DBS201: Introduction to Normalization

Agenda Top Down vs Bottom Up What is Normalization? Why Normalization? Normalization Steps

Top Down vs Bottom Up Top Down Usually provided just a narrative or very high level data requirements Need to discover entities, attributes, relationships Result is tables

Top Down vs Bottom Up Bottom Up Provided with views of data Views can be screen shots or reports (printouts) Views contain fields (data) Need to groups fields together – find fields that are in common Result is tables

Agenda Top Down vs Bottom Up What is Normalization? Why Normalization? Normalization Steps

What is normalization? Normalization Process for evaluating and correcting table structures to minimize data redundancies helps eliminate data anomalies Can be used in conjunction with ER modeling to produce a good database design

What is normalization? Works through a series of stages called normal forms: Normal form (1NF) Second normal form (2NF) Third normal form (3NF)

What is normalization? 2NF is better than 1NF 3NF is better than 2NF For most business database design purposes, 3NF is highest we need to go in the normalization process Highest level of normalization is not always most desirable

Agenda Top Down vs Bottom Up What is Normalization? Why Normalization? Normalization Steps

Why normalization? Example: company that manages building projects Charges its clients by billing hours spent on each contract Hourly billing rate is dependent on employee’s position Periodically, a report is generated that contains information displayed as in Table 5.1

A Sample Report Layout

A Table in the Report Format

Why normalization? Structure of data set in Figure 5.1 does not handle data very well The table structure appears to work; report is generated with ease Unfortunately, the report may yield different results, depending on what data anomaly has occurred

Agenda Top Down vs Bottom Up What is Normalization? Why Normalization? Normalization Steps

Conversion to First Normal Form Relational table must not contain repeating groups Repeating group Derives its name from the fact that a group of multiple (related) entries can exist for any single key attribute occurrence Normalizing the table structure will reduce these data redundancies Normalization is three-step procedure

Step 1: Eliminate the Repeating Groups Present data in a tabular format, where each cell has a single value and there are no repeating groups Eliminate repeating groups by eliminating nulls, making sure that each repeating group attribute contains an appropriate data value

First Normal Form

Step 2: Identify the Primary Key Primary key must uniquely identify attribute values (a row) Primary key is PROJ_NUM, EMP_NUM (because the combination of those two uniquely identifies each row of the table)

Step 3: Identify all Dependencies Dependencies can be depicted with the help of a diagram Dependency diagram: Depicts all dependencies found within a given table structure Helpful in getting bird’s-eye view of all relationships among a table’s attributes Use makes it much less likely that an important dependency will be overlooked

Dependency Diagram 1NF PROJ_NUM PROJ_NAME EMP_NUM EMP_NAME JOB_CLASS CHG_HOUR HOURS

First Normal Form Tabular format in which: All key attributes are defined There are no repeating groups in the table All attributes are dependent on primary key All relational tables satisfy 1NF requirements Some tables contain partial dependencies Dependencies based on only part of the primary key Still subject to data redundancies EMPLOYEE_PROJECT(PROJ_NUM(PK), EMP_NUM(PK), PROJ_NAME, EMP_NAME, JOB_CLASS, CHG_HOUR, HOURS)

Conversion to Second Normal Form Relational database design can be improved by converting the database into second normal form (2NF) Two steps

Step 1: Identify All Key Components Determine which attributes are dependent on which other attributes Using the dependency diagram, document the partial dependencies: in other words take each part of the primary key and document which attributes are dependent on each part of the primary key

Dependency Diagram 2NF 1NF PROJ_NUM PROJ_NAME EMP_NUM EMP_NAME JOB_CLASS CHG_HOUR HOURS

Step 2: Identify the Dependent Attributes Write each key component on separate line, and then write the original (composite) key on the last line Each component will become the key in a new table PROJECT (PROJ_NUM (PK), PROJ_NAME) EMPLOYEE (EMP_NUM(PK), EMP_NAME, JOB_CLASS, CHG_HOUR) EMPLOYEE_PROJECT(PROJ_NUM(PK), EMP_NUM(PK), HOURS)

Second Normal Form Table is in second normal form (2NF) if: It is in 1NF and It includes no partial dependencies: No attribute is dependent on only a portion of the primary key

Conversion to Third Normal Form Data anomalies created are easily eliminated by completing these steps

Step 1: Identify Each New Determinant For every transitive dependency, write its determinant as a PK for a new table Determinant Any attribute whose value determines other values within a row Using the dependency diagram, document the transitive dependencies: in other words identify the attributes dependent on each determinant identified above and identify the dependency

Dependency Diagram 3 NF 2NF 1NF PROJ_NUM PROJ_NAME EMP_NUM EMP_NAME JOB_CLASS CHG_HOUR HOURS JOB_CLASS is a determinant because it can determine other values within the row. In this case, it’s the CHG_HOUR

Step 2: Name the table Name the table to reflect its contents and function PROJECT (PROJ_NUM (PK), PROJ_NAME) EMPLOYEE (EMP_NUM(PK), EMP_NAME) JOB (JOB_CLASS(PK), CHG_HOUR) EMPLOYEE_PROJECT(PROJ_NUM(PK), EMP_NUM(PK), HOURS)

Third Normal Form A table is in third normal form (3NF) if: It is in 2NF and It contains no transitive dependencies

Improving the Design Table structures are cleaned up to eliminate the troublesome initial partial and transitive dependencies Normalization cannot, by itself, be relied on to make good designs It is valuable because its use helps eliminate data redundancies

Improving the Design (continued) The following changes should be made: PK assignment Naming conventions Attribute atomicity Adding attributes Adding relationships (will define the FKs) Refining PKs Eliminate derived attributes

Business Rules Business Rules drive the relationships Look at the data in the table and understand/interpret what the relationship is between the data

Business Rules A job class can have more than 1 employee in it; results in a 1:M relationships between JOB and EMPLOYEE Add the FKs into the appropriate tables

Step 2: Name the table Name the table to reflect its contents and function PROJECT (PROJ_NUM (PK), PROJ_NAME) EMPLOYEE (EMP_NUM(PK), EMP_NAME, JOB_CLASS(FK)) JOB (JOB_CLASS(PK), CHG_HOUR) EMPLOYEE_PROJECT(PROJ_NUM(PK), EMP_NUM(PK), HOURS) New foreign key Business rule not necessary between EMPLOYEE and PROJECT. Why?

First Normal Form

Normalization and Database Design Normalization should be part of design process Make sure that proposed entities meet required normal form before table structures are created ER diagram Provides the big picture, or macro view, of an organization’s data requirements and operations Created through an iterative process Identifying relevant entities, their attributes and their relationship Use results to identify additional entities and attributes

ERD

Normalization and Database Design (continued) Normalization procedures Focus on the characteristics of specific entities A micro view of the entities within the ER diagram Difficult to separate normalization process from ER modeling process Two techniques should be used concurrently

Summary Normalization is a table design technique aimed at minimizing data redundancies First three normal forms (1NF, 2NF, and 3NF) are most commonly encountered Normalization is an important part—but only a part—of the design process Continue the iterative ER process until all entities and their attributes are defined and all equivalent tables are in 3NF

Normalization Exercise STU_NUM STU_LNAME STU_MAJOR DEPT_CODE DEPT_NAME DEPT_PHONE 211343 Stephanos Accounting ACCT 4356 200128 Smth 199876 Jones Marketing MKTG 4378 Ortiz 223456 McKulski Statistics MATH Mathematics 3420 Normalize the above table. 1NF – eliminate repeating groups, identify a PK for the table structure 2NF – find partial dependencies 3NF - find transitive dependencies Write final table structures, including all relationships. Make all attributes atomic.

Normalization Exercise Vehicle Num Model Year Acme Tire Number Tire Manfctr Size KM This Vehicle 11 Ford 1997 1327 Goodyear 15R7 43000   1328 1329 25000 1330 24000 15 Chevrolet 1999 2013 BF Goodrich 18000 2014 29000 Normalize the above table. 1NF – eliminate repeating groups, identify a PK for the table structure 2NF – find partial dependencies 3NF - find transitive dependencies Write final table structures, including all relationships. Make all attributes atomic.