A set of ASN.1 source definitions that is compilable is termed an ASN.1 module. ASN.1 modules can be registered in the Map Library as a map. Modules are identified within the ASN.1 source, and this name must correspond to the registered map name. An ASN.1 module can also have a registered and unique identifier, called an object identifier, that officially identifies this module amongst all registered objects.
In general ASN.1 modules have a very free syntax, but Mapping Services imposes some restrictions on this for practical reasons.