SNOMED CT® Release Format 1 (RF1) Guide - ihtsdo

338 | SNOMED CT Release Format 1 (RF1) Guide July 2012
The existence of multiple Descriptions containing exactly the same Term but linked to different Concepts
does not cause any technical problems but may cause confusion at the user interface. The appearance of
several identical phrases in a search list presents a dilemma and applications need to present sufficient
information to allow the user to choose between them. In most cases this requires the application to provide
a view of the Fully Specified Names associated with any Duplicate Terms.
The Duplicate Terms Subset, part of the SNOMED CT Developer Toolkit, is intended to assist applications
to identify and manage the presentation of Duplicate Terms by:
• Identifying the Duplicate Terms in a particular release of SNOMED CT.
This simplifies the processing required to determine if a duplicate exists and will require disambiguation.
• Indicating a priority between Duplicate Terms.
Applications may use these priorities to support sensible display ordering or default selection.
The Duplicate Terms Subset is Language and Dialect dependent since the occurrence of and priorities
between duplicates will vary according to the applicable set of Terms specified in a Language Subset. In
addition, specialty or user specific priorities may be applied by alternative Duplicate Terms Subsets derived
from the distributed files.
• Each current Description containing a Term that is also present in another current Description is a member
of the Duplicate Terms Subset;
• The Subset Member has a status that indicates its priority;
• The LinkedID refers to the Description which contains the same Term and has the highest priority.
This reference links together a set of Descriptions which contain the same Term.
4.4.3.5.5. Specifying "natural" display orders
The formal subtype Relationships of SNOMED CT are specified as logical definitions.These provide a powerful
tool for organizing , retrieving and aggregating data. These subtype Relationships can also be used for
Navigation to locate a more or less specific Concept. However, the requirements for Navigation differ from
those for logical definition. The following factors affect the efficiency of Navigation but have no relevance to
logical definitions of Concepts:
• Frequency of use of Concepts and their relative accessibility.
• Depth of nesting of a hierarchy
• Length of a displayed hierarchy level.
• Order of listed Concepts:
• Matching a natural order (e.g. cranial nerves, cervical vertebrae, etc.).
• Reflecting frequency of use.
• User association of ideas that are not linked as subtypes of one another.
The Relationships Table does not specify the order in which Relationships should be displayed and places
no limits on the size or depth of any hierarchy. There are several reasons for this:
• The display order of many Relationships is arbitrary.
• Different display orders may be appropriate to the same Relationships depending on user preferences
and the context.
• The display order of Relationships is not fundamental to an understanding of the related concepts. A
change in display order does not alter the meaning of a Concept. Therefore, it need not be subject to the
rigorous change control applied to the core tables.
There is a requirement for one or more Navigation hierarchies, which are configurable without undermining
the logical definitions of SNOMED CT.
The Subset mechanism includes Navigation hierarchies, which allow a natural or preferred display order to
be defined for a set of Navigation Links. They are represented as follows:
© 2002-2012 International Health Terminology Standards Development Organisation CVR #: 30363434