問題一覧
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a class of person place object events or concept about which we need to capture and store data
entity
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five categories of entities
person place objects events concept
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a single occurrence of an entity
entity instance
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a descriptive property or characteristic of an entity
attributes
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an attribute that contains of other attributes
compound attributes
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one of a number of keys that may serve as primary key
candidate key
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a candidate key used to uniquely identify a single entity instance
primary key
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candidate key not selected to become the primary
alternate key
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an attribute whose finite values divide all entity instance into useful subset
subsetting criteria
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a natural business association that exist between one or more entities
relationship
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relationship that exist between instances of the same entity
recursive relationship
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the minimum and maximum number of occurrence of one entity that may be related to single occurrence of the other entity
cardinality
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another measure of the complexity of a data relationship
degree
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entity that inherits its primary key from more one other entity
associative entity
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it connects three entities and it resolves a specific relationship by providing structure and ambiguous data association
ternary relationship
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relationship in which the parent entity key is also part of the primary key of the child entity
identifying relationship
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is a relationship where each participating entity has its own independent primary
non identifying relationship
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a primary key of an entity that is used in another entity or identifying instance of a relationship
foreign key
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is an entity whose instance store attributes that are common to one or more entity subtypes
supertype
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an entity whose instance may inherit common attributes from its entity super type and then and other attributes unique to the subtype
subtype entity
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analyzes used to improve a data model for implementation as a database
data analysis
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three characteristic of a good data model
a good data model is simple a good data model is essentially non-redundant a good data model should be flexible and adaptable to future needs
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three steps of normalization
first normal form second normal form third normal form
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a calculated attribute derived from other attributes within the same entity
derived attribute
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is the process of creating a visual representation of an information system to communicate the connections between data points and structures.
data modeling
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where many instance of an entity are associated with many instance of other entity is also called many to many relationship
non-specific relationship
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Data entity that contributes one or more attribute to other entity
parent entity
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Entity that derives one or more attributes from other entity
child entity