[the X. 500 directory is] a collection of open systems which co-operate to hold a logical data base of information about the set of objects in the real world. The users of the Directory, including people and computer programs, can read or modify the information, or parts of it, subject to having permission to do so.Trinity points out that the CCITT named the Directory in the singular to reflect the fact that it constitutes a single logical directory. Basically, X.500 defines: 1) the structure, model, and addressing syntax of the directory; 2) a set of Directory services to it's users; and 3) the Directory protocols. X.500 does not define the user interfaces nor does it define the implementation technology. In practical terms, X.500 offers access to a distributed, open, online directory. Thus, while the initial drive for X.500 is to provide directory support for the X.400 message handling systems (MHS) services, it also offers an open standard for a generalized directory capability, including support for: Open Systems Interconnection (OSI) File Transfer, Access and Management (FTAM) protocol, electronic data interchange (EDI), and network or international directory service; general White and Yellow Pages for a corporate directory or a national or international directory service, especially in telephony; and other business applications such as directories for inventories and authentication services.
While the X.500 directory is similar in many ways to a general purpose database management system, it is not designed to be one. However, the X.500 directory may be built on top of a general-purpose database system. Although the X.500 standard is best known for it's aim to provide universal directory services for business-quality E-mail, as envisioned in the M.U.S.E. report (1993) and by the General Services Administration (GSA) for implementation by the Federal Government, the scope is even broader than suggested by Trinity. For U.S. Federal implementation, the X.500 directory would be comprised of four segments:
If the M.U.S.E. directory is going to help people find Federal offices according to their mission/program activities [i.e., the Blue Pages], why should those people have to go somewhere else to find Federal information? ... Almost everyone who has been exposed to the educational process in the United States has learned to use a library catalog. In it, the library holdings are listed three different ways: by author, by title, and by subject. The catalog is a simple listing that almost everyone can understand and use. It is an obvious model for the Green Pages ...More recently, the X.500 plan (Booz, Allen & Hamilton, 1996) issued by GSA stated:
The Green Pages directory service provides a lookup facility for accessing bibliographic retrieval information. The purpose of the Green Pages directory is to provide directory users with retrieval information sufficient to enable them to identify an electronic document, determine the retrieval requirements, and retrieve it through an automated tool. The directory will support the ANSI Z39.50-to-X.500 Gateway protocol and the Government Information Locator Service (GILS) for integrated access to online Government document repositories.The schema for the X.500 directory is set forth in Appendix D of the X.500 Detailed Design document (Booz, Allen and Hamilton, p. 1-12). It comprises more than a hundred object classes, with attributes ranging from one to dozens per class. Among the object classes are two called "Document" and "Document Series". Seven attributes are specified for the Document Series object class:
A list of X.500 implementors and their implementations can be found on Internic's Web site (Internic). With respect to the focus of the X.500 directory on E-mail, in many cases E-mail is merely an inefficient way to find the information (documentation, i.e., "documents") that people need. In many cases, what is needed is not more E-mail. Instead, the exchange of fewer "messages" should be required in order to locate, retrieve, and share needed information.
The same is true of telephone calls and voice mail. In many cases, callers don't really need to talk with anyone, nor can organizations afford anymore to have people answering the phones. Often, callers just want information that already is or should already be documented. The Green Pages should help to cut down on needless E-mail and voice mail. The same is also true of Web pages. However, until the information served on the Web and/or via the Green Pages is comprehensive, people will still feel the need to call and send E-mail to find what may be missing. And that is why the new requirements of the E-FOIA are so important. If Federal agencies make available by electronic means all of their information holdings that are of significant public interest, as required by E-FOIA, they will be in a position to simply point callers and E-mailers to such information via the Web, Z39.50, and/or Green Pages indices. Then E-mail and telephone communications among people can focus on the higher-value function of identifying additional information needs, rather than simply chasing each other around to find information that has already been documented but which is inaccessible.
Booz, Allen & Hamilton, [X.500 planning document, title unknown],Center for Electronic Messaging, General Services Administration, July 30, 1996, pp. 4-3 and 4-4. Available at:
Booz, Allen & Hamilton, Detailed Design For A Government Electronic Directory, Center for Electronic Messaging, General Services Administration, July 30, 1996. Available at:
Boeyen. S. X.500 Services for Integrated Applications, Messaging Magazine, Bell-Northern Research. Available at:
Internic, List of X.500 Implementors and Implementations. Available at:
http://www.internic.net/projects/x500catalog/impselect.html[Back]Note: Apparently the list is no longer available. See
M.U.S.E. Report: A Unified Federal Government Electronic Mail Users' Support Environment, 1993. Available at:
Trinity College Dublin, Definition of X.500. Available at:
http://ganges.cs.tcd.ie/4ba2/x500/katie/x5model_p1.html[Back]Additional information available at: