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Relational Database Appendix

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Presentation on theme: "Relational Database Appendix"— Presentation transcript:

1 Relational Database Appendix

2 ER Diagram Entity/relation Entity Subtype Relationship
Composite Entity Bus 311: Fall 2003

3 Shorthand Description
State (StateAbbrev, StateName, EnteredUnionOrder, StateBird, StatePopulation) Capital (CapitalName, StateAbbrev, YearDesignated, PhoneAreaCode, CapitalPopulation) Foreign Key: StateAbbrev to State relation City (StateAbbrev, CityName, CityPopulation) Crop (CropName, Exports, Imports) Production (StateAbbrev, CropName, Quantity) Foreign Key: CropName to Crop relation Shipping (StateAbbrev, OceanShoreline, ExportTonnage, ImportTonnage) Bus 311: Fall 2003

4 Integrity Constraints
Ideally DBMS enforces integrity MS Access does a pretty good job Primary key constraints Must be unique and non-null Referential integrity Each no-null foreign key must match a primary key No ‘orphaned’ foreign keys Domain integrity constraint Rules specified for individual attributes Data type, number of characters etc. Validation rules Bus 311: Fall 2003

5 Dependencies and Determinants
StateAbbrev functionally determines StatePopulation StatePopulation is functionally determined by StateAbbrev StateAbbrev is a determinant Bus 311: Fall 2003

6 Determinants Transitive Dependency Partial Dependencies StateAbbrev is a determinant for StatePopulation, StateBird, and BirdScientificName CropName is a determinant for Exports Quantity is functionally dependent on both StateAbbrev and CropName StateBird is a determinant for BirdScientificName Bus 311: Fall 2003

7 Problematic Dependencies
Partial Dependency Funtional dependency on part of the primary key Transitive Dependency Functional dependency between two nonkey attributes Bus 311: Fall 2003

8 Anomalies Insertion Anomaly Deletion Anomaly Update Anomaly
Can’t add row if don’t know part of primary key Can’t add new client without knowing a ChildName Deletion Anomaly Delete data and unintentionally lose other critical data Delete Client 8112, and lose all info on VetID 24 Update Anomaly Change one attribute and changes must be made other places Change ClientName for ClientID 4519, must change other record too Bus 311: Fall 2003

9 Normalization Process of bringing a relational database to an orderly form Eliminate problems Major process in database design Many normal forms – we consider three First Normal Form (1NF) Second Normal Form (2NF) Third Normal Form (3NF) – aka Boyce-Codd Normal Form (BCNF Bus 311: Fall 2003

10 First Normal Form (1NF) A relation is 1NF if it does not contain repeating groups Process Expand primary key to include primary key of repeating group – Independently for each repeating group Create new relation (table) for each repeating group Bus 311: Fall 2003

11 1NF result Still problems
Insertion, deletion, and update anomalies in both relations Caused by partial dependencies (next slide) Bus 311: Fall 2003

12 Bus 311: Fall 2003

13 Second Normal Form (2NF)
A relation in 1NF is in 2NF if it does not contain any partial dependencies Process Identify functional depencies for each attribute If necessary, create new relations to make each attribute functionally dependent on the entire primary key. New relations should have primary keys that are subsets of the original composite key A relation in 1NF with a single-attribute primary key is automatically in 2NF Bus 311: Fall 2003

14 Result of converting to 2NF
Still problems? Transitive dependency between VetID and VetName All 3 anomalies exist in Client relation 3NF removes transitive dependencies Bus 311: Fall 2003

15 Third Normal Form (3NF) Boyce-Codd Normal Form (BCNF) is an improvement over original 3NF A 2NF relation is in 3NF when there are no transitive dependencies Process Remove attributes that depend on the non-candidate-key (non-primary key) Place in new relation with determinant as primary key Bus 311: Fall 2003

16 Result of converting to 3NF
No data redundancy No anomalies Bus 311: Fall 2003

17 Exercises Gain a better understanding
Do Review Questions at end of RD appendix RQ 1-6 will be on the exam! RQ 7 will help you get a better understanding of how to apply to real-world situations Some of RQ 8-14 are likely to be on the exam If you do RQ 15-18, I will be happy to discuss your solution with you Bus 311: Fall 2003

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