However: ontologies are hard!

• A full ontology-based application is a very complex system

• Hard to implement, may be heavy to run…

• … and not all applications may need it!

• Three layers of OWL are defined: Lite, DL, and Full

• • decreasing level of complexity and expressiveness
  • • “Full” is the whole thing
    • “DL (Description Logic)” restricts Full in some respects
    • “Lite” restricts DL even more