1. Introduction Materials & methods Results Conclusion
Redundant Elements in SNOMED CT
Concept Definitions
Kathrin Dentler and Ronald Cornet
31. May @ AIME 2013. Paper: http://www.few.vu.nl/~kdr250/
publications/AIME2013-Redundant-Elements-SNOMED.pdf
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 1/23

2. Introduction Materials & methods Results Conclusion
Outline
1 Introduction
2 Materials & methods
3 Results
4 Conclusion
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 2/23

3. Introduction Materials & methods Results Conclusion
SNOMED CT
Systematized Nomenclature Of Medicine Clinical Terms
Meaning-based recording & retrieval, reuse,
interoperability!
Most comprehensive clinical terminology: around 300,000
concepts
Concepts are organized in hierarchies with multiple levels
of granularity
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 3/23

4. Introduction Materials & methods Results Conclusion
SNOMED CT
Systematized Nomenclature Of Medicine Clinical Terms
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 4/23

5. Introduction Materials & methods Results Conclusion
SNOMED CT Concept Definitions in EL+
RoleGroups
Finding X includes an inflamed arm and a broken leg:
∃Finding site.Arm
∃Associated morphology.Inflammation
∃Finding site.Leg
∃Associated morphology.Fracture
→unclear what belongs together. Therefore, role-value pairs
can be grouped in RoleGroups (RG):
∃RG(Finding site.Arm
Associated morphology.Inflammation)
∃RG(Finding site.Leg Associated morphology.Fracture)
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 5/23

6. Introduction Materials & methods Results Conclusion
SNOMED CT Concept Definitions in EL+
Conjunctions ( ) of other concepts (superconcepts) and
role-value pairs (∃), ungrouped or grouped in RoleGroups.
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 6/23

7. Introduction Materials & methods Results Conclusion
(Intra-Axiom) Redundancies
Redundant element
Stated explicitly even though it is implied by the
definition of the same concept or a stated superconcept.
Can be removed without affecting the logical closure.
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 7/23

8. Introduction Materials & methods Results Conclusion
(Intra-Axiom) Redundancies
Confuse knowledge modellers (Spackman; Chief
Terminologist at IHTSDO)
Make a terminology less flexible and harder to maintain
(Grimm and Wissmann)
Should be recognized & rendered transparent (Cimino)
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 8/23

9. Introduction Materials & methods Results Conclusion
(Intra-Axiom) Redundancies
Example
Example: Two concepts July 2012
Non-imaging thyroid uptake test
Radionuclide study of endocrine function
∃RG(∃Method.Radionuclide imaging
∃Procedure site.Thyroid structure
∃Using substance.Radioactive isotope)
Thyroid uptake with thyroid stimulation
Stimulation test Non-imaging thyroid uptake test
Radionuclide uptake study
∃RG(∃Method.Radionuclide imaging
∃Procedure site.Thyroid structure
∃Using substance.Radioactive isotope)
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 9/23

10. Introduction Materials & methods Results Conclusion
(Intra-Axiom) Redundancies
Might lead to content-related problems when concepts drift
Example: Two concepts January 2013
Non-imaging thyroid uptake test
Radionuclide study of endocrine function
∃RG(∃Method.Radionuclide imaging
∃Procedure site.Thyroid structure
∃Using substance.Radioactive isotope)
Thyroid uptake with thyroid stimulation
Stimulation test Non-imaging thyroid uptake test
Radionuclide uptake study
∃RG(::::::::::::::::::::::::::::::::
∃Method.Radionuclide imaging
∃Procedure site.Thyroid structure
∃Using substance.Radioactive isotope)
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 10/23

11. Introduction Materials & methods Results Conclusion
Approach
Spackman: defined rules to determine and eliminate
redundant expressions in concept definitions (2002)
We adapted and extended these rules; one rule per
element:
1 concepts
2 ungrouped exists restrictions
3 exists restrictions within rolegroups
4 rolegroups
Aim: apply the rules to the entire SNOMED CT; support
knowledge modellers
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 11/23

12. Introduction Materials & methods Results Conclusion
Four rules of redundancy detection
Concept
A concept is redundant when it is more general than or
equivalent to another concept in the definition of the same
concept or a superconcept.
Example: Structure of lobe of brain
Structure of lobe of brain
Brain part Brain tissue structure
Brain tissue structure Brain part
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 12/23

13. Introduction Materials & methods Results Conclusion
Four rules of redundancy detection
Ungrouped exists restriction
An ungrouped exists restriction is redundant when it is more
general than or equivalent to another ungrouped exists
restriction within the definition of the same concept or a
superconcept.
Example: Parenteral form thymoxamine
Thymoxamine (product)
Alpha blocking vasodilator Alpha 1 blocking agent
∃Has active ingredient.Thymoxamine (substance)
Parenteral form thymoxamine (product) ≡
Thymoxamine (product)
∃Has active ingredient.Thymoxamine (substance)
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 13/23

14. Introduction Materials & methods Results Conclusion
Four rules of redundancy detection
Exists restriction within rolegroup
An exists restriction is redundant within a rolegroup when it is
more general than or equivalent to another exists restriction in
the same rolegroup.
Example: Closed skull fracture with intracranial injury
Closed skull fracture with intracranial injury ≡
Fracture of skull
∃RG(∃Finding site.Intracranial structure
∃Associated morphology.Traumatic abnormality
∃Associated morphology.Closed traumatic abnormality )
Closed traumatic abnormality Traumatic abnormality
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 14/23

15. Introduction Materials & methods Results Conclusion
Four rules of redundancy detection
Rolegroup
A rolegroup is redundant when all its exists restrictions are
more general than or equivalent to those contained in another
rolegroup in the definition of the same concept or a
superconcept.
Example: Brain stem contusion with open intracranial wound
Brain stem contusion with open intracranial wound ≡
Contusion of brain with open intracranial wound
∃RG(∃Associated morphology.Open wound
∃Finding site.Intracranial structure)
∃RG(∃Associated morphology.Open contusion
∃Finding site.Brainstem structure)
Open contusion Open wound
Brainstem structure Intracranial structure
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 15/23

16. Introduction Materials & methods Results Conclusion
Four rules of redundancy detection
Approach
Applied the four rules of redundancy detection to each
concept and recursively all its stated (direct and indirect)
superconcepts in the stated form of SNOMED CT.
Eliminated all identified redundant elements.
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 16/23

17. Introduction Materials & methods Results Conclusion
Detected redundancies
Applying the four rules of redundancy detection, 35,010 of the
296,433 SNOMED CT concepts (12%) were identified to
contain redundant elements in their definitions.
Overview of all identified redundant elements:
Rule All Percentage
rolegroup 50,680 41%
ungrouped exists restriction 13,808 54%
concept 842 0.024%
grouped exists restriction 6 0.00026%
Sum 65,336
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 17/23

18. Introduction Materials & methods Results Conclusion
Categories of concepts with redundancies
finding
procedure
product
body structure
situation
specimen
organism
substance
physical object
Number of Concepts
0
5000
10000
15000
20000
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 18/23

19. Introduction Materials & methods Results Conclusion
Distances
Defined as steps in the concept hierarchy
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 19/23

20. Introduction Materials & methods Results Conclusion
Evaluation of Results
Partial completeness by comparison to Cornet and Abu-Hanna
Cornet and Abu-Hanna (2008) designed a method to identify
underspecified concepts, which can also identify special cases
of redundantly defined concepts.
→We compare the results of the two methods.
Partial completeness: All redundantly defined concepts
identified by applying the Cornet and Abu-Hanna method
must also be identified by the application of the four rules of
redundancy detection.
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 20/23

21. Introduction Materials & methods Results Conclusion
Evaluation of Results
Partial completeness by comparison to Cornet and Abu-Hanna
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 21/23

22. Introduction Materials & methods Results Conclusion
Evaluation of Results
Soundness
Closure of manipulated, redundancy-free version of SNOMED
CT equivalent to closure of original version.
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 22/23

23. Introduction Materials & methods Results Conclusion
Questions?
Overview of redundant
elements in SNOMED CT
Rules could help to
remove existing
redundancies and to
prevent future
redundancies
advantage: explanations!
IHTSDO: redundancy-free
normal forms
Future: Generalisation of
method
Kathrin Dentler and Ronald Cornet — Redundant Elements in SNOMED CT Concept Definitions 23/23