Relational Database Appendix

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ER Diagram

Entity/relation

Relationship

Composite Entity

Entity Subtype

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Shorthand Description• State (StateAbbrev, StateName, EnteredUnionOrder, StateBird,

StatePopulation)• Capital (CapitalName, StateAbbrev, YearDesignated, PhoneAreaCode,

CapitalPopulation)– Foreign Key: StateAbbrev to State relation

• City (StateAbbrev, CityName, CityPopulation)– Foreign Key: StateAbbrev to State relation

• Crop (CropName, Exports, Imports)• Production (StateAbbrev, CropName, Quantity)

– Foreign Key: StateAbbrev to State relation– Foreign Key: CropName to Crop relation

• Shipping (StateAbbrev, OceanShoreline, ExportTonnage, ImportTonnage)– Foreign Key: StateAbbrev to State relation

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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

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Dependencies and Determinants

•StateAbbrev functionally determines StatePopulation•StatePopulation is functionally determined by StateAbbrev

•StateAbbrev is a determinant

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Determinants

• 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

Partial Dependencies

Transitive Dependency

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Problematic Dependencies

• Partial Dependency– Funtional dependency on part of the primary

key

• Transitive Dependency– Functional dependency between two nonkey

attributes

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Anomalies

• Insertion 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

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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

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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

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1NF result

• Still problems– Insertion, deletion, and update anomalies in both relations– Caused by partial dependencies (next slide)

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Second Normal Form (2NF)

• A relation in 1NF is in 2NF if it does not contain any partial dependencies

• Process1. Identify functional depencies for each attribute

2. 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

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Result of converting to 2NF

• Still problems?– Transitive

dependency between VetID and VetName

– All 3 anomalies exist in Client relation

• 3NF removes transitive dependencies

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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

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Result of converting to 3NF

• No data redundancy• No anomalies

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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