ch3+4 Flashcards
enhanced ER model
enhanced ER model
modifications to ER model from the 70s. more like object oriented. enables more complex data arrangement
subtype
subgrouping of the entities that is meaningful to organization. inherit attributes from supergroup AND have its own unique attributes
EER notation
subtype > circle > U shape
attribute inheritance
contain all attributes of supertypes up the chain
outpatient
patient in hospital for less than 24 hours
generalization
develop more general entity types from set of more specialized ones. bottom up process
specialization
top-down process to create subtypes
completeness constraint
addresses question of whether supertype can be a member of subtype. two types: total specialization and partial specialization
total specialization
rule that specifies EVERY entity instance of supertype is also a member of some subtype.indicated by double line to the circle
partial specialization
supertype does not have to fit into one of the subtypes
disjointness constraint
addresses whether supertype can be more than one subtype. two rules: disjoint or overlap
disjoint rule
supertype may cannot be more than one subtype. symbolized by “d” in circle
overlap rule
instance of supertype may be in more than one subtype, symbolized by “O” circle
subtype discriminator
attribute code of supertype that determines target subtype(s)
supertype/subtype hierarchy
hierarchical arrangement in which subtype only has one supertype
