# Defining Characteristics

<mark style="color:$danger;">**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.**</mark>

## Role of defining characteristics

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.

## Representation of defining characteristics

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.

## Relationships

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:

{% code title="53442002 |Excision of stomach structure (procedure)|" overflow="wrap" %}

```
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)|
```

{% endcode %}

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