RFC 3254 (rfc3254) - Page 3 of 11

Definitions for talking about directories

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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.

   Note: Locating the repositories changes with the scale of
   consideration.  For instance, the global DNS system is considered a
   distributed cooperative repository, built out of zone repositories
   that themselves may be distributed, and are always replicated when
   distributed.

2.2 Search, Lookup, Query and Notify

   A different consideration when describing repositories is the types
   of method they offer to find information.

   The chief classifications are:

   -  Lookup methods require the user to know or guess some exact value
      before asking for information, sometimes called a "lookup key" or
      "identifier" and sometimes called a "name".  The word "name" is
      NOT recommended, since it conflicts with other uses of that word
      The response to a successful lookup is a single group of
      information, often called "information about the identified
      entity". A lookup method is binary (yes/no) in recall: It either
      returns one result or no result; if it returns a result, that
      result is the right result for that lookup key, so it is also of
      binary precision (no info or completely relevant info).

   -  Search methods require the user to know some approximate value of
      some information.  They usually return zero, one, or more
      responses that match the information supplied according to some
      algorithm. Where the repository is structured around "entities",
      the information can be about zero, one, or many entities.




Alvestrand                   Informational
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