Excerpt from home page: Generic model derived from RDF Schema (which in turn was derived from CycL, which in turn ...). We have a set of types, arranged in a multiple inheritance heirarchy where each type may be a sub class of multiple types. We have a set of properties each property may have one or more types as its domains. The property may be used for instances of any of these types. each property may have one or more types as its ranges. The value(s) of the property should be instances of at least one of these types. The decision to allow multiple domains and ranges was purely pragmatic.