OntoClean is a methodology for validating the ontological adequacy
of taxonomic relationships. It is based on highly general ontological
notions drawn from philosophy, like essence, identity, and unity,
which are used to characterize relevant aspects of the intended meaning
of the properties, classes, and relations that make up an ontology.
These aspects are represented by formal metaproperties, which impose
several constraints on the taxonomic structure of an ontology. The
analysis of these constraints helps in evaluating and validating
the choices made. In this chapter we present an informal overview
of the philosophical notions in- volved and their role in OntoClean,
review some common ontological pitfalls, and walk through the example
that has appeared in pieces in previous papers and has been the basis
of numerous tutorials and talks.