Definitions for talking about directories
RFC 3254

Document Type RFC - Informational (April 2002; No errata)
Author Harald Alvestrand 
Last updated 2013-03-02
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Network Working Group                                      H. Alvestrand
Request for Comments: 3254                                 Cisco Systems
Category: Informational                                       April 2002

               Definitions for talking about directories

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.


   When discussing systems for making information accessible through the
   Internet in standardized ways, it may be useful if the people who are
   discussing it have a common understanding of the terms they use.

   For example, a reference to this document would give one the power to
   agree that the DNS (Domain Name System) is a global lookup repository
   with perimeter integrity and loose, converging consistency.  On the
   other hand, a LDAP (Lightweight Directory Access Protocol) directory
   server is a local, centralized repository with both lookup and search

   This document discusses one group of such systems which is known
   under the term, "directories".

1. Introduction and basic terms

   We suggest using the following terms for the remainder of this

   -  Information: Facts and ideas which can be represented (encoded) as
      data in various forms.

   -  Data: Information in a specific physical representation, usually a
      sequence of symbols that have meaning; especially a representation
      of information that can be processed or produced by a computer.
      (From [SEC].)

   -  Repository: An amount of data that is accessible through one or
      more access methods.

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RFC 3254       Definitions for talking about directories      April 2002

   -  Requester: Entity that may (try to) access data in a repository.
      Note that no assumption is made that the requester is animal,
      vegetable, or mineral.

   -  Maintainer: Entity that causes changes to the data in the
      repository. Usually, all maintainers are requesters, since they
      need to look at the data too, however, the roles are distinct.

   -  Access method: Well-defined series of operations that will cause
      data available from a repository to be obtained by the requester.

   -  Site: Entity that hosts all or part of a repository, and makes it
      available through one or more access methods.  A site may in
      various contexts be a machine, a datacenter, a network of
      datacenters, or a single device.

   This document is not intended to be either comprehensive or
   definitive, but is intended to give some aid in mutual comprehension
   when discussing information access methods to be incorporated into
   Internet Standards-Track documents.

2. Dimensions of classification

2.1 Uniqueness and scope

   Some information systems are global, in the sense that only one can
   sensibly exist in the world.

   Others are inherently local, in that each locality, site or even box
   will run its own information store, independent of all others.

   The following terms are suggested:

   -  Global repository: A repository that there can be only one of in
      the world.  The world itself is a prime example; the public
      telephone system's number assignments according to E.164 is

   -  Local repository: A class of repository of which multiple
      instances can exist, each with information relevant to that
      particular repository, with no need for coordination between them.

   -  Centralized repository: A repository where all access to data has
      to pass through some single site.

   -  Distributed repository: A repository that is not centralized; that
      is, access to data can occur through multiple sites.

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RFC 3254       Definitions for talking about directories      April 2002

   -  Replicated repository: A distributed repository where all sites
      have the same information.

   -  Cooperative repository: A distributed repository where not all
      sites have all the information, but where mechanisms exist to get
      the info to the requester, even when it is not available to the
      site originally asked.

   Note: The term "global" is often a matter of social or legal context;
   for instance, the E.164 telephone numbering system is global by
   international treaty, while the debate about whether the Domain Name
   System is global in fact or just a local repository with ambitions
   has proved bait for too many discussions to enumerate.

   Some claim that globality is in the eye of the beholder; "everything
   is local to some context".  When discussing technology, it may be
   wise to use "very widely deployed" instead.
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