> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-ct-specifications/snomed-ct-editorial-guide/readme/concept-model-overview/defining-characteristics.md).

# Defining Characteristics

## 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 %}

<a href="https://docs.google.com/forms/d/e/1FAIpQLScTmbZIf0UEQwYDkY27EEWBkaiYkHSbR0_9DmFrMLXoQLyL7Q/viewform?usp=pp_url&#x26;entry.1767247133=SCT+Editorial+Guide&#x26;entry.670899847=Defining%20Characteristics" class="button primary">Provide Feedback</a>


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://docs.snomed.org/snomed-ct-specifications/snomed-ct-editorial-guide/readme/concept-model-overview/defining-characteristics.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.