path: root/doc/rfc/rfc1384.txt

Network Working Group                                          P. Barker
Requests for Comments 1384                     University College London
                                                   S.E. Hardcastle-Kille
                                                        ISODE Consortium
                                                            January 1993


                 Naming Guidelines for Directory Pilots

Status of this Memo

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

Abstract

   Deployment of a Directory will benefit from following certain
   guidelines.  This document defines a number of naming guidelines.
   Alignment to these guidelines is recommended for directory pilots.

1  Introduction

   As a pre-requisite to this document, it is assumed that the COSINE
   and Internet X.500 Schema is followed [1].

2  DIT structure

   The majority of this document is concerned with DIT structure and
   naming for organisations, organisational units and personal entries.
   This section briefly notes three other key issues.

2.1  The top level of the DIT

   The following information will be present at the top level of the
   DIT:

   Participating Countries
      The entries should contain suitable values of the "Friendly
      Country" attribute.

   International Organisations
      An international organisation is an organisation, such as the
      United Nations, which inherently has a brief and scope covering
      many nations.  Such organisations might be considered to be
      supra-national and this, indeed, is the raison-d'etre of such
      organisations.  Such organisations will almost all be governmental
      or quasi-governmental.  A multi-national organisation is an



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      organisation which operates in more than one country, but is not
      supra-national.  This classification includes the large commercial
      organisations whose production and sales are spread throughout a
      large number of countries.

      International organisations, may be registered at the top level.
      This will not be done for multi-national organisations.  The only
      international organisation registered so far is:  Internet.  This
      is not a formal registration, but is adopted for the Internet
      Directory Service.

   Localities
      A few localities will be registered under the root.  The chief
      purpose of these locality entries is to provide a "natural" parent
      node for organisations which are supra-national, and yet which do
      not have global authority in their particular field.  Such
      organisations will usually be governmental or quasi-governmental.
      Example localities might include: Europe, Africa, West Indies.
      Example organisations within Europe might include: European Court
      of Justice, European Space Agency, European Commission.

   DSA Information
      Some information on DSAs may be needed at the top level.  This
      should be kept to a minimum.

   The only directory information for which there is a recognised top
   level registration authority is countries.  Registration of other
   information at the top level may potentially cause problems.  At this
   stage, it is argued that the benefits of additional top level
   registration outweighs these problems.  However, this potential
   problem should be noted by anyone making use of such a registration.

2.2  The DNS within the DIT

   The rules for the DNS parts of the DIT are defined in [3].  One
   modification to this is that the DNS tree will be rooted under
   "O=Internet", rather than at the root of the DIT.

2.3  Access control

   An entry's object class attribute, and any attribute(s) used for
   naming an entry are of special significance and may be considered to
   be "structural".  Any inability to access these attributes will often
   militate against successful querying of the Directory.  For example,
   user interfaces typically limit the scope of their searches by
   searching for entries of a particular type, where the type of entry
   is indicated by its object class.  Thus, unless the intention is to
   bar public access to an entry or set of entries, the object class and



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   naming attributes should be publicly readable.

3  Naming Style

   The first goal of naming is to provide unique identifiers for
   entries.  Once this is achieve, the next major goal in naming entries
   should be to facilitate querying of the Directory.  In particular,
   support for a naming structure which facilitates use of user friendly
   naming is desirable.  Other considerations, such as accurately
   reflecting the organisational structure of an organisation, should be
   disregarded if this has an adverse effect on normal querying.  Early
   experience in the pilot has shown that a consistent approach to
   structure and naming is an aid to querying using a wide range of user
   interfaces, as interfaces are often optimised for DIT structures
   which appear prevalent.

   Naming is dependent on a number of factors and these are now
   considered in turn.

3.1  National Guidelines

   Where naming is being done in a country which has established
   guidelines for naming, these guidelines should in general be
   followed.  These guidelines might be based on an established
   registration authority, or may make use use of an existing
   registration mechanism (e.g., company name registration).

   Where an organisation has a name which is nationally registered in an
   existing registry, this name is likely to be appropriate for use in
   the Directory, even in cases where there are no national guidelines.

3.2  Structure Rules

   A DIT structure is suggested in Annex B of X.521, and it is
   recommended that Directory Pilots should follow a slightly modified
   form of these guidelines.  The rules should be extended for handling
   DNS [3].  Some simple restrictions should be applied, as described
   below.

   For most countries pilots, the following simple structure should
   suffice.  The country entry will appear immediately beneath the root
   of the tree.  Organisations which have national significance should
   have entries immediately beneath their respective country entries.
   Smaller organisations which are only known in a particular locality
   should be placed underneath locality entries representing states or
   similar geographical divisions.  Large organisations will probably
   need to be sub-divided by organisational units to help in the
   disambiguation of entries for people with common names.  Entries for



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   people and roles will be stored beneath organisations or
   organisational units.  An example plan evolving for the US is the
   work of the North American Directory Forum [2].

   As noted above, there will be a few exceptions to this basic
   structure.  International organisations will be stored immediately
   under the root of the tree.  Multi-national organisations will be
   stored within the framework outlined, but with some use of aliases
   and attributes such as seeAlso to help bind together the constituent
   parts of these organisations.  This is discussed in more detail
   later.

3.3  Depth of tree

   The broad recommendation is that the DIT should be as flat as
   possible.  A flat tree means that Directory names will be relatively
   short, and probably somewhat similar in length and component
   structure to paper mail addresses.  A deep DIT would imply long
   Directory names, with somewhat arbitrary component parts, with a
   result which it is argued seems less natural.  Any artificiality in
   the choice of names militates against successful querying.

   A presumption behind this style of naming is that most querying will
   be supported by the user specifying convenient strings of characters
   which will be mapped onto powerful search operations.  The
   alternative approach of the user browsing their way down the tree and
   selecting names from large numbers of possibilities may be more
   appropriate in some cases, and a deeper tree facilitates this.
   However, these guidelines recommend a shallow tree, and implicitly a
   search oriented approach.

   It may be considered that there are two determinants of DIT depth:
   first, how far down the DIT an organisation is placed; second, the
   structure of the DIT within organisations.

   The structure of the upper levels of the tree will be determined in
   due course by various registration authorities, and the pilot will
   have to work within the given structure.  However, it is important
   that the various pilots are cognisant of what the structures are
   likely to be, and move early to adopt these structures.

   The other principal determinant of DIT depth is whether an
   organisation splits its entries over a number of organisational
   units, and if so, the number of levels.  The recommendation here is
   that this sub-division of organisations is kept to a minimum.  A
   maximum of two levels of organisational unit should suffice even for
   large organisations.  Organisations with only a few tens or hundreds
   of employees should strongly consider not using organisational units



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   at all.  It is noted that there may be some problems with choice of
   unique RDNs when using a flat DIT structure.  Multiple value RDNs can
   alleviate this problem.  The standard recommends that an
   organizationalUnitName attribute can also be used as a naming
   attribute to disambiguate entries.  Further disambiguation may be
   achieved by the use of a personalTitle attribute in the RDN.

3.4  Organisation and Organisational Unit Names

   The naming of organisations in the Directory will ultimately come
   under the jurisdiction of official naming authorities.  In the
   interim, it is recommended that pilots and organisations follow these
   guidelines.  An organisation's RDN should usually be the full name of
   the organisation, rather than just a set of initials.  This means
   that University College London should be preferred over UCL. An
   example of the problems which a short name might cause is given by
   the proposed registration of AA for the Automobile Association.  This
   seems reasonable at first glance, as the Automobile Association is
   well known by this acronym.  However, it seems less reasonable in a
   broader perspective when you consider organisations such as
   Alcoholics Anonymous and American Airlines which use the same
   acronym.  Just as initials should usually be avoided for
   organisational RDNs, so should formal names which, for example, exist
   only on official charters and are not generally well known.  There
   are two reasons for this approach:

   1.  The names should be meaningful.

   2.  The names should uniquely identify the organisation, and be a
       name which is unlikely to be challenged in an open registration
       process.  For example, UCL might well be challenged by United
       Carriers Ltd.

   The same arguments on naming style can be applied with even greater
   force to the choice of RDNs for organisational units.  While
   abbreviated names will be in common parlance within an organisation,
   they will almost always be meaningless outside of that organisation.
   While many people in academic computing habitually refer to CS when
   thinking of Computer Science, CS may be given several different
   interpretations.  It could equally be interpreted as Computing
   Services, Cognitive Science, Clinical Science or even Counselling
   Services.

   For both organisations and organisational units, extra naming
   information should be stored in the directory as alternative values
   of the naming attribute.  Thus, for University College London, UCL
   should be stored as an alternative organizationName attribute value.
   Similarly CS could be stored as an alternative organizationalUnitName



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   value for Computer Science and any of the other departments cited
   earlier.  In general, entries will be located by searching, and so it
   is not essential to have names which are either memorable or
   guessable.  Minimising of typing may be achieved by use of carefully
   selected alternate values.

3.5  Naming human users

   A reasonably consistent approach to naming people is particularly
   critical as a large percentage of directory usage will be looking up
   information about people.  User interfaces will be better able to
   assist users if entries have names conforming to a common format, or
   small group of formats.  It is suggested that the RDN should follow
   such a format.  Alternative values of the common name attribute
   should be used to store extra naming information.  It seems sensible
   to try to ensure that the RDN commonName value is genuinely the most
   common name for a person as it is likely that user interfaces may
   choose to place greater weight on matches on the RDN than on matches
   on one of the alternative names.  It is proposed that pilots should
   ignore the standard's recommendations on storing personal titles, and
   letters indicating academic and professional qualifications within
   the commonName attribute, as this overloads the commonName attribute.
   A personalTitle attribute has already been specified in the COSINE
   and Internet Schema, and another attribute could be specified for
   information about qualifications.

   Furthermore, the common name attribute should not be used to hold
   other attribute information such as telephone numbers, room numbers,
   or local codes.  Such information should be stored within the
   appropriate attributes as defined in the COSINE and Internet X.500
   Schema.  If such attributes have to be used to disambiguate entries,
   multi-valued RDNs should be used, such that other attribute(s) be
   used for naming in addition to a common name.

   The choice of RDN for humans will be influenced by cultural
   considerations.  In many countries the best choice will be of the
   form familiar-first-name surname.  Thus, Steve Hardcastle-Kille is
   preferred as the RDN choice for one of this document's co-authors,
   while Stephen E. Hardcastle-Kille is stored as an alternative
   commonName value.  Sets of initials should not be concatenated into a
   single "word", but be separated by spaces and/or "." characters.
   Pragmatic choices will have to be made for other cultures.

3.6  Application Entities

   The guidelines of X.521 should be followed, in that the application
   entity should always be named relative to an Organisation or
   Organisational Unit.  The application process will often correspond



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   to a system or host.  In this case, the application entities should
   be named by Common Names which identify the service (e.g., "FTAM
   Service").  In cases where there is no useful distinction between
   application process and application entity, the application process
   may be omitted (This is often done for DSAs in the current pilot).

4  Multinational Organisations

   The standard says that only international organisations may be placed
   under the root of the DIT. This implies that multi-national
   organisations must be represented as a number of separate entries
   underneath country or locality entries.  This structure makes it more
   awkward to use X.500 within a multi-national to provide an internal
   organisational directory, as the data is now spread widely throughout
   the DIT, rather than all being grouped within a single sub-tree.
   Many people have expressed the view that this restriction is a severe
   limitation of X.500, and argue that the intentions of the standard
   should be ignored in this respect.  This note argues, though, that
   the standard should be followed.

   No attempt to precisely define multinational organisation is essayed
   here.  Instead, the observation is made that the term is applied to a
   variety of organisational structures, where an organisation operates
   in more than one country.  This suggests that a variety of DIT
   structures may be appropriate to accommodate these different
   organisational structures.  This document suggests three approaches,
   and notes some of the characteristics associated with each of these
   approaches.

   Before considering the approaches, it is worth bearing in mind again
   that a major aim in the choice of a DIT structure is to facilitate
   querying, and that approaches which militate against this should be
   avoided wherever possible.


















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4.1  The multi-national as a single entity


                             ROOT
                           /  |  \
                          /   |   \
                       C=GB  C=FR  C=US
                      /       |        \
                     /        |         \
           O=MultiNat---->O=MultiNat<----O=MultiNat
                          /    |   \
                         /     |    \
                        /      |     \
                   l=abc    ou=def    l=fgi


---> means "alias to"

           Figure 1:  The multi-national as a single entity


   In many cases, a multi-national organisation will operate with a
   highly centralised structure.  While the organisation may have large
   operations in a number of countries, the organisation is strongly
   controlled from the centre and the disparate parts of the
   organisation exist only as limbs of the main organisation.  In such a
   situation, the model shown in figure 1 may be the best choice.  The
   organisation's entries all exist under a single sub-tree.  The
   organisational structure beneath the organisation entry should
   reflect the perceived structure of the organisation, and so no
   recommendations on this matter can be made here.  To assist the
   person querying the directory, alias entries should be created for
   all countries where the organisation operates.

4.2  The multi-national as a loose confederation

   Another common model of organisational structure is that where a
   multi-national consists of a number of national entities, which are
   in large part independent of both sibling national entities, and of
   any central entity.  In such cases, the model shown in Figure 2 may
   be a










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                             ROOT
                           /  |  \
                          /   |   \
                       C=GB  C=FR  C=US
                      /       |        \
                     /        |         \
           O=MultiNat     O=MultiNat     O=MultiNat
          /    |          /    |   \          |    \
         /     |         /     |    \         |     \
       L=GB   L=FR      /      |     \       L=FR   L=US
                      L=GB    L=FR  L=US


---> means "alias to"


        Figure 2:  The multi-national as a loose confederation


   better choice.  Organisational entries exist within each country, and
   only that country's localities and organisational units appear
   directly beneath the appropriate organisational entry.  Some binding
   together of the various parts of the organisation can be achieved by
   the use of aliases for localities and organisational units, and this
   can be done in a highly flexible fashion.  In some cases, the
   national view might not contain all branches of the company, as
   illustrated in Figure 2.

4.3  Loosely linked DIT sub-trees


   A third approach is to avoid aliasing altogether, and to use the
   looser binding provided by an attribute such as seeAlso.  This
   approach treats all parts of an organisation as essentially separate.

   A unified view of the organisation can only be achieved by user
   interfaces choosing to follow the seeAlso links.  This is a key
   difference with aliasing, where decisions to follow links may be
   specified within the protocol.  (Note that it may be better to
   specify another attribute for this purpose, as seeAlso is likely to
   be used for a wide variety of purposes.)

4.4  Summary of advantages and disadvantages of the above approaches

   Providing an internal directory
      All the above methods can be used to provide an internal
      directory.  In the first two cases, the linkage to other parts of
      the organisation can be followed by the protocol and thus



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      organisation-wide searches can be achieved by single X.500
      operations.  In the last case, interfaces would have to "know" to
      follow the soft links indicated by the seeAlso attribute.

   Impact on naming
      In the single-entity model, all DNs within the organisation will
      be under one country.  It could be argued that this will often
      result in rather "unnatural" naming.  In the loose-confederation
      model, DNs are more natural, although the need to disambiguate
      between organisational units and localities on an international,
      rather than just a national, basis may have some impact on the
      choice of names.  For example, it may be necessary to add in an
      extra level of organisational unit or locality information.  In
      the loosely-linked model, there is no impact on naming at all.

   Views of the organisation
      The first method provides a unique view of the organisation.  The
      loose confederacy allows for a variety of views of the
      organisation.  The view from the centre of the organisation may
      well be that all constituent organisations should be seen as part
      of the main organisation, whereas other parts of the organisation
      may only be interested in the organisation's centre and a few of
      its sibling organisations.  The third model gives an equally
      flexible view of organisational structures.

   Lookup performance
      All methods should perform reasonably well, providing information
      is held, or at least replicated, within a single DSA.

5  Miscellany

   This section draws attention to two areas which frequently provoke
   questions, and where it is felt that a consistent approach will be
   useful.

5.1  Schema consistency of aliases

   According to the letter of the standard, an alias may point at any
   entry.  It is beneficial for aliases to be ``schema consistent''.
   The following two checks should be made:

   1.  The Relative Distinguished Name of the alias should be a valid
       Relative Distinguished Name of the entry.

   2.  If the entry (aliased object) were placed where the alias is,
       there should be no schema violation.





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5.2  Organisational Units

   There is a problem that many organisations can be either
   organisations or organisational units, dependent on the location in
   the DIT (with aliases giving the alternate names).  For example, an
   organisation may be an independent national organisation and also an
   organisational unit of a parent organisation.  To achieve this, it is
   important to allow an entry to be of both object class organisation
   and of object class organisational unit.

References

   [1] P. Barker and S.E. Hardcastle-Kille. The COSINE and Internet
       X.500 schema. Request for Comments RFC 1274, Department of
       Computer Science, University College London, November 1991.

   [2] The North American Directory Forum.  A Naming Scheme for C=US,
       September 1991. Also NADF-175.

   [3] S.E. Hardcastle-Kille. X.500 and domains.  Request for Comments
       RFC 1279, Department of Computer Science, University College
       London, November 1991.

6  Security Considerations

   Security issues are not discussed in this memo.

























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7  Authors' Addresses

       Paul Barker
       Department of Computer Science
       University College London
       Gower Street
       WC1E 6BT
       England

       Phone:+44-71-380-7366


       EMail:  P.Barker@CS.UCL.AC.UK

       Steve Hardcastle-Kille
       ISODE Consortium
       P.O. Box 505
       London
       SW11 1DX
       England


       Phone:+44-71-223-4062


       EMail:  S.Kille@ISODE.COM

























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