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Understanding Functional Dependencies and Normal Forms in Database Design

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This lecture discusses the fundamentals of functional dependencies and various normal forms, focusing on their importance in relational schema design. Topics include informal design guidelines, definitions of second, third normal forms, and Boyce-Codd normal form, along with multivalued dependencies and join dependencies for fourth and fifth normal forms. The discussion covers approaches to database design, quality measures, importance of attribute semantics, and strategies to minimize redundancy and spurious tuples in database schemas, thereby promoting effective database management and integrity.

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Understanding Functional Dependencies and Normal Forms in Database Design

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  1. Chapter 15 Basics of Functional Dependencies • Lecture # 13 July 19 ,2012

  2. Mid Term Exam Solution Discussion

  3. Chapter 15 Outline • Informal Design Guidelines for Relation Schemas • Functional Dependencies • Normal Forms Based on Primary Keys • General Definitions of Second and Third Normal Forms • Boyce-Codd Normal Form

  4. Chapter 15 Outline (cont’d.) • Multivalued Dependency and Fourth Normal Form • Join Dependencies and Fifth Normal Form

  5. Introduction • Levels at which we can discuss goodness of relation schemas • Logical (or conceptual) level • Implementation (or physical storage) level • Approaches to database design: • Bottom-up or top-down

  6. Informal Design Guidelinesfor Relation Schemas • Measures of quality • Making sure attribute semantics are clear • Reducing redundant information in tuples • Reducing NULL values in tuples • Disallowing possibility of generating spurious tuples

  7. Imparting Clear Semantics to Attributes in Relations • Semantics of a relation • Meaning resulting from interpretation of attribute values in a tuple • Easier to explain semantics of relation • Indicates better schema design

  8. Continues…

  9. Guideline 1 • Design relation schema so that it is easy to explain its meaning • Do not combine attributes from multiple entity types and relationship types into a single relation • Example of violating Guideline 1: Figure 15.3

  10. Guideline 1 (cont’d.)

  11. Redundant Information in Tuples and Update Anomalies • Grouping attributes into relation schemas • Significant effect on storage space • Storing natural joins of base relations leads to update anomalies • Types of update anomalies: • Insertion • Deletion • Modification

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