This arc is for Directory Services.
This arc is the starting point for the Rec. ITU-T X.500 | ISO/IEC 9594 series.
Information:
The Directory is an international and distributed database that can store any kind of information about persons, organizations, communicating application entities, terminals, mailing lists, etc.
The Rec. ITU-T X.500 series can be downloaded from: http://www.itu.int/itudoc/itu-t/rec/x/x500up/
Hoyt Kesterson (Oct. 23, 2002): the only thing I think we use in the X.500 Series out of the joint arc is: ds ID ::= {joint-iso-itu-t ds(5)}
and all the OIDs defined in our standard are rooted there.