Appendix D: Concept Definition Illustrations
A concept definition is a set of one or more axioms that partially or sufficiently specify the meaning of a SNOMED CT concept.
Notes
Concept definitions are represented in two ways in SNOMED CT release files: * As a stated view represented by axioms that conform to the OWL Functional Syntax distributed in the OWL Expression Reference Set file. * As an inferred view represented by defining relationships that are distributed in the relationship file. The inferred view is generated by applying description logic classification to the stated view.
Concept definitions include two distinct elements
Axioms that assert that a concept is a subtype of one or more other concepts. In the inferred view these are represented as subtype relationships.
Axioms that assert characteristics of a concept that distinguish it from its supertypes. In the inferred view these are represented as attribute relationships.
This appendix illustrates some of the features of concept definitions outlined in section Concept Definitions.
Stated and Inferred Definitions - Examples
The appendix contains an extended version of Stated and Inferred Concept Definitions supported by more detailed examples.
Stated View of Concept Definitions
SNOMED CT concepts are defined by assertions made by SNOMED CT authors. The concept definitions asserted by SNOMED CT authors are known as the stated view.
The stated view is a representation of concept definitions consisting only of assertions made or revised by SNOMED CT authors.
Notes
In contrast to the inferred view, the stated view does not include inferences generated by applying a description logic classifier.
The stated view is represented by axioms, that conform to the OWL functional syntax. These axioms are distributed in the OWL axiom reference set file.
Description Logic Classification
A description logic classifier can apply logical rules to the stated view to create inferences. The end result of this process is an inferred view of concept definitions.
Inferred Views of Concept Definitions
The inferred view is a representation of concept definitions that is logically derived by applying a description logic classifier to the stated view.
Notes
Different inferred views can be derived from the same stated view by applying different rules that selectively exclude some types of assertions.
Different inferred views may be semantically equivalent to one another provided that assertions are only excluded if they are redundant (i.e. can be inferred from assertions that are included). However, in some cases, an inferred view may not completely represent the concept definition but may serve a specific purpose.
Illustration of the Effect of Classification
Table D.1-1 shows the stated view of the definitions of 710785000 |Laparoscopic repair of hernia| . Compare this with the inferred view of the same concept in Table D.1-2 and you can see that the single supertype concept 71388002 |Procedure| been replaced by four supertype concepts in the inferred view.
The classifier has compared the definition of 710785000 |Laparoscopic repair of hernia| with the concept definitions shown in Tale D.1-3 and determined that 710785000 | Laparoscopic repair of hernia| is a subtype of all these concepts.
In fact, the classifier will also have found several other supertypes but the inferred view distributed in the relationship file only includes proximal supertypes (parents). Other supertype ancestors are excluded from the file because they are redundant.1
Stated view of the definition of |Laparoscopic repair of hernia|
Inferred view of the definition of the concept |Laparoscopic repair of hernia|
=== 363321000 |Surgical repair procedure by device| + 50465008 |Hernia repair| + 51316009 |Laparoscopic procedure| + 264274002 |Endoscopic operation| : { 363700003 |Direct morphology| = 414402003 |Hernial opening (morphologic abnormality)| , 425391005 |Using access device| = 86174004 |Laparoscope, device| , 260686004 |Method| = 257903006 |Repair - action| }
Stated views of the four supertype concepts in the inferred |Laparoscopic repair of hernia|
A supertype in the two definitions above
363687006 | Endoscopic procedure|
A supertype in the definition above
The information in this section is particularly relevant to those wishing to understand the changes made to enhance the representation of stated concept definitions between July 2018 and 2019. The stated relationships file is no longer maintained and distributed. From July 2019 it was replaced by the OWL Expression Reference Set file.
Necessary and Sufficient - Examples
The appendix contains an extended version of Necessary Conditions and Sufficient Definitions supported by more detailed examples.
Assertions
The stated view of concept definition consists of one or more assertions made by SNOMED CT authors.
Necessary Conditions
Each time an assertion is made about a concept, an author must decide if that assertion is a necessary condition. If the assertion is always true for that concept and its subtypes, it is a necessary condition.
This implies that for all instances of that concept or its subtypes, the assertion must be true, even if it has not been explicitly stated.
A necessary condition is defined as a characteristic that is always true of a concept.
Example
If you have a 71620000 |fracture of femur| , the morphological abnormality 72704001 |fracture| must be present. Therefore, 116676008 |morphology| = 72704001 |fracture| is a necessary condition of 71620000 |fracture of femur| .
Sufficient Definitions
For each concept an author must decide if there are one or more sets of assertions that form a sufficient definition of that concept. A set of assertions is a sufficient definition if it distinguishes a concept and its subtypes from other concepts.
This implies that if all assertions in the set are true for a concept, it must be an instance of the defined concept or a subtype of that concept.
A sufficient definition is a set of characteristics which distinguish a concept and its subtypes from all other concepts.
Notes
Any concept that matches the sufficient definition is equivalent to or a subtype of the defined concept.
A concept may have more than one sufficient definition. In that case any concept that matches at least one of these sufficient definitions is equivalent to or a subtype of the defined concept.
Examples
The following set of assertions is a sufficient definition for 74400008 |appendicitis (disorder)| because any concept for which this set of assertions is true must either be the disorder appendicitis or a subtype of appendicitis.
Both the following sets of assertions are sufficient definitions for the concept 8801005 |Secondary diabetes mellitus (disorder)| :
73211009 |Diabetes mellitus| : 246075003 |Causative agent| = 105590001 |Substance|
73211009 |Diabetes mellitus| : 42752001 |Due to| = 64572001 |Disease|
While each of the assertions 246075003 |Causative agent| = 105590001 |Substance| and 42752001 |Due to| = 64572001 |Disease| form part of a sufficient definition, neither of these assertions are necessary conditions because only one of them needs to be true. This illustrates that an assertion that is part of a sufficient definition need not be a necessary condition.
Concepts with no Sufficient Definitions
A concept that has no sufficient definitions is a primitive concept.
Because primitive concepts have no sufficient definitions it is not possible for a description logic classifier to determine if other concepts are subtypes of this concept. Similarly, it is not possible to automatically determine whether an expression is a subtype of a primitive concept. Therefore, only concepts or expressions that explicitly state they are subtypes of primitive concepts will be treated as subtypes when applying expression constraints or undertaking analysis.
However, note that this does not prevent a primitive concept being classified as a subtype of a sufficiently defined concept.
Concepts with a Sufficient Definition
A concept that has at least one sufficient definition is a sufficiently defined concept.
A description logic classifier can determine whether the stated definitions of other concepts meet at least one of the sufficient definitions and if so will classify these concepts as its subtypes. Similarly, it is possible to determine whether an expression is equivalent to or a subtype of a sufficiently defined concept. Therefore, where expression constraints or queries refer to sufficiently defined concepts the results will include the inferred subtypes of these concepts.
Sufficiently Defined Concepts with Necessary Conditions
If a sufficiently defined concept has one or more additional necessary conditions then any concept or expression that satisfies one of its sufficient definitions will also inherit any necessary conditions.
For example one sufficient definition of 397825006 |Gastric ulcer (disorder)| is an ulcer in a stomach structure:
=== 64572001 |disease| : { 116676008 |associated morphology| = 56208002 |ulcer| , 363698007 |finding site| = 69695003 |stomach structure| }
However, another definition could be created with a more specific site gastric mucosa:
=== 64572001 |disease| : { 116676008 |associated morphology| = 56208002 |ulcer| , 363698007 |finding site| = 78653002 |gastric mucosa| }
In both cases these definition are equivalent to 397825006 |Gastric ulcer (disorder)| . The more general definition is flexible when it comes to allowing refinement to a specific location of the ulcer within the stomach, which is actually useful information. It also avoids requiring an expression to refer specifically to the mucosa (stomach lining), which is where all gastric ulcers occur.
For example, an expression including the specific location could look like this
=== 64572001 |disease| : { 116676008 |associated morphology| = 56208002 |ulcer| , 363698007 |finding site| = 127869006 |Anterior wall of fundus of stomach| }
This satisfies the sufficient definition because the finding site is a subtype of stomach structure. This will therefore classify as a type of 397825006 |Gastric ulcer (disorder)| located in the anterior wall of the gastric fundus. The problem is that a query for disorders of the gastric mucosa will not find this expression. << 64572001 |disease| : 363698007 |finding site| = 78653002 |gastric mucosa| However, adding the definition that refers to the gastric mucosa as an additional necessary condition can solve this problem. The expression satisfies the sufficient definition implying this is a type of 397825006 |Gastric ulcer (disorder)| . The fact that it is a type of gastric ulcer causes it to inherit 363698007 |finding site| = 78653002 |gastric mucosa| so it will now be included in the query for disease in the gastric mucosa.
A Definition that is Both Necessary and Sufficient
The definition shown in Table D.2-1 provides an example of a simple case.
The === symbol indicates that the concept definition is equivalent to the concept.
This means that each of the assertions in the definition is necessarily true for all instance of the concept 710785000 |Laparoscopic repair of hernia| .
It also means that this definition is sufficient , because if all the assertions are true, this implies this is either the concept or a subtype of the concept.
Table D.2-1: Stated view of the definition of |Laparoscopic repair of hernia|
A Definition that is Necessary but Not Sufficient
The definition shown in the Table below provides an example of another simple case.
The <<< symbol indicates that the concept is a subtype of the concept definition.
This means that each of the assertions in the definition is necessarily true for all instance of the concept 173574009 |Acute benign pericarditis (disorder)| .
However, this definition is not sufficient , because it is represent a more general meaning. Put another way, it does not capture one or more distinguishing features or the 173574009 |Acute benign pericarditis (disorder)| . This means that even if all the assertions are true, it may or may not be this concept or one of its subtypes.
Stated view of the definition of |Acute benign pericarditis|
A Definition that is Sufficient with Assertions that are Not Necessarily True
This example illustrates a type of definition that was not supported prior to the enhancement to SNOMED CT support for advanced description logic. Therefore, the definition shown is for illustration only and will not be found in current releases of SNOMED.
The definition shown in the Table below provides an example of a more complex case.
The >>> symbol indicates that the concept definition represents a subtype of the concept.
This means that each instance of the definition is sufficient to represent a subtype of the concept 8801005 |Secondary diabetes mellitus (disorder)| .
The definition does not represent a necessary condition, i.e. the definition is not necessarily true for all instances of the concept 8801005 |Secondary diabetes mellitus (disorder)| . Or, said in other words, not all cases of 8801005 |Secondary diabetes mellitus (disorder)| are caused by a medicinal product or a disease.
Possible stated view of the definition of |Secondary diabetes mellitus|
Sufficiently Defined
A sufficiently defined concept is a concept with one or more sufficient definitions.
Notes
A SNOMED CT concept is expressed in a human-readable form by its fully specified name (FSN).
A sufficiently defined concept has at least one sufficient definition that distinguishes it from any concepts or expressions that are neither equivalent to, nor subtypes of, the defined concept.
Examples
The concept 74400008 |appendicitis (disorder)| is sufficiently defined by the following definition because any concept for which these defining relationships are true, is either the disorder appendicitis or a subtype of appendicitis.
74400008 |appendicitis (disorder)| === 18526009 |disorder of appendix| : 116676008 |associated morphology| = 23583003 |inflammation| , 363698007 |finding site| = 66754008 |appendix structure|
If a concept has a sufficient definition, it is possible to infer whether another concept or a postcoordinated expression is a subtype of, or equivalent to, that concept.
Primitive
A primitive concept is a concept without a sufficient definition in the necessary normal form distributed in the relationship.
Notes
The meaning of a SNOMED CT concept is expressed in a human-readable form by its fully specified name. Each concept also has a formal concept definition that provides a computer-processable representation of the meaning of the concept.
A primitive concept has a concept definition that is not sufficient to computably distinguish it from other concepts.
Example
The concept 5596004 |atypical appendicitis (disorder)| is primitive because the following definition is not sufficient to distinguish atypical appendicitis from any other type of appendicitis:
5596004 |atypical appendicitis (disorder)| <<< 116680003 |is a| = 74400008 |appendicitis| 116676008 |associated morphology| = 23583003 |inflammation| 363698007 |finding site| = 66754008 |appendix structure|
Necessary Conditions
All SNOMED CT defining relationships currently released are necessarily (always) true for the concept defined. Relationships that are necessarily true are also know as necessary conditions.
A necessary condition is defined as a characteristic that is always true of a concept.
Example
If you have a 71620000 |fracture of femur| , the morphological abnormality 72704001 |fracture| must be present. Therefore, 116676008 | morphology| = 72704001 |fracture| is a necessary condition of 71620000 |fracture of femur| .
Sufficient Sets of Conditions
In practice there can be several sufficient definitions for a concept. That is to say several different ways in which a concept could be sufficiently defined by different sets of defining relationships For example:
Gastric ulcer is defined as follows:
397825006 |gastric ulcer| === 116680003 |is a| = 64572001 |disease| { 116676008 |associated morphology| = 56208002 |ulcer| , 363698007 |finding site| = 69695003 |stomach structure| }
This is a sufficient definition because any 56208002 |ulcer| in a 69695003 |stomach structure| is by definition a 397825006 |gastric ulcer| . Based on this definition:
Any postcoordinated expression that specified a disease involving an 56208002 |ulcer| with 363698007 |finding site| = 69695003 |stomach structure| would be equivalent to or a subtype of 397825006 |gastric ulcer|
However, a query for all disorders involving 78653002 |gastric mucosa| would incorrectly exclude 397825006 |gastric ulcer| as the site is specified as 78653002 |gastric mucosa| which is more specific than 69695003 |stomach structure| . In reality there is another sufficient set defining relationships
397825006 |gastric ulcer| === 116680003 |is a| = 64572001 |disease| { 116676008 |associated morphology| = 56208002 |ulcer| , 363698007 |finding site| = 78653002 |gastric mucosa| }
but this is not currently represented in SNOMED CT. The reason for this is that currently the profile of description logic used by SNOMED CT does not support representation of multiple sufficient sets.
When multiple sufficient sets are supported, satisfying a single sufficient set enables an inference to be made that all necessary conditions must also be true. For example
The definition 363698007 |finding site| = 78653002 |gastric mucosa| is a necessary condition for 397825006 |gastric ulcer| :
This is true because all gastric ulcers necessarily involve the 78653002 |gastric mucosa|
The definition 116676008 |morphology| = 56208002 |ulcer| and 363698007 |finding site| = 69695003 |stomach structure| is a sufficient definition for 397825006 |gastric ulcer| :
This is true because any ulcer in a stomach structure is a 397825006 |gastric ulcer|
Therefore, an assertion that a person has an 56208002 |ulcer| with 363698007 |finding site| 69695003 |stomach| is sufficient to imply that they have a 397825006 |gastric ulcer| :
Since a gastric ulcer necessarily involves the 78653002 | gastric mucosa| it should be possible to deduce that a person with an "ulcer" with finding site 69695003 |stomach| has a disorder of with a site 78653002 |gastric mucosa|
However, as the current profile does not enable recognition of multiple sufficient sets, the general rule is to represent the most general sufficient set as this gives the greatest coverage for subsumption testing. This approach is taken because including more defining relationships, without distinguishing them from the sufficient set means some logically equivalent expressions will not compute as equivalent to or subsumed by the defined concept. This occurs in any cases where the expression does not include one of the attributes in the definition - even if it was not part of the logically sufficient set.
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