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Breaking down a subtype into manageable categories

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.

The 404684003 |clinical finding| top-level Concept has a large number of subtype children. Intermediate navigation Concepts group some of these together in a convenient way.


Three subtypes related to pregnancy are grouped together under a single natural navigational Concept :

  • Disorder of pregnancy / labor / delivery / puerperium [ navigation concept ];
  • Disorder of pregnancy;
  • Disorder of labor / delivery;
  • Disorder of puerperium.

Bypassing levels in the subtype hierarchy

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|.

Linking related Concepts of different types

Navigational links can also be used to provide access to connected Concepts even when they are from different hierarchy branches.


A navigation links could associate:

Ordering the display of subtypes

Sibling Concepts in a subtype hierarchy are not ordered. However, at the user interface a particular order may be useful to highlight commonly used Concepts or to mirror a conventional ordering.


Vertebrae, cranial nerves, disease stages, etc.

Navigational links are ordered and are used to impose order, even when the set of navigational children is the same as the set of subtype children.

Providing alternative hierarchies

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.