It is important that extension producers understand how reference sets and their members are created. All extensions must include new members in the |Module dependency reference set| to define the modules on which the extension module(s) depend. Many extensions will also specify language or dialect preferences in a 900000000000506000|Language type reference set|. Some extensions may also include additional reference sets to extend the use of SNOMED CT. For example, a subset of concepts for use in a specific clinical setting can be distributed as a |Simple type reference set|.
The following subsections present the logical design rules and considerations for reference sets and reference set members in an extension: