rfc1384
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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ERRATA
