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Network Working                                             S.E. Kille
Group                                                 ISODE Consortium
INTERNET-DRAFT                                           November 1994
Obsoletes:  RFC 1484                                Expires:  May 1995
                                                                 File:
                                draft-ietf-osids-user-friendly-dir-00.txt,ps





                  Using the OSI Directory to achieve

                         User Friendly Naming






Status of this Memo

This document is an Internet Draft.  Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups.  Note that other groups may also distribute
working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six months.
Internet Drafts may be updated, replaced, or obsoleted by other
documents at any time.  It is not appropriate to use Internet Drafts
as reference material or to cite them other than as a ``working
draft'' or ``work in progress.''
Please check the I-D abstract listing contained in each Internet Draft
directory to learn the current status of this or any other Internet
Draft.

Abstract
The OSI Directory has user friendly naming as a goal.  A simple minded
usage of the directory does not achieve this.  Two aspects not
achieved are:


 o  A user oriented notation

 o  Guessability




INTERNET--DRAFT           User Friendly Naming           November 1994


This proposal sets out some conventions for representing names in a
friendly manner, and shows how this can be used to achieve really
friendly naming.  This then leads to a specification of a standard
format for representing names, and to procedures to resolve them.
This leads to a specification which allows directory names to be
communicated between humans.  The format in this specification is
identical to that defined in [5], and it is intended that these
specifications are compatible.
This draft document will be submitted to the RFC editor as a protocol
standard.  Distribution of this memo is unlimited.  Please send
comments to the author or to the discussion group
<osi-ds@CS.UCL.AC.UK>.

































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Contents

1   Why a notation is needed                                         4

2   The Notation                                                     5


3   Communicating Directory Names                                    9

4   Matching a purported name                                       11

    4.1    Environment   .   .   .   .   .   .   .   .   .   .      12
    4.2    Matching  .   .   .   .   .   .   .   .   .   .   .      12
    4.3    Top Level     .   .   .   .   .   .   .   .   .   .      15

    4.4    Intermediate Level    .   .   .   .   .   .   .   .      15
    4.5    Bottom Level  .   .   .   .   .   .   .   .   .   .      17

5   Examples                                                        17


6   Support required from the standard                              19

7   Support of OSI Services                                         19


8   Experience                                                      20

9   Relationship to other work                                      20

10  Issues                                                          22


11  Security Considerations                                         23

12  Author's Address                                                24


A   Pseudo-code for the matching algorithm                          25






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List of Figures

    1      Example usage of User Friendly Naming     .   .   .      21
    2      Matching Algorithm    .   .   .   .   .   .   .   .      29


List of Tables


    1      Local environment for private DUA     .   .   .   .      13
    2      Local environment for US Public DUA   .   .   .   .      13


































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1  Why a notation is needed

Many OSI Applications make use of Distinguished Names (DN) as defined
in the OSI Directory [1].  The main reason for having a notation for
name format is to interact with a user interface.  This specification
is coming dangerously close to the sin of standardising interfaces.
However, there are aspects of presentation which it is desirable to
standardise.
It is important to have a common format to be able to conveniently
refer to names.  This might be done to represent a directory name on a
business card or in an email message.  There is a need for a format to
support human to human communication, which must be string based (not
ASN.1) and user oriented.

In very many cases, a user will be required to input a name.  This
notation is designed to allow this to happen in a uniform manner
across many user interfaces.  The intention is that the name can just
be typed in.  There should not be any need to engage in form filling
or complex dialogue.
It should be possible to take the ``human'' description given at the
meeting, and use it directly.  The means in which this happens will
become clear later.
This approach uses the syntax defined in [5] for representing
distinguished names.  By relaxing some of the constraints on this
specification, it is argued that a more user oriented specification is
produced.  However, this syntax cannot be mapped algorithmically onto
a distinguished name without the use of a directory.

This notation is targeted towards a general user oriented system, and
in particular to represent the names of humans.  Other syntaxes may be
more appropriate for other uses of the directory.  For example, the
OSF Syntax may be more appropriate for some system oriented uses.
(The OSF Syntax uses ``/'' as a separator, and forms names in a manner
intended to resemble UNIX filenames).
This notation is targeted towards names which follow a particular DIT
structure:  organisationally oriented.  This may make it inappropriate
for some types of application.  There may be a requirement to extend
this notation to deal more cleanly with fully geographical names.

This approach effectively defines a definition of descriptive names on
top of the primitive names defined by the OSI Directory.




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2  The Notation

The notation used in this specification is defined in [5].  This
notation defines an unambiguous representation of distinguished name,
and this specification is designed to be used in conjunction with this
format.  Both specifications arise from the same piece of research
work [4].  Some examples of the specification are given here.
The author's User Friendly Name (UFN) might be written:


Steve Kille, Computer Science, University College London, GB

or


S. Kille, Computer Science, University College London, GB

This may be folded, perhaps to display in multi-column format.  For
example:


Steve Kille,
Computer Science,
University College London,
GB


Another UFN might be:

Christian Huitema, INRIA, FR


or

James Hacker,
Basingstoke,
Widget Inc,
GB


The final example shows quoting of a comma in an Organisation name:

L. Eagle, "Sue, Grabbit and Runn", GB


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A purported name is what a user supplies to an interface for
resolution into one or more distinguished names.  A system should
almost always store a name as a distinguished name.  This will be more
efficient, and avoid problems with purported names which become
ambiguous when a new name appears.  A user interface may display a
distinguished name, using the distinguished name notation.  However,
it may display a purported name in cases where this will be more
pleasing to the user.  Examples of this might be:

 o  Omission of the higher components of the distinguished name are
    not displayed (abbreviation).

 o  Omission of attribute types, where the type is unlikely to be
    needed to resolve ambiguity.


The ways in which a purported name may vary from a distinguished name
are now described:

Type Omission There are two cases of this.

     o  Schema defaulting.  In this case, although the type is not
        present, a schema defaulting is used to deduce the type.  The
        first two types of schema defaulting may be used to deduce a
        distinguished name without the use of the directory.  The use
        of schema defaulting may be useful to improve the performance
        of UFN resolution.  The types of schema defaulting are:

        --  Default Schema

        --  Context Dependent Default Schema

        --  Data Dependent Default Schema

     o  Omission of the type to be resolved by searching.

Default Schema The attribute type of an attribute may always be
    present.  This may be done to emphasise the type structure of a
    name.  In some cases, the typing may be omitted.  This is done in
    a way so that in many common cases, no attribute types are needed.
    The following type hierarchy (schema) is assumed:

    Common Name, (((Organisational Unit)*,  Organisation,) Country)


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    Explicitly typed RDNs may be inserted into this hierarchy at any
    point.  The least significant component is always of type Common
    Name.  Other types follow the defined organisational hierarchy.
    The following are equivalent:

    Filestore Access, Bells, Computer Science,
    University College London, GB

    and

    CN=Filestore Access, OU=Bells, OU=Computer Science,
    O=University College London, C=GB

    To interpet a distinguished name presented in this format, with
    some or all of the attributes with the type not specified, the
    types are derived according to the type hierarchy by the following
    algorithm:

    1.  If the first attribute type is not specified, it is
        CommonName.

    2.  If the last attribute type is not specified, it is Country.

    3.  If there is no organisation explicitly specified, the last
        attribute with type not specified is of type Organisation.

    4.  Any remaining attribute with type unspecified must be before
        an Organisation or OrganisationalUnit attribute, and is of
        type OrganisationalUnit.


    To take a distinguished name, and generate a name of this format
    with attribute types omitted, the following steps are followed.

    1.  If the first attribute is of type CommonName, the type may be
        omitted.

    2.  If the last attribute is of type Country, the type may be
        omitted.

    3.  If the last attribute is of type Country, the last
        Organisation attribute may have the type omitted.

    4.  All attributes of type OrganisationalUnit may have the type

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        omitted, unless they are after an Organisation attribute or
        the first attribute is of type OrganisationalUnit.

Context Dependent Default Schema The distinguished name notation
    defines a fixed schema for type defaulting.  It may be useful to
    have different defaults in different contexts.  For example, the
    defaulting convention may be applied in a modified fashion to
    objects which are known not to be common name objects.  This will
    always be followed if the least significant component is
    explicitly typed.  In this case, the following hierarchy is
    followed:

    ((Organisational Unit)*,  Organisation,) Country

Data Dependent Defaulting There are cases where it would be optimal
    to default according to the data.  For example, in:

    Einar Stefferud, Network Management Associates, CA, US


    It would be useful to default ``CA'' to type State.  This might be
    done by defaulting all two letter attributes under C=US to type
    State.

General Defaulting A type may be omitted in cases where it does not
    follow a default schema hierarchy, and then type variants can be
    explored by searching.  Thus a distinguished name could be
    represented by a uniquely matching purported name.  For example,

    James Hacker,
    Basingstoke,
    Widget Inc,
    GB

    Would match the distinguished name:


    CN=James Hacker,
    L=Basingstoke,
    O=Widget Inc,
    C=GB

Abbreviation Some of the more significant components of the DN will
    be omitted, and then defaulted in some way (e.g., relative to a

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    local context).  For example:

    Steve Kille

    Could be interpreted in the context of an organisational default.

Local Type Keywords Local values can be used to identify types, in
    addition to the keywords defined in [5].  For example,
    ``Organisation'' may be recognised as an alternative to ``O''.

Component Omission An intermediate component of the name may be
    omitted.  Typically this will be an organisational unit.  For
    example:

    Steve Kille, University College London, GB

    In some cases, this can be combined with abbreviation.  For
    example:

    Steve Kille, University College London


Approximation Approximate renditions or alternate values of one or
    more of the components will be supplied.  For example:

    Stephen Kille, CS, UCL, GB

    or

    Steve Keill, Comp Sci, Univarstiy College London, GB

Friendly Country A ``friendly country name'' can be used instead of
    the ISO 3166 two letter code.  For example:  UK; USA; France;
    Deutchland.


3  Communicating Directory Names


A goal of this standard is to provide a means of communicating
directory names.  Two approaches are given, one defined in [5], and
the other here.  A future version of these specifications may contain
only one of these approaches, or recommend use of one approach.  The
approach can usually be distinguished implicitly, as types are

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normally omitted in the UFN approach, and are always present in the
Distinguished Name approach.  No recommendation is made here, but the
merits of each approach is given.

1.  Distinguished Name or DN. A representation of the distinguished
    name, according to the specification of [5].

2.  User Friendly Name or UFN. A purported name, which is expected to
    unambiguously resolve onto the distinguished name.


When a UFN is communicated, a form which should efficiently and
unambiguously resolve onto a distinguished name should be chosen.
Thus it is reasonable to omit types, or to use alternate values which
will unambiguously identify the entry in question (e.g., by use of an
alternate value of the RDN attribute type).  It is not reasonable to
use keys which are (or are likely to become) ambiguous.
The approach used should be implicit from the context, rather than
wired into the syntax.  The terms ``Directory Name'' and ``X.500
Name'' should be used to refer to a name which might be either a DN or
UFN. An example of appropriate usage of both forms is given in the
Section which defines the Author's location in Section 12.
Advantages of communicating the DN are:


 o  The Distinguished Name is an unambiguous and stable reference to
    the user.

 o  The DN will be used efficiently by the directory to obtain
    information.

Advantages of communicating the UFN are:


 o  Redundant type information can be omitted (e.g., ``California'',
    rather than ``State=California'', where there is known to be no
    ambiguity.

 o  Alternate values can be used to identify a component.  This might
    be used to select a value which is meaningful to the recipient, or
    to use a shorter form of the name.  Often the uniqueness
    requirements of registration will lead to long names, which users
    will wish to avoid.


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 o  Levels of the hierarchy may be omitted.  For example in a very
    small organisation, where a level of hierarchy has been used to
    represent company structure, and the person has a unique name
    within the organisation.

Where UFN form is used, it is important to specify an unambiguous
form.  In some ways, this is analogous to writing a postal address.
There are many legal ways to write it.  Care needs to be taken to make
the address unambiguous.


4  Matching a purported name

The following approach specifies a default algorithm to be used with
the User Friendly Naming approach.  It is appropriate to modify this
algorithm, and future specifications may propose alternative
algorithms.  Two simple algorithms are noted in passing, which may be
useful in some contexts:


1.  Use type omission only, but otherwise require the value of the RDN
    attribute to be present.

2.  Require each RDN to be identified as in 1), or by an exact match
    on an alternate value of the RDN attribute.

These algorithms do not offer the flexibility of the default algorithm
proposed, but give many of the benefits of the approach in a very
simple manner.

The major utility of the purported name is to provide the important
``user friendly'' characteristic of guessability.  A user will supply
a purported name to a user interface, and this will be resolved onto a
distinguished name.  When a user supplies a purported name there is a
need to derive the DN. In most cases, it should be possible to derive
a single name from the purported name.  In some cases, ambiguities
will arise and the user will be prompted to select from a multiple
matches.  This should also be the case where a component of the name
did not ``match very well''.
There is an assumption that the user will simply enter the name
correctly.  The purported name variants are designed to make this
happen!  There is no need for fancy window based interfaces or form
filling for many applications of the directory.  Note that the fancy


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interfaces still have a role for browsing, and for more complex
matching.  This type of naming is to deal with cases where information
on a known user is desired and keyed on the user's name.

4.1  Environment


All matches occur in the context of a local environment.  The local
environment defines a sequence of names of a non-leaf objects in the
DIT. This environment effectively defines a list of acceptable name
abbreviations where the DUA is employed.  The environment should be
controllable by the individual user.  It also defines an order in
which to operate.
This list is defined in the context of the number of name components
supplied.  This allows varying heuristics, depending on the
environment, to make the approach have the ``right'' behaviour.
In most cases, the environment will start at a local point in the DIT,
and move upwards.  Examples are given in Tables 1 and 2.  Table 1
shows an example for a typical local DUA, which has the following
characteristics:


One component Assumed first to be a user in the department, then a
    user or department within the university, then a national
    organisation, and finally a country.

Two components Most significant component is first assumed to be a
    national organisation, then a department (this might be reversed
    in some organisations), and finally a country.

Three or more components The most significant component is first
    assumed to be a country, then a national organisation, and finally
    a department.


4.2  Matching


A purported name will be supplied, usually with a small number of
components.  This will be matched in the context of an environment.
Where there are multiple components to be matched, these should be
matched sequentially.  If an unambiguous DN is determined, the match
continues as if the full DN had been supplied.  For example if


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          Number of   Environment
         _Components_________________________________________
          1           Physics, University College London, GB
                      University College London, GB
                      GB
         _____________--_____________________________________
          2           GB
                      University College London, GB
         _____________--_____________________________________
          3+          --
                      GB
                      University College London, GB



             Table 1:  Local environment for private DUA









                       Number of   Environment
                      _Components______________
                       1,2         US
                                   CA
                      _____________--__________
                       3+          --
                                   US
                                   CA


            Table 2:  Local environment for US Public DUA





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    Stephen Kille, UCL

is being matched in the context of environment GB, first UCL is
resolved to the distinguished name:


    University College London, GB

Then the next component of the purported name is taken to determine
the final name.  If there is an ambiguity (e.g., if UCL had made two
matches, both paths are explored to see if the ambiguity can be
resolved.  Eventually a set of names will be passed back to the user.

Each component of the environment is taken in turn.  If the purported
name has more components than the maximum depth, the environment
element is skipped.  The advantage of this will be seen in the example
given later.
A match of a name is considered to have three levels:

Exact A DN is specified exactly

Good Initially, a match should be considered good if it is
    unambiguous, and exactly matches an attribute value in the entry.
    For human names, a looser metric is probably desirable (e.g.,
    S Kille should be a good match of S. Kille, S.E. Kille or Steve
    Kille even if these are not explicit alternate values).

Poor Any other substring or approximate match


Following a match, the reference can be followed, or the user
prompted.  If there are multiple matches, more than one path may be
followed.  There is also a shift/reduce type of choice:  should any
partial matches be followed or should the next element of the
environment be tried.  The following heuristics are suggested, which
may be modified in the light of experience.  The overall aim is to
resolve cleanly specified names with a minimum of fuss, but give
sufficient user control to prevent undue searching and delay.


1.  Always follow an exact match.

2.  Follow all good matches if there are no exact matches.


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3.  If there are only poor matches, prompt the user.  If the user
    accepts one or more matches, they can be considered as good.  If
    all are rejected, this can be treated as no matches.

4.  Automatically move to the next element of the environment if no
    matches are found.

When the final component is matched, a set of names will be
identified.  If none are identified, proceed to the next environment
element.  If the user rejects all of the names, processing of the next
environment element should be confirmed.

The exact approach to matching will depend on the level of the tree at
which matching is being done.  We can now consider how attributes are
matched at various levels of the DIT.
There is an issue of approximate matching.  Sometimes it helps, and
sometimes just returns many spurious matches.  When a search is
requested, all relevant attributes should be returned, so that
distinguished and non-distinguished values can be looked at.  This
will allow a distinction to be made between good and poor matches.  It
is important that where, for example, an acronym exactly matches an
organisation, that the user is not prompted about other organisations
where it matches as a substring.

4.3  Top Level


In this case, a match is being done at the root of the DIT. Three
approaches are suggested, dependent on the length of supplied name.
All lead to a single level search of the top level of the DIT.

Exactly 2 This is assumed to be a 3166 two letter country code, or an
    exact match on a friendly country or organisation (e.g., UK or
    UN). Do exact match on country and friendly country.

Greater than 2 Make an approximate and substring match on friendly
    country and organisation.


4.4  Intermediate Level

Once the root level has been dealt with, intermediate levels will be
looking for organisational components (Organisation, Locality, Org


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Unit).  In some cases, private schema control will allow the system to
determine which is at the next level.  In general this will not be
possible.  In each case, make a substring and approximate match search
of one level.  The choice depends on the base object used in the
search.

1.  If DN has no Organisation or Locality, filter on Organisation and
    Locality.

2.  If DN has Org Unit, filter on Org Unit.

3.  If DN has Organisation, filter on Locality and Org Unit.

4.  If DN has Locality, filter on Organisation.


These allow some optimisation, based on legal choices of schema.
Keeping filters short is usually desirable to improve performance.
A few examples of this, where a base object has been determined
(either by being the environment or by partial resolution of a
purported name), and the next element of a purported name is being
considered.  This will generate a single level search.  What varies is
the types being filtered against.  If the DN is:


University College London, GB

The search should be for Org Unit or Locality.  If the DN is:


Organisation=UN

the search should be for Org Unit or Locality.

There may be some improvements with respect to very short keys.  Not
making approximate or substring matches in these cases seems
sensible1.
----------------------------
    1. It might be desirable to allow ``*'' as a part of the purported
name notation





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4.5  Bottom Level

The ``Bottom Level'' is to deal with leaf entries in the DIT. This
will often be a person, but may also be a role, an application entity
or something else.
The last component of a purported name may either reference a leaf or
non-leaf.  For this reason, both should be tested for.  As a
heuristic, if the base object for the search has two or more
components it should be tested first as a bottom level name and then
intermediate.  Reverse this for shorter names.  This optimises for the
(normal) case of non-leaves high up the tree and leaves low down the
tree.

For bottom level names, make an approximate and substring match
against Common Name, Surname, and User ID. Where common name is looked
for, a full subtree search will be used when at the second level of
the DIT or lower, otherwise a single level search.
For example, if I have resolved a purported name to the distinguished
name


University College London, GB

and have a single component Bloggs, this will generate a subtree
search.


5  Examples

This is all somewhat confusing, and a few examples are given.  These
are all in the context of the environment shown in Table 1 on Page 13.

If ``Joe Bloggs'' is supplied, a subtree search of

Physics, University College London, GB


will be made, and the user prompted for ``Joseph Z. Bloggs'' as the
only possible match.
If ``Computer Science'' is supplied, first


Physics, University College London, GB


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will be searched, and the user will reject the approximate match of
``Colin Skin''.  Then a subtree search of

University College London, GB


will be made, looking for a person.  Then a single level search will
be made looking for Org Unit, and

Computer Science, University College London, GB


will be returned without prompting (exact match).
Supplying ``Steve Kille'' will lead to a failed subtree search of


Physics, University College London, GB

and lead straight to a subtree search of


University College London, GB

This will lead to an exact value match, and so a single entry returned
without prompting.

If ``Andrew Findlay, Brunel'' is supplied, the first element of the
environment will be skipped, single level search of ``Brunel'' under
``GB' will find:

Brunel University, GB


and a subtree search for ``Andrew Findlay'' initiated.  This will
yield

Andrew Findlay, Computing and Media Services, Brunel University, GB

Dr A J Findlay, Manufacturing and Engineering Systems,
Brunel University, GB


and the user will be prompted with a choice.


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This approach shows how a simple format of this nature will ``do the
right thing'' in many cases.


6  Support required from the standard

Fortunately, all that is needed is there!  It would be useful to have
``friendly country name'' as a standard attribute.


7  Support of OSI Services

The major focus of this work has been to provide a mechanism for
identifying Organisations and Users.  A related function is to
identify applications.  Where the Application is identified by an AET
(Application Entity Title) with an RDN of Common Name, this
specification leads to a natural usage.  For example, if a filestore
is named ``gannet'', then this could easily be identified by the name:


Gannet, Computer Laboratory, Cambridge University, GB

In normal usage, this might lead to access (using a purported name)
of:


FTAM gannet,cambridge

A second type of access is where the user identifies an Organisation
(Organisational Unit), and expects to obtain a default service.  The
service is implied by the application, and should not require any
additional naming as far as the user is concerned.  It is proposed
that this is supported by User Friendly Naming in the following way.


1.  Determine that the purported name identifies a non-leaf object,
    which is of object class Organisation or Organisational Unit or
    Locality.

2.  Perform a single level search for Application Entities which
    support the required application contexts.  This assumes that all
    services which are supporting default access for the organisation
    are registered at one level below (possibly by the use of
    aliases), and that other services (specific machines or parts of

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    the organisation) are represented further down the tree.  This
    seems to be a reasonable layout, and its utility can be evaluated
    by experiment.


8  Experience

An experimental implementation of this has been written by Colin
Robbins.  The example in Figure 1 shows that it can be very effective
at locating known individuals with a minimum of effort.  This code has
been deployed within the ``FRED'' interface of the PSI Pilot [9], and
within an prototype interface for managing distribution lists.  The
user reaction has been favourable:
Some issues have arisen from this experience:


 o  Where there is more than one level of Organisational Unit, and the
    user guesses one which is not immediately below the organisation,
    the algorithm works badly.  There does not appear to be an easy
    fix for this.  It is not clear if this is a serious deficiency.

 o  Substring searching is currently done with leading and trailing
    wildcards.  As many implementations will not implement leading
    wildcards efficiently, it may be preferable to only use trailing
    wildcards.  The effect of this on the algorithm needs to be
    investigated.

Implementors of this specification are encouraged to investigate
variants of the basic algorithm.  A final specification should depend
on experience with such variants.


9  Relationship to other work


Colin Robbin's work on the interface ``Tom'' and implementation of a
distribution list interface strongly influenced this specification
[6].
Some of the ideas used here originally came from a UK Proposal to the
ISO/CCITT Directory Group on ``New Name Forms'' [2].  This defined,
and showed how to implement, four different types of names:


Typed and Ordered The current Distinguished Name is a restricted

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-> t hales, csiro, australia
Found good match(es) for 'australia'
Found exact match(es) for 'csiro'
Please select from the following:
   Trevor Hales, OC, HPCC, DIT, IICT, CSIRO, AU [y/n] ? y
The following were matched...
   Trevor Hales, OC, HPCC, DIT, IICT, CSIRO, AU

-> g michaelson, queensland, au
Found exact match(es) for 'au'
Please select from the following:
   University of Queensland, AU [y/n] ? y
   Axolotl, AU [y/n] ? n
Please select from the following:
   George Michaelson, Prentice Computer Centre, University of Queensland, AU
[y/n] ? y
   Manager, University of Queensland, AU [y/n] ? n
The following were matched...
   George Michaelson, Prentice Computer Centre, University of Queensland, AU

-> r needham, cambridge
Found good match(es) for 'cambridge'
Please select from the following:
   Roger Needham, Computer Lab, Cambridge University [y/n] ? y
The following were matched...
   Roger Needham, Computer Lab, Cambridge University

-> kirstein
Found good match(es) for 'kirstein'
The following were matched...
   Peter Kirstein




           Figure 1:  Example usage of User Friendly Naming





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    example of this type of name.

Untyped and Ordered This is the type of name proposed here (with some
    extensions to allow optional typing).  It is seen as meeting the
    key user requirement of disliking typed names, and is efficient to
    implement.

Typed and Unordered This sort of name is proposed by others as the
    key basis for user friendly naming.  Neufeld shows how X.500 can
    be used to provide this [7], and Peterson proposes the Profile
    system to provide this [8].  The author contends that whilst typed
    naming is interesting for some types of searching (e.g., yellow
    page searching), it is less desirable for naming objects.  This is
    borne out by operational experience with OSI Directories [3].

Untyped and Unordered Surprisingly this form of name can be supported
    quite easily.  However, a considerable gain in efficiency can be
    achieved by requiring ordering.  In practice, users can supply
    this easily.  Therefore, this type of name is not proposed.


10  Issues

The following issues are noted, which would need to be resolved before
this document is progressed as an Internet Standard.


Potential Ambiguity Whilst the intention of the notation is to allow
    for specification of alternate values, it inherently allows for
    ambiguous names to be specified.  It needs to be demonstrated that
    problems of this characteristic are outweighed by other benefits
    of the notation.

Utility Determine that the specification is being implemented and
    used.

Performance Measurements on the performance implications of using
    this approach should be made.

Alogrithm The utility of the algorithm, and possible variants, should
    be investigated.




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This format, and the procedures for resolving purported names, should
be evolved to an Internet Standard.  The syntax can be expected to be
stable.  In light of experience, the algorithm for resolving purported
names may be changed.


References

[1] The Directory --- overview of concepts, models and services,
    1993. CCITT X.500 Series Recommendations.

[2] S.E. Kille. New name forms, May 1989.  ISO/IEC/JTC 21/ WG4/N797 UK
    National Body Contribution to the Oslo Directory Meeting.

[3] S.E. Kille. The THORN large scale pilot exercise.  Computer
    Networks and ISDN Systems, 16(1):143--145, January 1989.

[4] S.E. Kille. Using the OSI directory to achieve user friendly
    naming. Research Note RN/20/29, Department of Computer Science,
    University College London, February 1990.

[5] S.E. Kille. A string representation of distinguished name.
    Request for Comments in preparation, ISODE Consortium, November
    1994.

[6] S.E. Kille and C.J. Robbins. The ISO development environment:
    User's manual (version 7.0), July 1991. Volume 5:  QUIPU.

[7] G.W. Neufeld. Descriptive names in X.500.  In SIGCOMM 89 Symposiun
    Communications Architectures and Protocols, pages 64--71,
    September 1989.

[8] L.L. Petersen. The profile naming service.  ACM Transactions on
    Computing Systems, 6(4):341--364, November 1988.

[9] M.T. Rose. Realizing the White Pages using the OSI Directory
    Service. Technical Report 90--05--10--1, Performance Systems
    International, Inc., May 1990.


11  Security Considerations

Security considerations are not discussed in this INTERNET--DRAFT.


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12  Author's Address

    Steve Kille
    ISODE Consortium
    The Dome
    The Square
    Richmond, Surrey
    TW9 1DT
    England


    Phone:+44-181-332-9091

    EMail:  S.Kille@ISODE.COM


    DN: CN=Steve Kille,
    O=ISODE Consortium, C=GB

    UFN: S. Kille,
    ISODE Consortium, GB
























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A  Pseudo-code for the matching algorithm

The following pseudo-code is intended to clarify the matching
algorithm.  The language uses ASN.1 data types, with flow control
`C'-like,_but_with_keywords_upper--cased.______________________________



PurportedName ::= SEQUENCE OF String
                -- simplication, as attribute types can optionally be
                -- specified

                -- Each element of the Purported Name is a string
                -- which has been parsed from the BNF

Attribute ::= SEQUENCE {                                            10
        type OBJECT IDENTIFIER,
        value ANY }

RDN ::= Attribute -- simplification, as can be multi-value

DN ::= SEQUENCE OF RDN

Environment ::= SEQUENCE OF DN

                                                                    20
EnvironmentList ::= SEQUENCE OF SEQUENCE {
                        lower-bound INTEGER,
                        upper-bound INTEGER,
                        environment Environment }


friendlyMatch(p:  PurportedName; el:  EnvironmentList):    SET OF DN
{
                                -- Find correct environment
                                                                    30
        IF length(el) == 0 THEN return(NULL);

        IF length(p) <= head(el).upper-bound
                        && length(p) >= head(el).lower-bound THEN
                return envMatch (p, head(el).environment);
        ELSE
                return(friendlyMatch(p, tail(el));


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}

                                                                    40
envMatch(p:  PurportedName; e:  Environment):    SET OF DN
{
                                -- Check elements of environment
                                -- in the defined order

        matches:  SET OF DN;

        IF length(e) == 0 THEN return(NULL);

        matches = purportedMatch(head(e).DN, p)                     50
        IF matches != NULL THEN
                return(matches);
        ELSE
                return(envMatch(p, tail(e));
}


purportedMatch(base:  DN; p:  PurportedName):  SET OF DN
{
        s:  String = head(p);                                       60
        matches:  SET OF DN = NULL;

        IF length(p) == 1 THEN
                IF length(base) == 0 THEN
                        IF (matches = rootSearch(s)) != NULL THEN
                                return(matches);
                        ELSE return(leafSearch(base, s, one-level);
                ELSE IF length(base) == 1 THEN
                        IF (matches = intSearch(base, s)) != NULL THEN
                                return(matches);                    70
                        ELSE return(leafSearch(base, s, one-level);
                ELSE
                        IF (matches = leafSearch(base, s, subtree)) != NULL THEN
                                return(matches);
                        ELSE return(intsearch(base, s);


        IF length(base) == 0 THEN
                FOR x IN rootSearch(s) DO
                        matches += (purportedMatch(x, tail(p));     80
        ELSE

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                FOR x IN intSearch(base, s) DO
                        matches += (purportedMatch(x, tail(p));
        return(matches);
}


-- General.    Might need to tighten the filter for short strings,
-- in order to stop being flooded.    Alternatively, this could be
-- done if the loose search hits a size limit                       90

rootSearch(s:  String):  SET OF DN
{
        IF length(s) == 2 THEN
                return(search(NULL, one-level, s, {CountryName,
                        FriendlyCountryName, OrganizationName},
                        {exact}, {Country, Organisation}));
                        -- test exact match only
                        -- probably a country code
        ELSE                                                       100
                return(search(NULL, one-level, s, {OrganizationName,
                        FriendlyCountryName}, {substring, approx},
                        {Country, Organisation}));
}


intSearch( base:  DN; s:  String)
{
        IF present(base, OrgUnitName) THEN
                return(search(base, one-level, s, {OrgUnitName},   110
                        {substring, approx}, {OrgUnit}));
        ELSE IF present(base, OrganisationName) THEN
                return(search(base, one-level, s, {OrgUnitName,
                        LocalityName}, {substring, approx},
                        {Organization, OrgUnit, Locality}));
        ELSE IF present(base, LocalityName) THEN
                return(search(base, one-level, s, {OrganisationName},
                        {substring, approx}, {Locality});
        ELSE
                return(search(base, one-level, s, {OrganisationName,120
                        LocalityName}, {substring, approx},
                        {Organisation, Locality}));
}



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present(d:  DN; t:  AttributeType):  BOOLEAN
{
        FOR x IN d DO
                IF x.type == t THEN return(TRUE);
        return(FALSE);                                             130
}

SearchScope := ENUMERATED (base-object, one-level, subtree)

leafSearch(base:  DN; s:  String; search-scope:  SearchScope)
{
        return(search(base, search-scope, s, {CommonName, Surname,
                UserId}, {substring, approx}));
}
                                                                   140

search(base:  DN; search-scope:  SearchScope; s:  string;
        alist SET OF AttributeType; matchtypes SET OF MatchType
        objectClasses SET OF ObjectClass OPTIONAL): SET OF DN
{
        -- mapped onto Directory Search, with OR conjunction
        -- of filter items

        return dNSelect (s, search-results, alist);
}                                                                  150

read(base:  DN; alist SET OF AttributeType):  SET OF Attribute;
{
        -- mapped onto Directory Read
        -- Types repeated to deal with multiple values
        -- This would be implemented by returning selected info
        -- with the search operation
}

dNSelect(s:  String; dlist SET OF DN; alist:  SET OF AttributeType):16SET0OF DN
{
        exact, good:  SET OF DN;

        FOR x IN dlist DO
                IF last(DN).Value == s THEN
                        exact += x;
                ELSE IF FOR y IN read(x, alist) DO
                        IF y.value == s THEN
                                good += x;

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                                                                   170

        IF exact != NULL THEN return(exact);
        IF good != NULL THEN return(good);
        return(userQuery(dlist));
}


userQuery(dlist SET OF DN): SET OF DN
{
        -- pass back up for manual checking                        180
        -- user can strip all matches to force progres....
}


head()    -- return first element of list
tail()    -- return list with first element removed
length()  -- return size of list
last()    -- return last element of list

____________________Figure_2:__Matching_Algorithm______________________
























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