EER to Relational Model Flashcards Preview

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Flashcards in EER to Relational Model Deck (19):
1

Tuple

One row of a relation

2

Attribute

One column of a relation

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Relation

An entire table of related attributes

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Domain of an Attribute

All the possible values an attribute is allowed to have

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Table is a:

Relation

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Column Header is a:

Attribute

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All possible column values are:

Domain

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Row is a:

tuple

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Table Definition:

Schema of a relation

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Populated table:

State of the relation

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SuperKey of R

A subset of the relation attributes where all the tuple values must be distinct

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A key is a:

minimal superkey

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Candidate Keys

Unique keys that could have been chosen to be the primary key

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Primary Key

An arbitrarily chosen candidate key (requires uniqueness)

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ER to Relational Schema:

1. Map regular entities
Separate attributes
2. Map weak entities
Weak entities get foreign key of their parent entity
3. Map M:1 Relationships
the M side gets the foreign key
4. Map 1:1 Relationships
both sides get the foreign key, ore could merge the
table, or could have an intermediate table
5. Map M:N relationships
create a new table with the foreign keys
6. Map multi valued attributes
Create a new table

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Foreign Key

Same domain as the primary key that it maps from, but could have different names

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Referential Integrity

Controlled through semantics. If you delete a primary key that is a foreign key elsewhere, you have to fix that

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Illegal States: Delete

Restricted: Delete is restricted from happening
Cascades: Removes offending entry
Nullifies: FK is set to null

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Illegal States: Update

Restricted: Update is restricted
Cascade: Change the values for all offending entries