Chapter 03 Flashcards

primary key
Terms Definitions
Key
One or more attributes that determine other attributes
Composite Key
Key consisting of two or more attributes
Principle of determination
If you know the value of attribute A you can determine the value of attribute B
Functional Dependence
Attribute B is functionally dependent on A
Attribute A
The dependentONLY ONE
Attribute B
Depends on AMULTIPLE
Superkey
Any column or combination of columns that uniquely identifies
Candidate Key
The most effective superkey that you can obtain.Least amount of columnsStrive for one
Primary Key
The candidate key that you decide to be the primary key
Secondary Key
Helps you obtain certain data a little bit easierFor your convenienceUsually results in multiple records in the outputThen you pick through the output
Foreign Key
Help you link tablesA common field between two tablesMust contain values in the primary key column of the other table
Null Values
Very dangerousEffect calculations and make inadequate results
Integrity Rules
Define requirements for the primary and foreign key columns
Entity Integrity Rules
Primary key columnMust contain unique valuesCan't contain null values
Referential Integrity Rules
Foreign Key columnMust contain values that appear in the primary key column of the related tableMay contain duplicate or null values
Controlled Redundancy
Enables tables to be linked togetherForeign key column
Relational Algebra
Relational operatorsTheoretical way of manipulating table contents
Types of relational algebra operators
SelectProjectJoinIntersectUnionDifferenceProductDivide
Union
Combines all rows from two tables excluding duplicate rows
Intersect
Only shows the rows that appear in both tables
Difference
Only shows rows in table 1 that are not found in table 2
Product
Shows all possible combinations of rows from two tables
Select
Selects data based on a query
Project
Shows all values for selected attributesOnly used when you create joints
Joints
How you retrieve data from two or more tables
Natural Joint
Links tables by selecting rows with common values in common attributes
Outer Joint
List rows from one or more tables even when there are no matching values in the other table. Missing values in the second table are set to null
Composite Entity
Bridge EntityBreaks up M:N relationship
Data dictionary
Holds metadataContains all the attributes names and characteristics for each table in the system
System Catalog
Contains metadataDetailed data dictionary that includes all objects within the database
Index
Speeds up the retrieval processLooks like a tableEach record is listed and given a location
Index Key
Index's reference point
Unique index
Index where index key can only have one row associated with it
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