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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
- Applications may take what they really need!
