, , .
, , . .
ER-. -, , R-. -, , .
(C) , , /.
"/". . , . " " (1:1). . , . Manager Sales_Personnel. Staff. - - , , - .
() . Staff, (NULL) , .
, (), . , Sales_Personnel , , Re-quires () Sales Personnel Car ().
, , , , . , Sales Personnel Staff (.. Staff-No, Name, Address ), Sales=Personnel (.. Car_Allowance Sales_Area).
, o. , , - (type hierarchy). : (specialization hierarchy) - , Manager Staff; (generalization hierarchy) - , Staff Manager; (IS-A hierarchy) - , ( Manager) ( Staff).
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( ), , ( ).
, RR- , . , Manager Branch Manages, Staff Branch IsAllocated.
(shared subclass). (multiple inheritance).
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- , .
(disjoint) "d", , .
(Full_Time_Permanent Part_Time_TempOrary) . , , .
, . (nondisjoint) "", , . (Manager, Secre-tary, Sales_rsnnl) . , (.. Manager), (.. Sales_Personnel).
(participation constraint), . , . . , .
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, . . , , - (.. Manager), (.. Secretary) (.. Sales _personnel).
, .
"/", . (category).
Property_owner , Person Business. Property , , Property_for_Sale Property_for_Rent. , - , (C), (U).
/, . , , - . , , - .