Network Working Group P. Barker
Request for Comments: 1617 University College London
RARE Technical Report: 11 S. Kille
Obsoletes: 1384 ISODE Consortium
Category: Informational T. Lenggenhager
May 1994 Naming and Structuring Guidelines for X.500 Directory Pilots
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Deployment of a Directory will benefit from following certain
guidelines. This document defines a number of naming and structuring
guidelines focused on White Pages usage. Alignment to these
guidelines is recommended for directory pilots. The final version of
this document will replace RFC 1384.
Table of Contents
1. Introduction 22. DIT Structure 32.1. Structure Rules 32.2. The Top Level of the DIT 32.3. Countries 42.4. Organisations 52.4.1. Directory Manager, Postmaster & Secretary 52.4.2. Depth of tree 62.4.3. Real World Organisational Structure 72.5. Multi-National Organisations 72.5.1. The Multi-National as a Single Entity 72.5.2. The Multi-National as a Loose Confederation 82.5.3. Loosely Linked DIT Sub-Trees 92.5.4. Summary of Advantages and Disadvantages of the
Above Approaches 93. Naming Style 103.1. Multi-Component Relative Distinguished Names 113.2. National Guidelines for Naming 113.3. Naming Organisation and Organisational Unit Names 113.4. Naming Human Users 123.5. Application Entities 13
4. Attribute Values 134.1. Basic Attribute Syntaxes 134.1.1. Printable String 144.1.2. IA5 String - T.50 144.1.3. Teletex String - T.61 144.1.4. Case Ignore String 144.1.5. Distinguished Name 144.2. Languages & Transliteration 144.2.1. Languages other than English 154.2.2. Transliteration 154.3. Access control 154.4. Selected Attributes 164.4.1. Personal Attributes 164.4.2. Organisational Attributes 184.4.3. Local Attributes 194.4.4. Miscellaneous Attributes 204.4.5. MHS Attributes 214.4.6. Postal Attributes 214.4.7. Telecom Attributes 225. Miscellany 225.1. Schema consistency of aliases 225.2. Organisational Units 236. References 237. Security Considerations 238. Authors' Addresses 249. Appendix - Example Entries 251. Introduction
The intended audience for this document are mainly data managers
using X.500 Directory Services. With the help of these guidelines it
should be easier for them to define the structure for the part of the
Directory Information Tree they want to model, e.g., the
representation of their organisation in the Directory. In addition,
decisions like which data elements to store for each kind of entry
shall be supported.
These guidelines concentrate mainly on the White Pages use of the
Directory, the X.500 application with most operational experience
today, nonetheless many recommendations are also valid for other
applications of the Directory.
As a pre-requisite to this document, it is assumed that the COSINE
and Internet X.500 Schema is followed .
2. DIT Structure
The majority of this document is concerned with DIT structure, naming
and the usage of attributes for organisations, organisational units
and personal entries.
This section briefly notes five other key issues.
2.1 Structure Rules
A DIT structure is suggested in Annex B of X.521 , and it is
recommended that Directory Pilots for White Pages services should
follow these guidelines. Some simple restrictions should be applied,
as described below. For further usage of the Directory like e-mail
routing with the Directory or storage of network information in the
Directory it will be necessary to follow the guidelines specified in
the respective documents.
One of the few exceptions to the basic DIT structure is, that
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 in section 2.5.
A general rule for the depth of a subtree is as follows: When a
subtree is mainly accessed via searching, it should be as flat as
possible to improve the performance, when the access will be mainly
through read operations, the depth of the subtree is not a
significant parameter for performance.
2.2 The Top Level of the DIT
The following information will be present at the top level of the
According to the standard the RDN is the ISO 3166 country code. In
addition, the entries should contain suitable values of the
friendlyCountryName attribute specified in RFC 1274. Use of this
attribute is described in more detail in section 4.4.4.
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
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. Currently
three organisations are registered so far: Inmarsat, Internet and
North Atlantic Treaty Organization.
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.
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 benefit of limiting additional top level
registrations outweighs these problems. However, this potential
problem should be noted by anyone making use of such a registration.
The national standardisation bodies will define national guidelines
for the structure of the national part of the DIT. In the interim,
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. Entry for private persons will be listed under the
locality entries. An example plan evolving for the US is the work of
the North American Directory Forum . Another example is the
organisation of the X.500 namespace as standardized in Australia .
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 people and roles will be stored
beneath organisations or organisational units.
The organisation entry itself shall contain the information necessary
to contact the organisation: for example, postal address, telephone
and fax numbers.
Although the structure of organisations often changes considerably
over time, the aim should be to minimise the number of changes to the
DIT. Note that renaming a superior, department entry has the effect
of changing the DN of all subordinate entries. This has an
undesirable impact on the service for several reasons. Alias entries
and certain attributes or ordinary entries such as seeAlso, secretary
and roleOccupant use DNs to maintain links with other entries. These
references are one-way only and the Directory standard offers no
support to automatically update all references to an entry once its
2.4.1 Directory Manager, Postmaster & Secretary
Similar to messaging, where every domain has its postmaster address
it is highly recommended that each organisation in the X.500
Directory has two entries: Postmaster and Directory Manager. In
addition, Secretary entries for an organisation and its units should
be listed. If this guidance is followed, users will benefit because
it will be straightforward to find the right contacts for questions
or problems with the service.
These entries should use the object class organizationalRole with the
roleOccupant attributes containing the distinguished names of the
persons in charge of this role. The values
should be added as additional values whenever another language than
English is used for the name of the entries.
2.4.2 Depth of tree
The broad recommendation for White Pages 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
at all. It is noted that there may be some problems with choice of
unique RDNs when using a flat DIT structure. Multi-component RDNs can
alleviate this problem: see section 3.1. The standard X.521
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 or
userId attribute in the RDN.
2.4.3 Real World Organisational Structure
Another aspect on designing the DIT structure for an organisation is
the administrative structure within a company. Using the same
structure in the DIT might help in distributing maintenance authority
to the different units. Please note comments on the stability of the
DIT structure in section 2.4.
2.5 Multi-National 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
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.
2.5.1 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.
/ | \
/ | \
C=GB C=FR C=US
/ | \
/ | \
/ | \
/ | \
/ | \
l=abc ou=def l=fgi
---> means "alias to"
Figure 1: The multi-national as a single entity
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 under all
countries where the organisation operates.
2.5.2 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 better choice. Organisational entries exist within each country,
and only that country's localities and organisational units appear
directly beneath the appropriate organisational entry.
/ | \
/ | \
C=GB C=FR C=US
/ | \
/ | \
O=MultiNat O=MultiNat O=MultiNat
/ | / | \ | \
/ | / | \ | \
L=FR L=GB<---L=GB | L=US--->L=US L=FR
\ | /
---> means "alias to"
Figure 2: The multi-national as a loose confederation
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.
2.5.3 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.)
2.5.4 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
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.
All methods should perform reasonably well, providing information
is either held within a single DSA or it is replicated to the
3. Naming Style
The first goal of naming is to provide unique identifiers for
entries. Once this is achieved, 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. In addition, the X.501 standard notes that
"RDNs are intended to be long-lived so that the users of the
Directory can store the distinguished names of objects..." and "It is
preferable that distinguished names of objects which humans have to
deal with be user-friendly." 
Naming is dependent on a number of factors and these are now
considered in turn.
3.1 Multi-Component Relative Distinguished Names
According to the standard, relative distinguished names may have more
than one component selected from the set of the attributes of the
entry to be named. This is useful when there are, for example, two
"John Smiths" in one department. The use of multi-component relative
distinguished names allows one to avoid artificial naming values such
as "John Smith 1" or "John Smith-2". Attributes which could be used
as the additional naming attribute include: personalTitle,
roomNumber, telephoneNumber, and userId.
3.2 National Guidelines for Naming
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 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.
3.3 Naming 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 that organisations such as
Alcoholics Anonymous and American Airlines 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
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
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
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 RDNs which are either the most memorable or
guessable, although names should be recognisable. The need for users
not to type long names may be achieved by use of carefully selected
3.4 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.
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 Kille is preferred as the
RDN choice for one of this document's co-authors, while Stephen E.
Kille is stored as an alternative commonName value. Pragmatic choices
will have to be made for other cultures. 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. Section 3.1 on multi-component RDNs
shows how clashing names can be made unique.
The choice of a naming strategy should not be made on the basis of
the possibilities of the currently available user interface
implementations. For example, it is inappropriate to use common names
of the form 'surname firstname' merely because a user interface
presents results in a more satisfactory order by so doing. Use the
best structure for human names, and fix the user interface!
More details on the use of commonName in section 4.4.1.
3.5 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 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. Attribute Values
In general the attribute values should be used as documented in the
standards. Sometimes the standard is not very precise about which
attribute to use and how to represent a value.
The following sections give recommendations how to use them in X.500
4.1 Basic Attribute Syntaxes
Every attribute type has a definition of the attribute syntaxes its
values may be use. Most attribute types make use the basic attribute
4.1.1 Printable String
This most simple syntax uses a subset of characters from ISO 646 IRV.
A-Z a-z 0-9 ' ( ) +
, - . / : ? space
Tab 1: Characters in PrintableString
4.1.2 IA5 String - T.50
The International Alphabet No. 5 (IA5) is known from the X.400
message handling service. It covers a wider range of characters than
the printable string. The international reference version of IA5
offers the same set of characters as ISO 646 IRV.
4.1.3 Teletex String - T.61
The Teletex character set is a very unusual one in the computing
environment because it uses mixed one and two octet character codes
which are more difficult to handle than single octet codes. Most of
the characters can be mapped to the more often supported 8-bit
character set standard ISO 8859-1 (ISO Latin-1).
4.1.4 Case Ignore String
Many attributes use this case insensitive syntax. It allows attribute
values to be represented using a mixture of upper and lower case
letters, as appropriate. Matching of attribute values, however, is
performed such that no significance is given to case.
4.1.5 Distinguished Name
A Distinguished Name should currently never contain a value in T.61
string syntax because most users would not be able to view or type it
correctly by lack of appropriate hardware/software configuration.
Therefore, only the characters defined in printable string syntax
should be used as part of a RDN. The correct representation of the
name should be added as additional attribute value to match for
4.2 Languages & Transliteration
The standard as available has no support at all for the use of
different languages in the Directory. It is e.g., not possible to add
a language qualifier to a description attribute nor is it possible to
use characters beyond the Teletex character set.
4.2.1 Languages other than English
Many countries have more than one national language and a world-wide
Directory must be able to support non-English-speaking users.
Until the standard provides a solution for this problem it is
possible to make use of multi-valued attributes to specify a value
not only in the local languages but also in English.
In particular the friendlyCountryName, stateOrProvinceName and
localityName attributes should use the most often used translations
of its original value to increase the chance for successful searches
also for users with a foreign language. Other attributes like
description, organizationName and organizationalUnitName attributes
should provide multi-lingual values where appropriate.
The drawback of this solution is, that the user interfaces present
much redundant information because they are not able to know the
language of the values and make an automatic selection.
Note: The sequence of multi-valued attribute values in an entry
cannot be defined. It is always up to the DSA to decide on
which order to store them and return them as results, and
to the DUA to decide on which order to display them.
What measures can be taken to make sure all users are able to read an
attribute, when a value uses one of the special characters from the
T.61 character set? An interim solution is transliteration as used in
earlier days with the typewriters, where e.g., the German 'a' with
umlaut is written as 'ae'. Transliteration is not necessarily unique
since it is dependent on the language, English speakers transliterate
the 'a' with umlaut just to an 'a'. However, it is an improvement
over just using the T.61 value since it may not be possible to
display such a value at all. Whenever an attribute needs a character
not in PrintableString and the attribute syntax allows the use of the
T.61 character set, it is recommended that the attribute should be
supplied as multi-valued attribute both in T.61 string and in a
transliterated PrintableString notation.
4.3 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
naming attributes should be publicly readable.
4.4 Selected Attributes
The section lists attributes together with a short description what
they should be used for and some examples.  The source of the
attributes is given in brackets.
Note that due to national legal restrictions on privacy issues it
might be forbidden to use certain attributes or that the search on
them is restricted. 
4.4.1 Personal Attributes
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.
The choice of a name depends on the culture as discussed in
section 3.4. When a commonName is selected as (part of) a RDN the
most often used form of the name should be selected. A firstname
should never be supplied only as an initial (unless, of course,
the source data does not include forenames). It is very important
to have its full value in order to be able to distinguish between
two similar entries. Sets of initials should not be concatenated
into a single "word", but be separated by spaces and/or "."
Format: Firstname [Initials] Lastname
Example: Steve Kille
Stephen E. Kille
The use of 'Lastname Firstname' is deprecated as explained in
favouriteDrink [RFC 1274]
The intention of this attribute is that it provides at least one
benign attribute which any user can create or modify, given a
suitable user interface, without having the unfortunate impact on
the directory service that follows from modifying an attribute
such as an e-mail address or telephone number.
Example: Pure Crystal Water
organizationalStatus [RFC 1274]
The Organisational Status attribute type specifies a category by
which a person is often referred to in an organisation. Examples
of usage in academia might include undergraduate student,
researcher, lecturer, etc.
A Directory administrator should consider carefully the
distinctions between this and the title and description
Example: undergraduate student
personalTitle [RFC 1274]
The usually used titles, especially academic ones. Excessive use
should be avoided.
Example: Prof. Dr.
roomNumber [RFC 1274]
The room where the person works, it will mostly be locally defined
how to write the room number, e.g., Building Floor Room.
Example: HLW B12
secretary [RFC 1274]
The secretary of the person. This is the Distinguished Name (DN)
of the secretary.
Example: CN=Beverly Pyke, O=ISODE Consortium, C=GB
Like with commonName it is a matter of culture what to use for
surname in case of a noble name, e.g., de Stefani, von Gunten.
Title describing the position, job title or function of an
Example: Manager - International Sales
userId [RFC 1274]
When an organisation has centrally managed user ids, it might make
sense to include it into the entry. It might also be used to form
a unique RDN for the person.
The password of the entry which allows the modification of the
entry, provided that the access control permits it. The password
should not be the same as any system password, unless it is sure
that nobody can read it. With the current implementations this is
mostly not guaranteed.
4.4.2 Organisational Attributes
associatedDomain [RFC 1274]
The Internet domain name for an organisation or one of its units.
Type of business an organisation, an organisational unit or
organisational person is involved in. The values could be chosen
from a thesaurus.
Example: Software Development
The name of the organisation. The value for the RDN should be
chosen according to section 3.3. Additional names like
abbreviations should be used for better search results.
Example: Uni Lausanne
Universite de Lausanne
Universit\c2e Lausanne (with a T.61 encoded umlaut)
University of Lausanne
The name of a part of the organisation. The value for the RDN
should be chosen according to section 3.3. Additional names like
abbreviations should be provided for better search results.
Example: Institut fuer Angewandte Mathematik
The person(s) in that role. This is the Distinguished Name of the
entry of the person(s).
Example: CN=Beverly Pyke, O=ISODE Consortium, C=GB
The currently available DUAs make no use this attribute. It seems
that it is not powerful enough for real usage. Experience is
needed before being able to give recommendations on how to
4.4.3 Local Attributes
Name of the place, village or town with values in local and other
languages as useful.
B\c3ale (with a T.61 encoded accented character) Basel
Name of the canton, county, department, province or state with
values in local and other languages as useful. If official and
commonly used abbreviations exist for the states, they should be
supplied as additional values
4.4.4 Miscellaneous Attributes
audio [RFC 1274]
The audio attribute uses a u-law encoded sound file as used by the
"play" utility on a Sun 4. According to RFC 1274 it is an interim
format. It may be useful to listen to the pronunciation of a name
which is otherwise unknown.
A short informal explanation of special interests of a person or
organisation. Overlap with businessCategory, organizationalStatus
and title should be avoided.
Example: Networking, distributed systems, OSI, implementation.
friendlyCountryName [RFC 1274]
The friendlyCountryName attribute type specifies names of
countries in human readable format. Especially the country name as
used in the major languages should be included as additional
values to help foreign users.
jpegPhoto [RFC 1488] 
A colour or grayscale picture encoded according to JPEG File
Interchange Format (JFIF). Thanks to compression the size of the
pictures is moderate. For persons it may show a portrait, for
organisations the company logo or a map on how to get there.
photo [RFC 1274]
The photo attribute is a b/w G3 fax encoded picture of an object.
The size of the photo should be in a sensible relation to the
informational value of it. This attribute will be replaced by
Reference to another closely related entry in the DIT, e.g., from
a room to the person using that room. It is the Distinguished Name
of the entry.
Example: CN=Beverly Pyke, O=ISODE Consortium, C=GB
4.4.5 MHS Attributes
The attribute uses internally an ASN.1 structure. The string
notation used for display purposes is implementation dependent.
This attribute is especially useful for an integrated X.400 user
agent since it gets the address in a directly usable format.
rfc822mailbox [RFC 1274]
E-Mail address in RFC 822 notation
textEncodedORAddress [RFC 1274]
X.400 e-mail address in string notation. The F.401 notation should
be used. This attribute shall disappear once the majority of the
DUAs support the mhsORAddresses attribute. The advantage of the
latter attribute is, that a configurable DUA could adjust the
syntax to the one needed by the local mailer, where
textencodedORAddress is just a string which will mostly have a
different syntax than the mailer expects.
Example: G=thomas; S=lenggenhager; OU1=gate; O=switch; \
P=switch; A=arcom; C=ch;
4.4.6 Postal Attributes
The full postal address (but not including the name) in
international notation, with up to 6 lines with 30 characters
The postalCode will be the same as used in the postalAddress (in
It shall be the street where the person has its office. Mostly, it
will be the street part of the postalAddress.
Example: Limmatquai 138
4.4.7 Telecom Attributes
telephoneNumber, facsimileTelephoneNumber & iSDNAddress [X.520]
The phone number in the international notation according to CCITT
E.123. The separator '-' instead of space may be used according to
the local habit, it should be used consistently within a country.
Format: "+" <country code> <national number> ["x" <extension>]
Example: +41 1 268 1540
The telex number in the international notation
Example: 817379, ch, ehhg
This section draws attention to two areas which frequently provoke
questions, and where it is felt that a consistent approach will be
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 use an
attribute type normally used for naming entries of the
object class of the main entry.
2. If the entry (aliased object) were placed where the alias
is, there should be no schema violation.
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.
 Barker, P., and S. Hardcastle-Kille, "The COSINE and Internet
X.500 schema", RFC 1274, Department of Computer Science,
University College London, November 1991.
 "The Directory --- Overview of concepts, models and services",
CCITT X.500 Series Recommendations, December 1988.
 The North American Directory Forum. "A Naming Scheme for C=US",
RFC 1255, NADF-175, NADF, September 1991.
 Michaelson, G., and M. Prior, "Naming Guidelines for the AARNet
X.500 Directory Service", RFC 1562, AEN-001, The University of
Queensland, The University of Adelaide, December 1993.
 Hardcastle-Kille, S., "Using the OSI Directory to achieve user
friendly naming", RFC 1484, Department of Computer Science,
University College London, July 1993.
 Barker, P., "Preparing data for inclusion in an X.500 Directory",
Research Note RN/92/41, Department of Computer Science,
University College London, May 1992.
 Jeunink, E., and E. Huizer, "Directory Services and Privacy
Issues", RARE WG-DATMAN, TF-LEGAL, Work in Progress, May 1993.
 Howes, T., Kille, S., Yeong, W., and C. Robbins, "The X.500
String Representation of Standard Attribute Syntaxes", RFC 1488,
University of Michigan, ISODE Consortium, Performance Systems
International, NeXor Ltd., July 1993.
7. Security Considerations
Security issues are not substantially discussed in this memo.