Answer Posted / meena
A surrogate key in a database is a unique identifier for
either an entity in the modeled world or an object in the
database. The surrogate key is not derived from application
data.
There appear to be two definitions of a surrogate in the
literature. We shall call these surrogate (1) and surrogate
(2):
Surrogate (1) This definition is based on that given by
Hall, Owlett and Todd (1976). Here a surrogate represents
an entity in the outside world. The surrogate is internally
generated by the system but is nevertheless visible by the
user or application.
Surrogate (2) This definition is based on that given by
Wieringa and de Jung (1991). Here a surrogate represents an
object in the database itself. The surrogate is internally
generated by the system and is invisible to the user or
application.
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