. Author manuscript; available in PMC: 2008 Jul 2.

Published in final edited form as: Artif Intell Med. 2007 Jan 22;39(3):183–195. doi: 10.1016/j.artmed.2006.12.003

Table 5.

Ontological principles studied in SNOMED CT

P1	Each class must have at least one parent
P2	Non-leaf classes must have at least two children
P3	Children should have exactly one parent
P4	Each hierarchy must have a single root
P5	Each child’s description must differ from its parent’s description
P6	All roles of a parent class must either be inherited by each child or refined in the child
P7	Differentia from child to parent should uniquely result in every case either from refinement of the value of a common role or introduction of a new role