ADL has a small number of keywords which are reserved for use in archetype declarations, as follows:

All of these words can safely appear as identifiers in the definition and terminology sections.

Deprecated keywords include:

The first word in a source ADL archetype declares the artefact type, and is one of the following keywords:

The flattened form of any of the above types starts with the keyword 'flat' followed by the artefact type.

A fourth artefact type is also possible.

In the definition section of an ADL archetype, a specific set of codes is used as node identifiers. Identifier codes always appear in brackets ([] ), and begin with the 'id' prefix. Specialisations of locally coded concepts have the same root, followed by 'dot' extensions, e.g. [id10.2] . From a terminology point of view, these codes have no implied semantics - the 'dot' structuring is used as an optimisation on node identification.

In the definition section of an ADL archetype, a second set of codes is used for terms denoting constraints on coded items. Term codes are either local to the archetype, or from an external lexicon. This means that the archetype description is the same in all languages, and is available in any language that the codes have been translated to. All term codes are shown in brackets ([]) and are prefixed with "at", e.g. at10 . Codes of any length are acceptable in ADL archetypes. Specialisations of locally coded concepts have the same root, followed by 'dot' extensions, e.g. at10.2 . From a terminology point of view, these codes have no implied semantics - the 'dot' structuring is used as an optimisation on node identification.

A third kind of local code is used to stand for value set constraints on coded text items in the body of the archetype. Because they are language- and/or terminology-sensitive, they are defined in the terminology section, and referenced by codes prefixed by "ac", e.g. [ac9].