Term
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Definition
Extended Entity Relationship Diagram
Includes entity supertypes and subtypes |
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Term
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Definition
Depicts arrangement of supertypes and subtypes
One to one relationship "Is a"
Subtype exists only within context of supertype
Every subtype has only one supertype to which it is directly related
Can have many levels of supertype subtype relationships |
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Term
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Definition
Enables entity subtype to inherit attributes and relationships of supertype
Subtypes inherit primary key of supertype |
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Term
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Definition
Attribute in supertype entity
Determines to which entity subtype each supertype occurrence is related |
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Term
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Definition
Non-overlapping subtypes
Subtypes that contain unique subset of supertype entity set |
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Term
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Definition
| Subtypes that contain nonunique subsets of supertype entity set |
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Term
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Definition
Specifies whether entity supertype occurrence must be a member of at least one subtype
Partial Completeness
Total Completeness |
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Term
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Definition
| Not every record in the parent entity will appear in at least one sub entity |
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Term
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Definition
| Every record in the superentity must be included in a sub entity |
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Term
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Definition
Top Down Process
Based on grouping unique characteristics and relationships of the subtypes |
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Definition
Bottom up process
Based on grouping common characteristics and relationships of the subtypes |
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Term
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Definition
| A virtual entity that represents multiple entities and relationships in ERD |
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Term
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Definition
| A real world identifier used to uniquely identify |
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Term
| Composite Primary Keys are Useful |
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Definition
As identifiers of composite entities
As identifiers of weak entites |
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Term
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Definition
Auto Number
Used when there is no natural key
Used when selected candidate key is too long or cumbersome |
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Term
| If there is a one to one relationship where do you put the foreign key |
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Definition
If both tables are equal in size it does not matter
If one table is small and the other is large put the foreign key in the smaller table |
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Term
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Definition
Values change over time
Must keep a history of data changes |
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Term
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Definition
| You need to include a bridge |
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Term
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Definition
| When relationship is improperly or incorrectly identified |
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Definition
Most common design trap
When one entity is in two 1:M relationships to other entities |
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Term
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Definition
Occur when there are multiple relationship paths between related entities
Sometimes used to simplify the design |
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Term
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Definition
Occur when there are multiple relationship paths between related entities
Sometimes used to simplify the design |
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Term
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Definition
| Translate specific real-world environment into data model |
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