data (for example, storing the same data in more than one table) and Ensure data dependencies make sense (only storing related data in a table). Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored.

First Normalization Form 1FN Eliminate duplicative columns from the same table. BY the values in each column of a table are atomic. By atomic we mean that there are no sets of values within a column. Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).

First Normal Form No multivalued attributes Every attribute value is atomic Fig is not in 1 st Normal Form (multivalued attributes)  it is not a relation Fig is in 1 st Normal form All relations are in 1 st Normal Form

Table with multivalued attributes, not in 1 st normal form Note: this is NOT a relation

Table with no multivalued attributes and unique rows, in 1 st normal form Note: this is relation, but not a well-structured one

Second normal form 2NF Where the First Normal Form deals with atomicity of data, the Second Normal Form (or 2NF) deals with relationships between composite key columns and non- key columns: – Meet all the requirements of the first normal form. – Any non-key columns must depend on the entire primary key. In the case of a composite primary key, this means that a non-key column cannot depend on only part of the composite key. – Create relationships between these new tables and their predecessors through the use of foreign keys. – A relation R is in 2nf if every non-primary attribute A in R is fully Functionally dependent on the primary key.

Second Normal Form 1NF PLUS every non-key attribute is fully functionally dependent on the ENTIRE primary key – Every non-key attribute must be defined by the entire key, not by only part of the key – No partial functional dependencies

Order_ID  Order_Date, Customer_ID, Customer_Name, Customer_Address Therefore, NOT in 2 nd Normal Form Customer_ID  Customer_Name, Customer_Address Product_ID  Product_Description, Product_Finish, Unit_Price Order_ID, Product_ID  Order_Quantity

Getting it into Second Normal Form Partial Dependencies are removed, but there are still transitive dependencies

Third normal form 3NF Remove columns that are not dependent upon the primary key. Third Normal Form (3NF) requires that all columns depend directly on the primary key. – Example: Publisher (Publisher_ID, Name, Address, City, State, Zip) Zip (Zip, City, State)

Third Normal Form 2NF PLUS no transitive dependencies (functional dependencies on non-primary-key attributes) Note: this is called transitive, because the primary key is a determinant for another attribute, which in turn is a determinant for a third Solution: non-key determinant with transitive dependencies go into a new table; non-key determinant becomes primary key in the new table and stays as foreign key in the old table

Getting it into Third Normal Form Transitive dependencies are removed

Figure Steps in normalization