• What's that: it's grey and as a trunk (german: "Rüssel") ?

make implicit relations explicit

  • X isUncleOf Y <- X isBrotherOf Z and Z isParentOf X

conformity of a single data record w.r.t. a schema

  • is the value given for attribute "startsWith" a valid xsd:dateTime object?
  • is it ok for an instance of the class "male" to be married to another instance of the class "male"?

consistency of a complex fact base w.r.t. a schema (resp. a set of integrity constraints)

  • A battery must be able to provide a stable currency for all consumers
  • A person P may be considered being an expert on a subject S only if she is author of a scientific publication concerning S

expansion of search queries

  • a search for animals expands to a search also for dogs, cats etc.

subsume knowledge

  • an article about african lions is subsumed under the class of documents about animals

database integration

  • an instance of the class person in database D1 is mapped to an instance of class author in database D2 iff this person is author of a scientific publication

make implicit knowlege explicit by means of communicating understandings of a terminology

  • ontologies always should be comprehensible by more than one person
  • an ontology which isn't comprehensible won't be accepted in practice!