E55 Type in Version 4.1

This class comprises arbitrary concepts (universals) and provides a mechanism for organising them into a hierarchy.

This hierarchy is intended to duplicate the names of all the classes present in the model. This allows additional refinement, through subtyping, of those classes which do not require further analysis of their formal properties, but which nonetheless represent typological distinctions important to a given user group.

It should be noted that the Model does not make the distinction between classes and types known from some knowledge representation systems and object-oriented programming languages. The class E55 Type can be regarded as a metaclass (a class whose instances are universals), used to denote a user-defined specialization of some class or property of the Model, without introducing any additional formal properties for this specialization.

It reflects the characteristic use of the term “object type” for naming data fields in museum documentation and particularly the notion of typology in archaeology. It has however nothing to do with the term “type” in Natural History (cf. E83 Type Creation), but it includes the notion of a “taxon”.

Ideally, instances of the class E55 Type should be organised into thesauri, with scope notes, illustrations, etc. to clarify their meaning. In general, it is expected that different domains and cultural groups will develop different thesauri in parallel. Consistent reasoning on the expansion of subterms used in a thesaurus is possible insofar as it conforms to both the classes and the hierarchies of the model.

E56 Language, E57 Material and E58 Measurement Unit have been defined explicitly as elements of the E55 Type hierarchy because they are used categorically in the model without reference to instances of them, i.e. the Model does not foresee the description of instances of instances of them, e.g., the property instance “P45 consists of : gold” does not refer to a particular instance of gold.