> 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/implementation-guides/drug-model-implementation-guide/content-development/drug-extension-development-principles/content-representation.md).
# Content Representation
## SNOMED CT Extension Format β Drug Content in RF2
### Overview
SNOMED CT drug content, whether part of the International Edition or a national drug extension, is distributed using Release Format 2 (RF2). RF2 provides a structured, tabular representation of terminology components, enabling consistent storage, exchange, and processing of SNOMED CT data.
In RF2, a medicinal product is not represented as a single record, but as a set of coordinated entries across multiple files:
* the Concept file identifies the drug concept
* the Description file provides human-readable names
* the Relationship file defines the meaning of the drug
* Reference sets (refsets) provide additional context such as language preferences and mappings
Each row in these files represents a single component, and together they form a computable definition of a medicinal product.
### Example Scenario: Representing a Real Drug
Consider the following real-world product:
> Brand X amoxicillin 500 mg oral capsule (real clinical drug)
In RF2, this product is reconstructed from multiple components across files.
### Concept File β Identifying the Drug
The Concept file contains one row per concept. For a drug, this row represents the existence of the medicinal product.
```
id effectiveTime active moduleId definitionStatusId
999001234 20250131 1 EXT_MODULE Fully defined
```
In drug context:
* This row represents the Real Clinical Drug (RCD) concept
* The concept itself has no meaning without descriptions and relationships
* It acts as the anchor identifier for all related information
{% hint style="info" %}
π Think of this as: *βThis drug exists in the terminology.β*
{% endhint %}
### Description File β Naming the Drug
The Description file provides the human-readable terms associated with the concept.
```
id conceptId typeId term
888001 999001234 FSN Brand X amoxicillin 500 mg oral capsule (real clinical drug)
888002 999001234 Synonym Brand X amoxicillin 500 mg capsule
```
In drug context:
* The Fully Specified Name (FSN) provides a precise and unambiguous description of the medicinal product
* Synonyms provide alternative terms used in prescribing, dispensing, and user interfaces
The acceptability of synonyms (e.g. which term is *preferred* for display) is not defined in the Description file itself. Instead, it is specified in a Language Reference Set, which indicates:
* which synonym is the preferred term
* which synonyms are acceptable alternatives
{% hint style="info" %}
π This allows different countries or systems to use different preferred terms for the same drug concept, while maintaining a shared underlying identifier and meaning.
{% endhint %}
### Relationship File β Defining the Drug
The Relationship file represent the defining properties (the definition) of the drug using structured relationships.
Each row represents a single relationship between concepts.
#### Clinical Definition (Inherited from International Model)
```
sourceId typeId destinationId
999001234 Has active ingredient Amoxicillin
999001234 Has dose form Oral capsule
999001234 Has strength 500 mg
```
In drug context:
These relationships define the clinical meaning of the drug:
* what substance it contains
* how it is administered
* how strong it is
{% hint style="info" %}
π This corresponds to the Clinical Drug (CD) definition.
{% endhint %}
#### Product Identity (Extension-Specific)
```
sourceId typeId destinationId
999001234 Has product name Brand X
999001234 Has manufacturer Company Y
```
In drug context:
These relationships distinguish this concept as a Real Clinical Drug (RCD):
* same clinical definition as other amoxicillin 500 mg capsules
* but a specific branded and authorized product
{% hint style="info" %}
π This is what makes it usable in dispensing and traceability.
{% endhint %}
### Packaging Example β Moving to RPCD
Now consider:
> BrandX amoxicillin 500 mg oral capsule box of 24 (real clinical drug package)
This concept includes additional packaging relationships:
```
sourceId typeId destinationId
999009999 Has pack size 24
999009999 Has unit of presentation Capsule
999009999 Is a Real clinical drug package
```
In drug context:
* These relationships describe how the product is packaged and supplied
* Combined with product identity, this forms a Real Clinical Drug Package (RPCD)
{% hint style="info" %}
π This level is used in inventory, logistics, and dispensing systems.
{% endhint %}
## Mapping to Local Drug Dictionaries
In addition to SNOMED CT content, extensions often include mapping artifacts that link SNOMED CT concepts to local drug dictionary identifiers.
These mappings support:
* interoperability between systems
* migration from legacy terminologies
* integration with national regulatory and reimbursement systems
### Reference Sets β Adding Context
Reference sets provide additional, non-defining information.
#### Example: Mapping to a National Drug Code
```
referencedComponentId mapTarget
999001234 AMOX500_BRANDX
```
In drug context:
* Links the SNOMED CT concept to a local drug dictionary or regulatory identifier
* Supports integration with pharmacy, billing, and regulatory systems
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