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26 Cards in this Set
- Front
- Back
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ERM
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entity relationship model
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entities
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an object of interest to an end user
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ERM entity
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table
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entity instance
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row
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attribute
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characteristic of entity, field
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required attribute
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must have a value. a NOT NULL column
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optional attibute
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field that does not require a value
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attribute domain
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the list of possible values for a field. (Y,N) or (M,F)
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identifier
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primary key. one or more attributes that identify an entity instance
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composite identifier
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primary key with multiple values.
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composite attribute
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attribute that envelops sub attributes. ADDRESS contains STREET & CITY etc
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multivalued attributes
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an attribute that can have many values, a person can have many degrees
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derived attributes
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calculated, FULNAME = FIRST + LAST
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participants
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entities that participate in a relationship
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relationship
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association between entities, a verb, STUDENT takes CLASS.
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entity relationship
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one to one, one to many, or many to many
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connectivity
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describes relationship classification
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cardinality
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the amount of rows in a table.
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existence-dependent
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must have a dependent attribute, a foreign key for example
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weak relationship
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relationship with foreign key only
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strong relationship
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relationship between two tables with field in both primary keys
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weak entity
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requires a parent table. it's primary key is derived from the parent
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optional participation
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a table is independent of the other in the relationship
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mandatory participation
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a table is dependent on the other's data in a relationship
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recursive relationship
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relationship between rows in same table
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iterative process
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looping, repetitive
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