In some circumstances, the name mapper is asked to map a short name to the corresponding long name. The MLDAP ESM Module and the sample file-based mapping module can both do this, as long as the names they are configured to map are unique.
For short-to-long mapping, the default mapper simply returns the short name as the "long" name. This means that the default mapper does not reliably (one-to-one or isomorphically) map long names to short names and back again. For some system configurations this is not an issue; see Short-to-long Mapping for Verify for more information. If you wish to use long names for ordinary MSS users, as opposed to purely administrative use, you might want to use a name mapper other than the default one.