However: Ontologies are Hard!
Hard to implement a full ontology management system
may be superfluous for some applications
Hence the “onion” model of increasingly complex specs:
no property expressions or datatypes in RDF Schemas
not all set operators, restricted cardinality in OWL Lite
full expressive power in OWL Full (no computational guarantee)
classes can themselves be instances
classes of properties can be defined
statements on properties are possible
“Lite” < “DL” < “Full”, but not completely true for RDFS
RDFS is “almost” a subcategory
not all RDFS statements are valid in DL…
…but they are for Full
Applications may take what they really need!
Ivan Herman
, W3C Head of Offices
Madrid, 22 October, 2003
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