| The Object | Relational Gap | 
       | transient | persistent | 
       | classes | tables | 
       |  |  | 
       | attributes | columns | 
       | objects | rows | 
       | 
instance attributeimplicity ID: reference   | 
fieldexplicit ID: primary key   | 
       | relations | relations | 
       | 
referencesunidirectional ordered (lists)   | 
foreign keysbidirectional   | 
       | behaviour centric | data centric | 
       | 
navigate to objectbehaviour based partitioningmethods   | 
operate on setrelation based partitioningstored procedures   | 
       | 
tight behaviour-data coupling 
 |  | 
       | 
data hiding, encapsulation 
 | 
 | 
       | 
 |  | 
 
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