This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.
The Concept Model is used to specify logical definitions of SNOMED CT concepts. It is based on a combination of formal logic and editorial rules and includes the attributes and values that may be applied to concepts.
The set of rules that determines the permitted sets of relationships between particular types of concepts
The Concept Model specifies the attributes that can be applied to concepts in particular domains and the ranges of permitted values for each of these attributes. There are also additional rules on the cardinality and grouping of particular types of relationships
This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.
Defining characteristics represent the values of a range of relevant attributes. Depending on the nature of the concept, they may include etiology, topography, method, etc.
The attributes that can be applied depend on the domain of the concept. For example, a procedure may have a method, and a disorder may have an etiology, but a procedure cannot have an etiology, and disorder cannot have a method. Defining characteristics using a particular attribute will be applied consistently to all concepts to which it is relevant. Note that this design principle may not be fully realized for all attributes in each release.
Defining characteristics are represented as relationships. The fields are used as follows:
SourceId refers to the concept to which a defining characteristic applies;
TypeId indicates the nature of the defining attribute;
DestinationId refers to the concept that represents the value of that attribute.
The defining characteristics can be divided into 116680003 | Is a (attribute)| relationships and defining attribute relationships.
The IS_A relationship (also called supertype-subtype or parent-child relationship) builds the hierarchies in SNOMED CT. Every concept has at least one IS_A relationship to a supertype or parent concept except the top level concept, 138875005 | SNOMED CT Concept (SNOMED RT+CTV3)| .
Each concept in SNOMED CT is logically defined through its relationships to other concepts. A relationship is defined as an association between a source concept and a destination concept. The type of association is indicated by an attribute concept. It is the relationships that make up the defining characteristics of the concepts. A defining characteristic is a relationship to a target concept that is always necessarily true for any instance of the source concept.
For example, the defining relationships of the concept 53442002 |Excision of stomach structure (procedure)| include:
116680003 | Is a (attribute)| = 65801008 | Excision (procedure)|
260686004 | Method (attribute)| = 129304002 | Excision - action (qualifier value)|
405813007 | Procedure site - Direct (attribute)| = 69695003 | Stomach structure (body structure)|This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.
Represents a characteristic of the meaning of a concept or the nature of a refinement
An attribute has a name which is represented by a concept. All of the concepts that can be used to name attributes are subtypes of the concept 410662002
Concept model attribute (attribute)
Not all hierarchies in SNOMED CT have defining attributes. Many attributes apply to top-level domain hierarchies, some to more than one. Some attributes to a lower-level, or a more specific, domain hierarchy. Primitive concepts in some hierarchies may be attribute values in top-level hierarchies.
New attributes should include a text definition clearly indicating what the attribute means in the context of SNOMED CT.
Attributes should be named to clearly communicate the property they specify and should refer to only one distinct property. The meaning of the attribute should not change if new values are added to the range. If a new attribute is needed, look at existing unapproved SNOMED CT attributes and as well as other ontologies to see if a suitable attribute exists, including Basic Formal Ontology (BFO) (), Relations Ontology (RO) (), and Gene Ontology (GO) () as example ontologies to review.
Attributes should be named as verb senses, so that object-attribute-value relationships may actually be read. For example, a name of "Has filling (attribute)" is preferred over "Filling (attribute)" and "Has property (attribute)" is preferred over "Property (attribute)." Then a concept such as 464376000 |Saline-filled breast implant (physical object)| could be defined with the attribute "Has filling (attribute)" and a value of 387390002 |Sodium chloride (substance)|.
Many of the attributes in SNOMED CT have a range that includes SCTIDs as an allowed value. Attributes which have a binary (e.g., Boolean) value shall be valued using a descendant of 1119301001 |Boolean value (qualifier value)|: 31874001 |True (qualifier value)|; 64100000 |False (qualifier value)|. In the July 2021 release, a new attribute was created which uses Boolean style value: 1148965004 |Is sterile (attribute)|.
Selected SNOMED CT attributes have a hierarchical relationship to one another known as attribute hierarchies. In an attribute hierarchy, one general attribute is the parent of one or more specific subtypes of that attribute. Concepts defined using the more general attribute can inherit concepts modeled with the more specific subtypes of that attribute providing the attribute value is the same or a subtype of the attribute value used for the concept that is defined with the more general attribute.
Associated with
Causative agent
Due to
Temporally related to
Procedure Site
Procedure site - Direct
Procedure site - Indirect
Procedure device
All or part of
Proper part of
Constitutional part of
Regional part of
Has ingredient (not used in the international edition)
Has active ingredient
Has precise active ingredient
After
Before
During
Direct device
Indirect device
Using device
Using access device
Procedure morphology
Direct morphology
Indirect morphology
Lateral half of
Systemic part of
A constrained set of values that the Concept Model permits to be applied to a specific attribute when that attribute is applied to a concept in a particular domain
The range of permitted values that can be applied to an attribute is typically defined to include concepts in one or more branches of the subtype hierarchy.
The range for an attribute may include intensional or extensional definitions or both. An example of a range with an intensional definition is 370130000
Property (attribute)
This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.
A qualifying characteristic is expressed by an attribute-value pair. The attribute may have one value, from a range of values, based on the domain's concept model. If a particular qualifying characteristic is applied to a concept, the resulting expression represents a more tightly defined subtype of that concept.
For example,
It might be possible to qualify a disorder such as
53084003 | Bacterial pneumonia (disorder)| according to its clinical course (373933003 | Acute onset (qualifier value)| or 90734009 | Chronic (qualifier value)|) or severity (255604002 | Mild (qualifier value)|, 6736007 | Moderate (severity modifier) (qualifier value)|, or 24484000 | Severe (severity modifier) (qualifier value)|)
125605004 | Fracture of bone (disorder)| can be refined by qualifying it with 12611008 | Bone structure of tibia (body structure)| to represent the concept 31978002 | Fracture of tibia (disorder)|
This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.
A concept is defined as a clinical idea to which a unique concept identifier has been assigned. Concepts are associated with descriptions that contain human-readable terms describing the concept.
A term is defined as a human-readable phrase that names or describes a concept. A term is one of the properties of a description. Other properties of a description link the term to an identified concept and indicate the type of description, e.g. Fully Specified Name, Preferred Term, Synonym.
Concepts are linked to their more general parent concepts directly above them in a hierarchy. More general meanings, are usually at the top of the hierarchy. Descending levels of the hierarchy contain more specific or specialized meanings.
Concepts are logically defined by their relationships to each other.
In SNOMED CT, the default meaning of a concept is defined above. However, a concept may have other meanings in SNOMED CT, such as an:
Abbreviated name for the concept identifier. For clarity, this is should be referred to as an identifier(ID), code, or concept identifier (ID).
Idea or class of real-world entities (common usage meaning). For clarity, this is should be referred to as a clinical idea , clinical meaning, or code meaning.
The concept file includes a special concept referred to as the root concep t. It is the single concept that is at the top of the SNOMED CT concept hierarchy. All other concepts are descended from this root concept via at least one series of relationships of the Relationship type 116680003 | Is a (attribute)| , i.e. all other concepts are regarded as subclasses of this concept. The root concept code is . All other SNOMED CT concepts are subtypes of the root concept. Unlike other SNOMED CT concepts, the root concept is not a subtype of any other concept.
Concepts that are directly related to the root concept by a single relationship of the Relationship type 116680003 | Is a (attribute)| are referred to as top-level concepts. All other concepts are descended from at least one top-level concept via at least one series of relationships of the Relationship type 116680003 | Is a (attribute)| , i.e. all other concepts represent subclasses of the meaning of at least one top-level concept.
A concept that is directly related to the root metadata concept, 900000000000441003 | SNOMED CT Model Component (metadata)| by a single relationship of the relationship type IS_A. All metadata concepts are descended from at least one top-level metadata concept via at least one series of relationships with Relationship type IS_A. Metadata codes represent structural information about the terminology itself. The top-level metadata concepts represent broad groups of metadata.
Subtype relationships provide the main semantic hierarchy that relates concepts to one another. All active concepts, except the root concept, have subtype relationships with one or more concept. Each of these relationships indicate that a concept is a subtype of another concept.
Subtype relationships are expressed in the same way as other SNOMED CT relationships. They are identifiable by their fully specified names, e.g 116680003 |Is a (attribute)|.
For example,
53084003 |Bacterial pneumonia (disorder)| is a subtype of 233604007 |Pneumonia (disorder)| because it is a subtype of 312342009 |Infective pneumonia (disorder)| which is also a subtype of 233604007 |Pneumonia (disorder)|