CIDOC CRM
The CIDOC object-oriented Conceptual Reference Model (CRM) is an ontology for describing concepts and information in cultural heritage. It's primary use-case seems to be museums and scholarly research in cultural heritage.
Overview
CIDOC CRM describes itself as "object-oriented" in the sense that entities are instances of abstract classes that may be decorated with pre-defined predicates. CIDOC CRM is a hierarchy of classes and properties.
Some example classes are:
E22 Man Made ObjectE666 Formation(an entity that describes the event that results in the formation of something)
Some example predicates are:
P2 has typeP122 borders with
In total 90 classes and 149 predicates are defined by CIDOC CRM.
CIDOC CRM is open in the sense that it is extensible. New entities/classes can be defined as sub-classes for specific applications.
Compared to the Resource Description Framework (RDF)
The organization of classes and predicates is similar to how RDF works. In fact there is a mapping of CIDOC CRM to RDF: Erlangen CRM.
RDF is more generic and abstract. Basic classes and types, semantics and composability of various ontologies are defined by RDF itself. Domain specific ontologies and vocabularies can be defined using RDF and be used inter-operably. CIDOC CRM defines everything itself and thus is not interoperable with other ontologies.
Historically it seems that CIDOC CRM was developed and defined (2000-2006) around the same time that RDF was initially developed (1999-2004). The author suspects that if CIDOC CRM would have been developed a few years later it would have been defined as an RDF ontology - like DDI-RDF Discover Vocabulary (Disco) or PREMIS Data Dictionary for Preservation Metadata.
In 2023 it seems better to use a natively RDF based ontology (such as DISCO or PREMIS) to describe the same conceptual information that CIDOC CRM was designed to capture.