Current Version - Under Revision
Some Concepts have a large number of subtype children that cannot be logically divided into intermediate subtypes. At the user interface these result in long lists of options, which are difficult to visualize and navigate. Navigational Concepts with appropriate navigational links to the supertype parent and its subtype children provide an intermediate layer without disrupting the semantic definitions.
Some Concepts that are members of the same rational set of choices may be found at different levels in the subtype hierarchy. This may occur because some have intervening subtypes and some of these intervening concepts may not be required for data entry. Addition of new concepts in a release may change the concepts available at some levels in the subtype hierarchy. Navigation links can "bypass" levels in the subtype hierarchy to represent a rational sets of choices for use in a particular situation.
While it is semantically correct to nest 82272006 |common cold| in the following subtype hierarchy, a user may reasonably expect to see "common cold" as an immediate navigational child of 54150009 |upper respiratory infection|.
A navigation links could associate:
Vertebrae, cranial nerves, disease stages, etc.
The subtype hierarchy is logically defined and there can only be one such hierarchy. However, as navigation hierarchies have no definitional consequences, it is possible to have different hierarchies for different groups of users with differing needs.
Initial releases of SNOMED CT will contain a single set of navigation links but those engaged in technical implementation should be aware that in the future there may be separate sets of navigation links for use in different environments.