A marker class that can be attached to base URIs (ontologies) to instruct SPIN engines that this ontology only contains a library of SPIN declarations. Library Ontologies should be ignored by SPIN inference engines even if they have been imported by a domain model. For example, a SPIN version of OWL RL may contain all the OWL RL axioms, attached to owl:Thing, but nothing else. However, when executed, these axioms should not be executed over themselves, because we don't want the system to reason about the SPIN triples to speed up things.