Network Working Group                               S. Hardcastle-Kille
Request for Comments: 1484                             ISODE Consortium
                                                              July 1993

                   Using the OSI Directory to achieve
                          User Friendly Naming
                           (OSI-DS 24 (v1.2))

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard.  Discussion and
   suggestions for improvement are requested.  Please refer to the
   current edition of the "IAB Official Protocol Standards" for the
   standardization state and status of this protocol.  Distribution of
   this memo is unlimited.

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

   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 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 [HK93], and it is intended that these specifications
   are compatible.  Please send comments to the author or to the
   discussion group: <osi-ds@CS.UCL.AC.UK>.

   1.  Why a notation is needed......................................  2
   2.  The Notation..................................................  3
   3.  Communicating Directory Names.................................  8
   4.  Matching a purported name.....................................  9
   4.1 Environment................................................... 10
   4.2 Matching...................................................... 12
   4.3 Top Level..................................................... 13
   4.4 Intermediate Level............................................ 14
   4.5 Bottom Level.................................................. 15
   5.  Examples...................................................... 15
   6.  Support required from the standard............................ 16
   7.  Support of OSI Services....................................... 16
   8.  Experience.................................................... 17
   9.  Relationship to other work.................................... 18
   10. Issues........................................................ 19
   11. References.................................................... 20
   12. Security Considerations....................................... 21
   13. Author's Address.............................................. 21
   A.  Pseudo-code for the matching algorithm ....................... 21

List of Figures

   1. Example usage of User Friendly Naming.......................... 18
   2. Matching Algorithm............................................. 25

List of Tables

   1. Local environment for private DUA.............................. 11
   2. Local environment for US Public DUA............................ 11

1. Why a notation is needed

   Many OSI Applications make use of Distinguished Names (DN) as defined
   in the OSI Directory [CCI88].  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 RFC1485 for representing
   distinguished names [HK93].  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.

2. The Notation

   The notation used in this specification is defined in [HK93].  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 [Kil90].  Some examples of the specification are given
   here.

   The author's User Friendly Name (UFN) might be written:

      Steve Hardcastle-Kille, Computer Science, University College
      London, GB

   or

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

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

      Steve Hardcastle-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

   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)

   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
         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,
      CN=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 local context).
   For example:

      Steve Hardcastle-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 [HK93].  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 Hardcastle-Kille, University College London, GB

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

      Steve Hardcastle-Kille, University College London

   Approximation

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

      Stephen Hardcastle-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 [HK93],
   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 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 [HK93].

      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.

      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
   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 name 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, the 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.

           +----------------------------------------------------+
           | 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

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

      Stephen Hardcastle-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 Hardcastle-
   Kille should be a good match of S. Hardcastle-Kille, S.E.
   Hardcastle-Kille or Steve Hardcastle-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.

      3. If there are only poor matches, prompt the user.  If the user
         accepts one or more match, 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
   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
   sensible. (It might be desirable to allow "*" as a part of the
   purported name notation).

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 in section
   4.1.

   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

   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
   Hardcastle-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.

   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

   in 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 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
   [Ros90], 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.

      -> 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

9. Relationship to other work

   Colin Robbin's work on the interface "Tom" and implementation of a
   distribution list interface strongly influenced this specification
   [KRRT90].

   Some of the ideas used here originally came from a UK Proposal to the
   ISO/CCITT Directory Group on "New Name Forms" [Kil89a].  This
   defined, and showed how to implement, four different types of names:

   Typed and Ordered

   The current Distinguished Name is a restricted 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
   [Neu89], and Peterson proposes the Profile system to provide this
   [Pet88].  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 born out by operational
   experience with OSI Directories [Kil89b].

   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.

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

11. References

   [CCI88]  The Directory --- overview of concepts, models and services,
            December 1988. CCITT X.500 Series Recommendations.

   [HK93]   S.E. Hardcastle-Kille. A string representation of
            distinguished names.  RFC 1485, Department of Computer
            Science, University College London, July 1993.

   [Kil89a] S.E. Kille. New name forms, May 1989.  ISO/IEC/JTC 21/
            WG4/N797 UK National Body Contribution to the Oslo Directory
            Meeting.

   [Kil89b] S.E. Kille. The THORN large scale pilot exercise.  Computer
            Networks and ISDN Systems, 16(1):143--145, January 1989.

   [Kil90]  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.

   [KRRT90] S.E. Kille, C.J. Robbins, M. Roe, and A. Turland. The ISO
            development environment:  User's manual (version 6.0),
            January 1990. Volume 5:  QUIPU.

   [Neu89]  G.W. Neufeld. Descriptive names in X.500.  In SIGCOMM 89
            Symposiun Communications Architectures and Protocols, pages
            64--71, September 1989.

   [Pet88]  L.L. Petersen. The profile naming service.  ACM Transactions
            on Computing Systems, 6(4):341--364, November 1988.

   [Ros90]  M.T. Rose. Realizing the White Pages using the OSI Directory
            Service. Technical Report 90--05--10--1, Performance Systems
            International, Inc., May 1990.

12. Security Considerations

Security issues are not discussed in this memo.

13. Author's Address

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

   Phone:+44-71-223-4062

   EMail:  S.Kille@ISODE.COM

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

   UFN: S. Hardcastle-Kille,
   ISODE Consortium, GB

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));
}
                                                                    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

                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 hists 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}));
}
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;
                                                                   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
______________________________________________________________________