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23 Cards in this Set
- Front
- Back
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A functional dependency in which one or more non-key attributes are functionally dependent on part (but not all) of the primary key.
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Partial Functional Dependency
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The process of transforming the conceptual data model into a logical data model.
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Logical DB Design
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Model design that conforms to the data model for a class of database management systems.
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Logical data model
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The deliverable from logical database design
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Normalized relations
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Data duplication
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Redundancy
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Redundancy
Multiple value problems Update anomalies Insertion anomalies Deletion anomalies |
Problems with a "flat" database
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Conceptual Data Model (E-R Diagram)
1) Represent Entities 2) Represent Relationships 3) Normalize the Relation 4) Merge the Relation Logical Data model |
4 Steps in Logical Design Process
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Each entity in an E-R diagram is represented as a relation (a named two-dimensional table of data)
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Represent Entities
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Primary key of a relation is a foreign key of another (or)
Create a separate relation |
Represent Relationships
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Redesign for well structured relations that avoid anomalies
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Normalize the relations
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Delete redundant relations
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Merge the relations
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A named two-dimensional table of data. Consists of a finite set of named columns and an arbitrary number of unnamed rows.
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Relation
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Relation rows correspond with entity instances
Relation columns correspond with attributes |
ER correspondence to Relations
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An attribute (or combination of attributes) that uniquely identifies each row in a relation (guarantees all rows are unique)
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Primary Key
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Attribute that appears as a non-key attribute in one relation and as a primary key attribute (or part of a primary key) in another relation.
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Foreign Key
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The primary key attribute (or a component of primary key attribute) can never be null.
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Entity Integrity
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Either each foreign key value must match a primary key value in the other relation or the foreign key value must be null
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Referential Integrity
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Name of relation is name of Entity
Each simple attribute of entity becomes an attribute or column of relation Identifier of entity becomes primary key of relation |
Regular Entity
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Include all simple attributes
Include the primary key of the owner relation as a foreign key attribute in this new relation The primary key of this new relation is a combination of the primary key of the owner and the partial identifier of the entity |
Mapping a weak entity
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Entity whose existence depends on another entity
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Weak entity
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-Primary key on the mandatory side becomes a foreign key on the optional side
-Primary key on the one side becomes a foreign key on the many side -Create a new relation with primary keys of the two entities as its primary key |
One-to-one
One-to-many Many-to-many |
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Two different names are used for the same attribute
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Synonyms
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One attribute name is used for two or more different attributes
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Homonym
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