SNOB - A SNOMED Browser

SNOMED CT MetaModel - background

Ontologies such as SNOMED CT and OpenGALEN require some system of constraints - often called a MetaModel - that prevent nonsense combinations of concepts and relationships. For example, it would be desirable to prevent users entering obviously nonsense expressions such as:

Monkey (organism):method (attribute)=repair (action)

or

Bony fracture (morphological abnormality):
  finding site (attribute)=eyebrow (body structure),
  causative agent (attribute)=cheese (substance)

Systems to prevent such nonsense are typically comprised of many layers of constraints, of which the most general layer is designed to prevent what are sometimes called major category errors.

SNOMED CT's list of major category error constraints is generally referred to as its Concept Model. This currently appears in human-readable form only, distributed principally between Appendix J of the Technical Reference Guide (which contains separate tables of domain and range constraints on individual attributes) and the User Guide, although these two sources are not entirely consistent with one another.

In recognition of these shortcomings, the IHTSDO has identified as an urgent activity the development of a machine readable concept model.

For experimental purposes, SNOB currently implements one possible form of a MetaModel, in which the constraints are expressed not as independent domain and range constraints on an individual attribute, but as constraint triples in which the allowed range for an attribute is different depending on the domain context, and vice versa.