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2-4 DATA MODELING TERMINOLOGY (SUPERTYPE & SUBTYPE ENTITIES (Subtype…
2-4 DATA MODELING TERMINOLOGY
TERMINOLOGY MAPPING
ERD -> Physical Design
Entity -> Table
Instance -> Row
Attribute -> Column
Primary UID -> Primary Key
Secondary UID -> Unique Key
Relationship -> Foreign Key
ENTITIES
"Something" of significance to the business about which data must be known
P
Prime = Exists independently
C
Characteristics = Exists because of another entity
I
Intersection = Exists because of 2 or more entities
ATTRIBUTES
Provide
more specific info about an entity
Help
distinguish between 1 instance and another by providing greater detail for the entitity
?
D
DESCRIBE an entity
Q
QUANTIFY an entity
C
CLASSIFY an entity
SUPERTYPE & SUBTYPE ENTITIES
Supertype has a
parent-child
relationship with 1 or more subtypes
Subtype is a
subgrouping
of the entity in an entity type
GENERALIZATION
Bottom-up
approach where 2 or more lower level entities are combined to form a higher level entity based on common features
SPECIALIZATION
Top-down
approach where he higher level entity is broken down into lower level entities
Subtype RULES
E
EXHAUSTIVE = Every instance of a supertype is also an instance of one of the subtypes
ME
MUTUALLY EXCLUSIVE = Every instance of the supertype is of one and only one subtype. Eg, an employee cannot be both full time and part time