1. Review of Week 3 Relation Transforming ERD into Relations
Map entity
Map relationship: 1-1, 1-M, M-N
Functional dependency
Primary key definition
Partial
Transitive
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2. Module 2 Database Design Concepts

3. Chapter 5 Normalization of Database Tables
Module 2: Database Design Concepts

4. Normalization
Process for evaluating and improving table structures to minimize data redundancies
Process of decomposing relations with anomalies to produce smaller, well-structured relations
1NF
2NF
3NF
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5. Well Structured Relations
A well structured relation contains minimal redundancy and allows users to insert, modify and delete the rows in a table without errors or inconsistencies.
General rule of thumb: a relation should not pertain to more than one entity
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6. Data Anomalies
Redundancies or anomalies are errors or inconsistencies that may result when a user attempts to update a table that contains redundant data. There are three types:
Insertion anomaly: adding new rows forces user to create duplicate data
Deletion anomaly: deleting rows may cause a loss of data that would be needed for other future rows
Update anomaly: changing data in a row forces changes to other rows because of duplication
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7. A Table in the Report Format
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8. Examples of Data Anomalies
Insertion anomaly: a new project or a new employee
Deletion anomaly: remove a project or an employee
Update anomaly: modify Job_class for employee 105 (many alterations), or 103 (lost information on Elec. Engineer)
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9. Conversion to 1NF
Relational database design is required to be in first normal form (1NF)
Three steps
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10. 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
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11. Data Organization: Step 1
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12. Step 2: Identify Primary Key
Primary key must uniquely identify attribute value
New key must be composed
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13. Step 3: Identify all Dependencies
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
Makes it much less likely that an important dependency will be overlooked
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14. A Dependency Diagram: First Normal Form (1NF)
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15. 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
Sometimes used for performance reasons, but should be used with caution
Still subject to data redundancies
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16. Conversion to 2NF
Relational database design can be improved by converting the database into second normal form (2NF)
Two steps
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17. Step 1: Identify All Key Components
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
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18. Step 2: Identify the Dependent Attributes
Determine which attributes are dependent on which other attributes
At this point, most anomalies have been eliminated
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19. Second Normal Form (2NF) Conversion Results
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20. 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
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21. Conversion to 3NF
Data anomalies created are easily eliminated by completing three steps
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22. 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
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23. Step 2: Identify the Dependent Attributes
Identify the attributes dependent on each determinant identified in Step 1 and identify the dependency
Name the table to reflect its contents and function
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24. Step 3: Remove Transitive Dependencies
Eliminate all dependent attributes in transitive dependencies from each table that has such a transitive relationship
Draw a new dependency diagram to show all tables defined in Steps 1–3
Check new tables and modified tables from Step 3 to make sure that each has a determinant and does not contain inappropriate dependencies
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25. Third Normal Form (3NF) Conversion Results
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26. Third Normal Form A table is in third normal form (3NF) if:
It is in 2NF and
It contains no transitive dependencies
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27. 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
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28. The Completed Database
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29. The Completed Database (cont’d)
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30. Activity
Table P5.11 on Page 216
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31. Normalization and Data Design
Normalization should be part of design process
Make sure that proposed entities meet required normal form before table structures are created
Many real-world databases have been improperly designed or burdened with anomalies if improperly modified during course of time
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32. Normalization and Data Design (continued)
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
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33. Normalization and Data 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
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34. The Initial ERD
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35. The Modified ERD
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36. The Final ERD
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37. Higher-Level Normal Forms
BCNF
4NF
5NF
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38. Denormalization
Creation of normalized relations is important database design goal
Processing requirements should also be a goal
If tables decomposed to conform to normalization requirements
Number of database tables expands
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39. Denormalization (continued)
Joining larger number of tables takes additional disk input/output (I/O) operations and processing logic
Reduces system speed
Conflicts among design efficiency, information requirements, and processing speed are often resolved through compromises that may include denormalization
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40. Denormalization (continued)
Use denormalization cautiously
Understand why—under some circumstances—unnormalized tables are a better choice
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41. Wrap Up Review course website Assignment 4-1 Assignment 4-2
Assignment 4-1
Use the table P5.15 on page 217 as the initial relation, and normalize it to 3NF
Assignment 4-2
In assignment4-2.doc
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