X.500 is an international standard (OSI) for directory services, with a tree-like structure, the Directory Information Tree
(DIT). The X.500 system can be used to build a global directory database. Each of the X.500 servers contains a part of a global user database for this purpose and is networked with all other X.500 servers. From the user's point of view, access to the entire global X.500 database is thus possible at any time. The actual search process takes place on the respective X.500 servers (DSA), which can be accessed with X.500 clients.
The most widely used line-oriented X.500 client programs are Front End Directory (fred), Directory Enquiry (de) as a simple interface and Directory Shell (dish) as an interface with full X.500 functionality. X Window client programs include Xdi and Xlookup. On the public X.500 clients there are "wp.psi.com" (login:fred) and "nic.switch
.ch" (login: dua).DE, then only the four fields "name, department, organization, country" must be indicated for the information search. With the entry * all available entries are selected.