| abt weak entities [message #115339] |
Sat, 09 April 2005 18:37 |
himoundary
Messages: 1
Registered: April 2005
Location: india
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Junior Member |
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i wanna kno wot exactly is a weak entity. i hav seen 2 defs in various places:
1) a weak entity is one which is dependent for its existence on some other entity
2) a weak entity is one which needs the primary key of some other entity as part of its primary key (i.e. it needs the primary key of some other entity to be uniquely identified).
now, wot i wanna kno is that r both these conditions essential for an entity to be weak? consider the typical employee - dependent relationship; here the dependent will not (cannot) exist without a corresponding employee, but still i may assign it a unique key dep_id (which is automatically generated by a sequence whenever a dependent record is addded). the primay key of the employee will still be present in the attributes of the dependent but only as a foreign key (and not necessarily as part of the primary key as required by def 2).
so in dis case, is dependent a weak entity or not?
or m i really confusing some concepts? plz help.
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