|  | 
| ontology | + class expressions, etc. | KIF, DAML+OIL, OWL | 
| data model | + abstraction | UML | 
| database schema | + relations between objects | RDBMS, OODBMS | 
| class hierarchy | + attributes | C++, Java, CORBA IDL | 
| taxonomy | subclass relationships | biology | 
| directory | grouping of related items | yahoo.com | 
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