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Versions: 00 01 02 03 04 05 06                                          
Internet Draft                                            J. Klensin
Document: draft-klensin-dns-search-05.txt
Expires: May 2003                                   03 November 2002

                  A Search-based access model for the DNS

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [RFC2026].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   The list of Internet-Draft Shadow Directories can be accessed at


   This memo discusses strategies for supporting "DNS searching" --
   finding of names in the DNS, or references that will ultimately point
   to DNS names, by a mechanism layered above the DNS itself that
   permits fuzzy matching, selection that uses attributes or facets, and
   use of descriptive terms. Demand for these facilities appear to be
   increasing with growth in the Internet (and especially the web) and
   with requirements to move beyond the restricted subset of ASCII names
   that have been the traditional contents of DNS "Class=IN".  This
   document proposes a three-level system for access to DNS names in
   which the upper two levels involve search, rather than lookup
   (exactly known target), functions. It also discusses some of the
   issues and challenges in completing the design of, and deploying,
   such a system.

Table of Contents

   1  Introduction and Executive Summary ....
   2  A three (or four) search-layer environment ....
   2.1  Base Layer Identifiers -- a lookup system and the DNS. ....
   2.2  A Globally-accessible Search Component for Names ....
   2.2.1  The facets....
   2.2.2  The name string....
   2.2.3  Case matching....
   2.2.4  More complex character matching....
   2.2.5  Query formation and specification....

   2.2.6  Imprecise matching....
   2.2.7  Registration rules and query rules....
   2.2.8  Server location....
   2.3  The Third Component: Locality and/or content-domain-specific
   data and mechanisms....
   2.4  The Non-directory Search Component: free-text searching
   2.5  Database and searching differentiation ....
   3  Context and Model Details: Global faceted search ....
   3.1  The data search and access model ....
   3.2  Uniqueness of name structures in global faceted search ....
   3.2.1  The case for unique names....
   3.2.2  Non-unique names....
   3.2.3  A middle ground approach: artificial uniqueness....
   3.3  Sources for controlled-vocabulary facets ("attributes") ....
   3.3.1  Discussion of language identification....
   3.3.2  Discussion of geographical identification....
   3.3.3  Discussion of Industry Types....
   3.4  Deployment against the existing DNS base ....
   3.5  Thoughts about user interfaces (UIs) ....
   3.6  Implementation models ....
   3.6.1  Calling and returning values....
   3.6.2  The cache model....
   3.6.3  An example: Looking at Chinese Traditional-Simplified Mappings
   3.6.4  An example: Distance functions and Latin-based alphabets....
   3.7  Older applications ....
   4  Context and model details: Localized and Topical Searching ....
   5  Comparisons to existing and proposed technology ....
   5.1  The IDN Strawman ....
   5.2  "Keyword" systems ....
   5.3  Client-side and server-side solutions ....
   6  Comments on business models ....
   6.1  Faceted global searching ....
   6.1.1  Facet listings and identification....
   6.1.2  Registration and searching....
   6.2  Localized and topical databases and searching ....
   7  Glossary ....
   8  Summary ....
   9  IANA Considerations and related topics ....
   10   Security Considerations ....
   11   References ....
   12   Acknowledgments ....
   13   Author's Address ....
   14   Major changes between version 04 and 05 ....
   15   Placeholders ....

1  Introduction and Executive Summary

   The notion of "DNS searching" is somewhat of an oxymoron: the DNS is
   structured to only perform exact lookups of structured strings of
   labels.  But, as discussed elsewhere, there is considerable demand
   for searching facilities -- partial and fuzzy matching, selection
   that uses attributes or facets, and searching using descriptive
   terms-- and that demand appears to be increasing with growth in the
   Internet (and especially the web) and with requirements to move
   beyond the restricted subset of ASCII names that have been the

   traditional contents of DNS Class=IN.  This document proposes a
   three-component system for access to DNS names.  In this approach,
   the DNS (more or less as historically implemented) comprises the
   base, with the other two components (or strategies) layered on top of
   it, but not necessarily on each other.  These new approaches involve
   search, rather than the DNS's very restricted lookup (known-item
   search), functions. It also discusses some of the issues and
   challenges in completing the design of, and deploying, such a system.

   These types of services are unnecessary as long as the problem is
   defined as "get non-ASCII identifiers into the DNS, but keep to a
   well-specified set of characters and usage so they retain strict
   identifier properties".  Such approaches do not, as discussed in
   [DNSROLE], solve the problem as perceived by many people. One non-
   technical way of looking at this is that the DNS is fundamentally
   downward-facing: it is designed to support references to network and
   host resources.  Users want something upward-facing, i.e., that
   provides natural-language terminology and searching for resources of
   interest.  And, as the IAB has pointed out [RFC2825], even if "fixing
   the DNS" did the job, it would be the easy part: the harder problem
   is considering and adjusting the applications and applications-level
   user interfaces.

   It has been suggested that introducing a "directory" or "keywords"
   into, or above, the DNS could be used as a solution to the IDN
   problem and, often, several others.  Probing statements about
   "directories" often quickly demonstrates that their advocates don't
   agree on what they mean.  Similarly, many of those who advocate
   "keyword systems" use that term to describe something very different
   from the traditional use of keywords in information retrieval
   systems.  This section outlines a three-strategy search/lookup model
   (adding two location strategies to the one provided by the DNS, i.e.,
   constructing a two or three-layer model, rather than continuing with
   the single one we have today).  These new strategies consist of two
   layers: the current DNS and a collection of alternate methods for
   searching for a network resource, identified by URIs, and using
   different additional information and searching methods. The key one
   of these is a global faceted search-capable component using an
   extremely simple set of facets.  The other proposal is for more
   context-specific or localized, but broader, search approaches. The
   overall document is intended as a strawman for criticism and
   development, rather than as a specific proposal.  I.e., the details,
   especially for localized systems, are left for IETF WG or other

   The document also introduces the concept of an expanded and powerful
   information cache, under user control, which should supercede the
   functions of now-traditional "address books for data", "bookmarks",
   lists of "favorites", and similar methods of retaining an association
   between a user-memorable name and a network resource.  The additional
   power comes from retaining and utilizing, not only the name to
   resource binding, but also information needed to reconstruct a search
   and to determine when to do so.

   As a terminology issue, the "layers" and components described here
   are probably best thought of as elements of the applications layer,
   with actual user-facing applications lying yet above them.  The term
   "search layer" has been used below to refer to both the faceted and

   localized components where it appears to be needed for clarity or
   emphasis.  "Sublayer" and "level" are sometimes used interchangeably
   with terms for those components: suggestions for better terminology
   would be welcomed.

   For the two "above DNS" DNS, international ("universal") character
   sets and scripts are assumed and part of this initial design.  Since
   actual or applications-applied DNS restrictions are not being
   inherited upward into these components, coding can be chosen for
   maximum utility and balance among language groups.  E.g., native UCS-
   4 could be used as an alternative to a secondary encoding form such
   as UTF-8 or an ASCII-compatible ("ACE") recoding such as that
   contemplated by [IDNA].  And, of course, coding systems for
   [ISO10646] characters are required only in on-the-wire transactions
   and operations closely connected to them; we would anticipate that
   localized search operations in areas that use other coded character
   sets might be carried out largely in those locally-chosen coding

   This document is intended to evolve into a framework and model for
   the layered search system, rather than a complete specification or
   even an approximation to one.  It is complemented (for the global
   search system) by [Mealling-SLS], which discusses a CRNP-based [CRNP]
   implementation model for that approach, by the more keyword-focused
   model of [Arrouye], by the caching data provided by Shi and Liu [SHI]
   and, we hope, by other systems more tailored to specific languages or
   cultures.  Additional documents are expected to be developed that
   describe other aspects of all elements of this general proposal.

2  A three (or four) search-layer environment

   The material below suggests three or more components or alternatives
   for name lookup and search:

   (1) The DNS, with the existing lookup mechanisms and a single global
   name space in which names are unique.

     Names are placed in the DNS by those who wish to use those names
     themselves (e.g., for identifying hosts and resources within a
     home, an enterprise, or cooperating groups of organizations).  The
     DNS was never designed for searching for, or querying of, an
     identifier by someone who does not already know what it is.

     A useful analogy has been drawn between DNS names and variable
     names in a programming language [Austein].  Expanding on it,
     locally-memorable, and hence internationalized, identifiers are
     important for network engineers and operators to use in referring
     to resources regardless of whether they are actually valuable for
     end users.  Such engineers and operators are used to developing
     identifiers using highly-restricted character (and other) rules and
     to remembering the identifiers they create (or having other tools
     to deal with them).

   (2) A restricted, facet-based, global search system.

     This system still preserves a global name space, but name strings
     are not expected to be unique and the set of facet values for a

     given entity may not be (see section 3.2).

     Names are placed into this type of system by those who want to be
     found, or want the names or resources to be found, by others.  The
     assumptions are neither that those others will know exactly what
     name they are trying to access (where the DNS requires precise
     knowledge of names or very good guessing) or that names will be
     unique (where the DNS requires uniqueness).  But the search
     activity is still based on names (and attributes), not topics.

     It may be useful to think of this layer as similar to "white pages"
     services.  This comparison is discussed in more detail below.

   (3) Commercial, localized, and potentially topic-specific, search

     These environments utilize multiple, localized, name spaces.  These
     would typically be localized by language or (physical or political)
     geography, but might be structured around, e.g., specific subject

     Names are placed into these systems by those who wish them to be
     found within the specific topic area context (or language or
     locality or combination of them).  Because the environments are
     localized, different search terms and levels of granularity can be
     used in different search sites and name spaces.

     It may be useful to think of this layer as similar to "yellow
     pages" services.  Again, the comparison is discussed in more detail

   (4) Something else?

   As discussed below, it is possible to think about the collection of
   automated content-based search systems that are available on the
   Internet -- e.g., the traditional "search engines" such as [Google] -
   - as components of the "search layer".  The approaches described in
   more detail in this document utilize a "directory" approach, i.e.,
   the information in them is put there precisely because some
   individual or enterprise would like to be found, and found using that
   information.  The search engines, by contrast, rely on analysis of
   the content of online materials to index those materials.

   The following may help illustrate the relationships being proposed

      |               applications                                   |
      |                           |   access cache    |              |
      | . . . . . . . .  . . . .  |-------------------| . . . . . .  |
      |     (directory-based approaches)    | (free-text approaches) |
      | Global faceted   | Topical, usually |       web search       |
      | name search      | local search     |                        |
      |           Domain Name System                                 |
      |  Network resources (by IP Address, Port, etc.)               |


2.1 Base Layer Identifiers -- a lookup system and the DNS.

   In this model, the DNS remains largely as is (see section 3.4ff) or,
   perhaps, a bit closer to its original purpose and assumptions than
   the direction in which it has evolved in recent years.  I.e., it is a
   distributed database, with precise lookups, whose lookup keys are
   identifiers for Internet hosts and other objects.  We give up the
   notion that these identifiers should also serve as human-useful names
   or at least try to abandon that notion.

     As an aside, note that some people have suggested that we should
     dehumanize DNS names entirely, e.g., prohibit the registration and
     use of any name that can be found in any dictionary for any
     language that can be represented in the DNS-acceptable character
     set.  This proposal doesn't include that idea.  But it is absent
     primarily because it does not appear that the transition process
     would be worth the time it would take to explore, rather than
     because it has no appeal.

   The goal for this base component is relatively simple, unique,
   identifiers.  It is probably desirable that these identifiers be able
   to have some human mnemonic value, but less important that they be
   tightly bound to real-world names and descriptions.

   The inputs and outputs at this layer remain as they are in the DNS
   today, although modifications such as those of [IDNA] to accommodate
   non-hostname format names there remain possible if that is deemed
   important for mnemomic or other purposes.  "Hostname-format names"
   are those that are restricted to the ASCII-based "letter-digit-
   hyphen" (LDH) format traditionally used in Internet applications
   [HOSTNAME] and identified as prudent practice in section 2.3.1 of the
   DNS specification [RFC1035]).

2.2 A Globally-accessible Search Component for Names

   A faceted search system with a small number of facets, built on top
   of the DNS.

   Much of the current burden borne by the DNS would appear to be better
   focused on a search system that contains names and a small number of
   attributes represented in name facets.  That DNS burden includes a
   wide range of non-identifier goals and constraints: names that a user
   can understand and find and that have significant mnemonic value,
   names with trademark implications, a wide variety of naming systems
   and, in general, helping people find the things for which they are
   looking.  It is critical that the number of attributes be constrained
   to a minimal set, and that other attributes, especially those of
   special interest, be deferred to the third search layer.

   The term "attribute" is used here and below to identify the
   controlled vocabulary or rule-defined facets as distinct from the
   free-form "name-string".

   It is probably most useful to think about this layer in terms of a
   structured, multifacted, multihierarchical, thesaurus-like database

   with search capability (Cf. ISO IS 5127-1 and IS 5127-6 [THES]),
   rather than as a "directory" in the sense of X.500 and its
   derivatives and antagonists.

2.2.1 The facets

   A key question is what facets to use once the major commercial
   product requirements are removed (to search layer three, see below).
   It appears to me that, to satisfy to the critical name-uniqueness and
   real world pressures on the DNS, candidates for identifying facets
   might be

          Characters from IS 10646, see below.

           Presumably codes as specified in RFC 3066 (see section 3.3.1)

        geographical location
          Country, and/or for some federal countries, country/ province
          ("state"). Granularity is important and there may be a case
          for an additional facet based in a coordinate system or for a
          two-level facet.  See section 3.3.2.

        network location
          If we can figure out what that means and how to express it in
          a canonical way.

        industry category code
          For companies, presumably derived from some existing official
          list such as the WIPO Nice Agreement list [WIPO-NICE]. The
          list would presumably require extension in some way to deal
          with non-commercial organizations and entities and to identify
          resources and services associated with people. See section

   This typology gives the trademark view of the world somewhat more
   precedence in looking at name conflict issues than one might like in
   principle.  But, in practice, one of the key issues we have
   encountered in trying to store "names", rather than identifiers, in
   the DNS is that the process unreasonably flattens the space, not only
   from a technical standpoint but from a usability one.  That "Joe's
   Auto Repair" and "Joe's Pizza" can co-exist in the same geographical
   area without conflict or confusion and that "Joe's Pizza" in one area
   can co-exist with "Joe's Pizza" in another, again without conflict or
   confusion, are the consequence of the way we name and identify things
   in the real world.  Most trademark rules are the consequence of those
   naming systems, not their cause and many perceived conflicts between
   the trademark system and DNS usage are the result of this flattening.

   It is not intended that this level act as a white pages service for
   people.  Doing so leads down several slippery slopes at once,
   including heightened privacy concerns and the associated requirement
   to identify, authenticate, or authorize those submitting queries.

   The general intent is that the list of facets be fixed by protocol
   and that possible values for each facet be controlled vocabularies,

   not necessarily (and probably not) controlled from the same source
   (see section 3.2).  We would hope to utilize existing terminology
   lists where possible.  For a particular record (i.e., a name and its
   set of attributes), and especially if requirements for uniqueness can
   be bypassed or relaxed, the selection (from the controlled
   vocabularies) of particular facet values would be the responsibility
   of the entity registering the names.  In other words, someone
   registering a "name" in this system would select values for each of
   the facets from the controlled vocabulary for that facet as part of
   the process of placing the name into a database.

   It is important to note that the registration of that name would
   include all of the associated facets, although the vocabularies for
   all of the facets other than the "name-string" would be drawn from
   specific, external lists (controlled vocabularies or rules).  It
   would not be desirable, and probably would not be feasible, for
   registrants to record their names in independent, facet-based,
   databases with one facet per database.

   There is also no magic in the proposed system.  Names are placed in
   the system with particular facet sets because a registrant wants them
   there.  A registrant who wishes to have a given name-string
   associated with different facet values (e.g., to identify different
   locations or lines of business) will make multiple registrations.

   While all faceted name strings would contain the same facets, there
   is no technical reason why one or more of these might not have a
   blank (or "missing") value, presumably causing a match to any search
   term for that facet.  More important, searching for a name might omit
   one or more facets from the search, again matching any value that
   actually appeared in the database.

   It should be clear that there is significantly more information (from
   the values of the facets) at this layer than there is in the DNS.

2.2.2  The name string

   The names in this environment can reasonably be written in IS 10646
   codes or some recoding of them.  Since we would be starting more or
   less from scratch, we could select lengths and codings for maximum
   efficiency and utility, not to meet the constraints of existing
   software.  In such a context, this author has a slight bias for
   direct UCS-4 coding.  It may never be clear: the "right" answer lies
   somewhat in the particular application and the eye of the beholder,
   and passions run very high on the subject. This is in preference to
   ASCII-compatible ("ACE") codes; compressed, null-octet-eliminating,
   systems such as UTF-8; or surrogate introducers to hold things to 16
   bits.  The loss in transport efficiency is likely to be more than
   compensated for by gains in cleanliness and equal treatment of all
   scripts.  And, if compression is needed, it is perhaps better to do
   it at the string level rather than the character one.  But that issue
   is separate from the main and important design arguments
   of this document.

   The work done to define "stringprep" [STRINGPREP] and, later, the DNS
   profile in "nameprep" functions [NAMEPREP], developed for IDNA will
   be necessary to determine which names to actually store in the
   database.  But the stakes are lower here than the "get it right or

   fail completely" constraint of the DNS lookup environment: one can
   imagine search mechanisms that would apply a more liberal set of
   matching rules (and/or localized and language-specific ones) than the
   rules used to encode names (much like recent applications protocols
   that explicitly distinguish between the formats one is permitted to
   send and those one is expected to accept (Cf. [RFC2822])).

   At the same time, it would be sensible to permit short phrases as
   these "names", something which is not generally possible in the DNS
   (or in the IDN proposals).  The necessity, in the DNS, to turn, e.g.,
   "Lower Slobbovian University" into "LowerSlobbovianUniversity.edu",
   and then hope case will be preserved (or "lowerslobbovian.edu", or
   worse) is, ultimately, just another example of the unfortunate
   mismatch between the identifiers of the DNS and real-world naming
   systems.  So we would assume that it is a design requirement to make
   it possible to use "Lower Slobbovian University" and "University of
   Lower Slobbovia" as stored names and, if both appear, to treat them
   as approximately equivalent.

2.2.3 Case matching

   In the system proposed here, case-matching should be treated as just
   another case of fuzzy searching and matching, not a relationship with
   unique status.  As discussed below, in all cases, the user (or her
   agent) would provide a string, some subset of facets, and search-
   method specifications as input, and would receive a set of matching
   results, in the form in which they are stored in the database.

   Case matching -- treating upper and lower case letters as identical -
   - is another historical DNS property that does not have a simple and
   unambiguous interpretation in the real world of non-ASCII character
   sets and a range of language applications.  Some scripts contain
   glyph forms that clearly represent two cases, some scripts clearly do
   not have case distinctions, and, as the IDN WG has discovered, there
   are character-matching requirements in some languages (e.g., equality
   of simplified and traditional Chinese (e.g., see the work now going
   on to handle preferred forms and variants for those character [JET-
   Guideline], and below) for which the appropriateness of an analogy to
   case-matching has caused a considerable controversy, not least
   because of the apparent absence of a set of mapping tables that cover
   all of the possible character pairs.  Even in scripts with clear case
   distinctions, it is common to find lower-case characters with no
   corresponding upper-case one (e.g., the German Eszet) or no upper-
   case character that maps uniquely to a lower case one (e.g., "A" in
   French may maps to either "a" and "a with accent").  The IDN WG, and
   others who have examined the cases closely, have also discovered
   that, even for scripts with the presence of clear case distinctions,
   the matching rules sometimes differ by geographical locality.

   It is not completely clear how case matching should best be handled.
   It does appear almost obvious at this time that the model the IDN
   group created with IDNA is not desirable.  That model essentially
   results in different rules being applied to different scripts: case
   matching in some situations, none in others, and some but not all
   characters in yet other cases.  It may be the best compromise given
   the combination of the constraints of the DNS with the idiosyncracies
   of Unicode, but, with or without the DNS constraints, we should
   strive to treat all languages and scripts in as nearly an identical,

   or at least non-discriminatory, way as possible.

   While there are other options, it would appear to be better to handle
   case-matching on the server, as it is done in the DNS.  As with other
   searching variants, it should be possible to return the form of the
   name as stored in the database while finding it using any of the
   user-acceptable variations (use of client-side string preparation for
   both the stored name and query formation, as a DNS internationalized
   on the IDNA model seems to require, loses information that some
   people consider important).  Case-matching in the proposed faceted
   system could be applied (or not) as dictated either by a heuristic
   using the combination of the language facet and a query containing
   the preferred location-context of the user (see below).  Or there
   could be an explicit query flag (or indicator carrying more than one
   bit of information).  This author tends to prefer the latter because
   of a profound distrust of heuristics, but the question requires
   additional study.

2.2.4 More complex character matching

   The case-matching strategy applies to more complex cases of character
   matching as well.  If one can establish sufficient context, and
   specify the types of expanded matching to be used, and permit
   multiple variants to be returned to the application, then one could
   support matching of similar-appearing characters (e.g., Latin "A" and
   Greek Alpha), or Latin-derived and Cyrillic-derived scripts for
   Serbo-Croatian, or, perhaps most important, mapping between
   Traditional and Simplified Chinese (see section 3.6.3).

2.2.5 Query formation and specification

   As is common with systems of this type, we would anticipate the
   possibility of searching on any of the attributes and that searching
   on free-text strings would not be exact (i.e., near-match responses
   could be returned using any of several algorithms, with the user
   making choices).  One could also imagine distance function
   calculations on appropriately structured restricted-vocabulary facets
   being implemented in some search engines.  As is equally common, we
   should think about user interfaces that store both queries and
   response sets so that the responses could be used offline and
   refreshed when the client systems were attached to the Internet (see
   the discussion of caching in section 3.6.2).

   At the same time, we would assume that a search without at least some
   approximation to a name string would rarely be productive and would
   expect search systems to be optimized accordingly.

   In summary, the goal at this layer is to provide tuples of human-
   recognizable (not just mnemonic) facets (names and attributes), but
   names that are relevant within the context set by the attributes,
   rather than a global system based on the names alone.

   The input at this layer is a query consisting of search values for
   one or more of the facets, plus information to control the search.
   E.g., to the extent that designers of search protocols can provide
   the proper tools and terminology, one would expect the query to be
   accompanied by rule statements about how much "fuzziness" was
   permitted, how "distant" names might be from the chosen ones and

   still be selected, whether character set or language translation (or
   even phonetic recognition) was to be applied (and whether translation
   was to be restricted to a small group of languages or made more
   general) and so forth.

   The outputs are still being discussed, but would appear to best be
   the full facet set of the matched tuple(s) (more than one such set if
   multiple tuples match) and one or more URIs [RFC-URI] associated with
   each tuple. These URIs, and the DNS entries which they contain and to
   which they refer, will generally have the same uniqueness properties
   of the DNS itself: while a query, or full set of matching facets,
   could match (and return) multiple DNS names, nothing would make the
   DNS names less unique than they are today (i.e., as the DNS

   An alternative to using URIs as the return information is to simply
   return fully-qualified DNS names, leaving ancillary information about
   location of particular information and the protocols to be used with
   them, outside the scope of this system.  The author reluctantly
   abandoned that approach as it became increasingly clear in
   discussions that the additional information was necessary: users will
   search for information, or a resource and the mechanisms for using
   it, and are little-interested in what the network might, or might
   not, consider as a resource.  Even if URIs are returned, one of many
   interesting questions appeared to be whether these search systems
   should pass through and return the DNS records themselves (labels,
   class, type, and target) or whether they should return names (labels)
   and let the applications do the DNS lookups.  The latter now appears
   obvious, not only because it can be anticipated that some URIs will
   not directly utilize DNS names, but because the data expiration
   properties of DNS resource records may be very different from that of
   a data reference or search result that can point to and rely on the
   DNS name.  The substitution of URIs for DNS names does, however,
   increase complexity and the risk of recursion problems, and that
   tradeoff should be understood and appreciated.

   For the cases in which DNS-level information is the required
   response, a URI type might be created for that information and used
   to abstract the return information into something applications can
   then specify or decode as appropriate.  As suggested above, use of
   such a URI would need to be carefully structured to avoid complex
   problems (e.g., recursion in either this system, the DNS, or both),
   but might be a reasonable approach.

   Regardless of whether the output is a URI or a DNS name, DNS
   extensions such as IDNA will presumably be applied to them.  I.e.,
   the process of looking up DNS names that emerge from the these search
   components would presumably go through the extended process specified
   in IDNA or its descendants.

   Experience with the DNS and other distributed databases also argues
   persuasively that these records are not forever.  Unless there are no
   local copying and caching mechanisms (which seems unlikely and hard
   to enforce), some type of time to live (TTL) or other expiration or
   reverification mechanism will be needed.

2.2.6 Imprecise matching

   <<to be supplied - see "placeholders" at the end of the document>>

2.2.7 Registration rules and query rules

   As with the DNS, it may be more important to be conservative about
   what types of names are registered than to be restrictive about
   queries.  At the same time, if there are well-known and easy to
   understand rules about registration restrictions (probaby implying
   that the same registration rules must be used globally), it should be
   possible to optimize query interfaces (corresponding to "resolvers"
   in traditional DNS terminology) to immediately return "invalid name"
   error messages rather than returning "not found" after a search.

   One could, for example, easily imagine a query interface that would
   maintain a local (although periodically updated) table of ISO 3166-2
   codes to perform validation against the major components of
   geographic names before initiating a search of a remote database.

   Similarly, if a sublayer two database was created for a particular
   country and language, registrations in it would presumably be
   restricted to records for that country and language, and to name
   strings that conformed to validation rules developed for that country
   and language.

   The category lists (restricted vocabularies) for each of the facets
   would presumably come from different, although standardized,
   databases, e.g., IS 3166-2 and UN/LOCODE for geographical
   information, RFC 3066 for language names [LangTag], an extended
   version of the WIPO-NICE code set for industry codes.  But the name
   databases themselves would contain a complete set of tuples for the
   facets (some, of course, might be missing or, more precisely, "let
   anything match").

2.2.8 Server location

   The DNS avoids the problem of server location through its strict
   hierarchy model: hosts are preconfigured with hints as to how to find
   the root servers, and all other servers are found via delegation
   records.  Since this model contemplates relatively independent sets
   of servers for individual records, under separate administration, the
   convenience of the DNS model is not available.  Instead, some
   mechanism for server location is needed.  At least the following
   models seem plausible:

   (i) A common directory of servers, perhaps stored as bootstrap
   records in the DNS.  The advantage of this approach is that it
   appears, on first glance, to be easy and obvious.  Its disadvantages
   include an implicit requirement for agreement on how servers for
   selected and the list administered.  Also, information about
   prioritization of servers and server search would need to be provided
   out of band in some way.

   (ii) Each user would need to preconfigure a server, or have that
   information in a client default.  That server would be responsible
   for determining which servers were to be searched if it did not have
   the needed records available, those would specify further servers,
   and so on.  This approach would be straightforward and would solve
   the problem of prioritization.  However, especially for searches for

   web resources, it would tend to automatically give the suppliers of
   dominant browsers control of server resources and search choices.

   (iii) Some more automated, "rootless", procedure for service location
   might be used, as in [Mealling-SLS].  Such an approach holds
   significant promise, but has never been attempted at full Internet

2.3 The Third Component: Locality and/or content-domain-specific data
    and mechanisms.

   The problem with the faceted global search model is that there are a
   number of usability and marketplace pressures for naming systems that
   offer finer granularity and a better match for user needs.  For many
   purposes, users want localized, not global, systems. This has been
   confirmed in those systems which have been included in experiments or
   partially deployed (see, e.g., [RFC2345] and [RealNames]), which
   require contextual localization, not a single global environment.
   There are many causes for this, but requirements for very specific
   searches that are geographic-area, topic-area, or language or
   culturally specific, tend to dominate the list.

   The issue is perhaps illustrated by an example.  Suppose the
   granularity of an entry in a faceted system is

     {"Joe's", "UK", Restaurant,... }

   Now, one might want to create a business around a restaurant
   directory for Bristol.  The developers would probably want to
   construct a database that contained exact locations, type of food,
   menu information, prices, etc., and permit people to query it that
   way.  That type of product bears a strong relationship to traditional
   yellow pages services: the best attributes to collect and the optimal
   way to organize them will differ by topic (e.g., for most people,
   "menu" has no obvious analogy in an automobile repair shop) and the
   business models are fairly established.  Part of the history of those
   business models is the observation that, when there are competing
   yellow pages services (or guidebooks, or other, similar services),
   those who consistently make better (and "more accurate") choices of
   categories and keywords tend, other things being equal, to be judged
   "better" and to capture larger market share.

   A related restaurant example may illustrate another important issue:
   if one looks for Chinese food in Phoenix, the search key "Chinese
   restaurant" may be appropriate and adequate: there are few of them,
   and they are not highly differentiated.   In Washington, DC, enough
   restaurants specializing in Chinese regional cuisines are now
   operating that more precise categorization is needed.  And, in
   Shanghai or Beijing, "Chinese restaurant" is presumably not a useful
   category at all: regional or other cooking styles would be key to
   finding something useful, rather than obtaining an extremely low-
   precision result.

   One can imagine many different types of keyword and (yellow pages-
   like) directory services of this general character, using different
   types of protocol mechanisms as well as different types of database
   content and schema.  But those services are nearly ideal candidates
   for competition: there is no requirement that either the providers or

   the services be global or unique or even highly standardized.  Having
   all three search layers bound to the same data sources --inheriting
   values from them if one wants to think about it that way-- would
   provide a degree of consistency that might be very attractive to
   users, so there are clearly issues here that will need to be worked
   out in the marketplace.

   Directories of these types are, of course, common and widespread
   outside the Internet.  There is no shortage --some would say there is
   a surplus-- of directories and guides to resources and services of
   particular types and in particular areas.  Advertising or placement
   fees from resource owners support some of them. Others are supported
   by book sales or fees charged to users, and still others by a
   combination of approaches.  Most of these directories and guides
   publish year after year and seem profitable.

   Inputs for these locally-based systems will differ by service: one
   can imagine free-text interfaces and menus (but see section 2.4) as
   well as systems that more closely resemble faceted search terms.

   Outputs will normally be globally-valid names: URIs, DNS names, or
   sets of facets for the global search system.  However, since users
   are unlikely to distinguish between global, faceted, systems and
   these local ones (or even between them and the DNS or other search
   mechanisms), it is important that these queries and results be
   locally cacheable on the same basis as global queries and results
   to preserve name and reference portability.

   Summary: Just as the monohierarchical identifier-lookup system at the
   basic DNS level should be supplemented by a multilingual,
   multifaceted, multihierarchy search system on a global basis, that
   global system should be supplemented by a collection of localized,
   subject- and topic- specific systems.  These localized systems need
   not be centrally coordinated in any way, although enough similarity
   of function and interface to permit a common local caching
   environment would almost certainly make them more consistent for
   users and easier to market.

2.4 The Non-directory Search Component: free-text searching

   The approaches described above omit one set of techniques used today:
   "web searches" on full text or its equivalent.  These systems have an
   important role (and, similar to the localized and topical searches
   described here, there seems no particular advantage to trying to
   standardize them worldwide).  But their disadvantage, if seen as a
   DNS surrogate or replacement, is that they have difficulty
   distinguishing between the name of something, a pointer to it, and a
   reference to, or discussion of, it or how it works.  The other
   systems discussed in this document are all "directories" in the sense
   that someone must make an explicit decision to put an entry in a
   database; they are not full text searching systems or analogues of

   If, for example, one is looking for a web site for a company, a
   search of the local "yellow pages" would presumably find that site
   (assuming the company wanted to be found).  Global faceted search (or
   even the DNS) might find it with some guessing, but this fourth level

   would (as web search engines do today) probably not reliably
   distinguish the company's site from sites that reference the company
   or its products.

   Locally-specialized search produces information that is explicitly
   bound to the query, i.e., what one is looking for, while a search
   engine returns values that also include sites where the subject of
   the query might have been mentioned.

2.5 Database and searching differentiation

   In both of the directory-based search components, but especially for
   global faceted search, we assume that "compiling databases" (i.e.,
   registry and, if appropriate, registrar functions) and "designing and
   building search functions and providing search services" are
   separate.  It would be necessary to have database interfaces be
   sufficiently general and well-specified that referrals were possible
   and different search services could rest on top of them, but we would
   expect some search services to be much more extensive than others and
   for their vendors to seek increased compensation for those more
   extensive servces.  In many cases, the market would eventually sort
   out the optimal combinations of capabilities and costs.

   Ultimately, the term "fuzzy search", used extensively in this
   document and elsewhere, is handwaving.  Whether heuristic or
   deterministic, one must devise, for each facet, systems for
   determining whether matches have occurred and, for inexact matches,
   whether the combination of query term and database entity are "close
   enough" together to be candidates for being returned as responses.
   We can imagine phonetic matching as well as character-string
   matching, application of contextual rules as well as simple
   character-pair rules for matching of Traditional and Simplified
   Chinese, and similar rules for matching of Kanji and kana strings.
   And we would presume that users, or their agents, would be able to
   control such decisions by choice of search providers, configuration,
   or choices on a per-search basis.

3  Context and Model Details: Global faceted search

3.1 The data search and access model

   It is interesting that recent IETF "directory" work has focused on
   accessing mechanisms without worrying intensely about the underlying
   database content, maintenance, and update issues.  Those latter
   issues seem to be the harder ones, i.e., the difference between LDAP
   [LDAP] and CNRP [CNRP] may make less difference than how we
   structure, maintain, match, and distribute the relevant data.

   Of course, that does not suggest that work on accessing mechanisms is
   not important or that it isn't required.  And, to deploy the model
   suggested above, we will need to deal with a pair of uncomfortable

        * CNRP looks interesting, but has not been widely implemented or
   deployed in production.

        * LDAP is widely deployed, but primarily in implementations that
   contain sufficient extensions and special features to be non-

   interoperable. Effective referral mechanisms have also not be clearly
   standardized in LDAP, and this might provide a barrier.

   Some readers of earlier drafts have also suggested that the history
   of LDAP points to local extensions that will result in inconsistent
   search behavior, while CNRP may be better specified (or at least
   closer to a clean slate).

   If we are going to choose -- and global faceted search certainly
   implies a choice -- we need to figure out how to do that.

3.2 Uniqueness of name structures in global faceted search

   There are cases to be made both for and against uniqueness of names
   (more precisely, of the combination of the name-string facet and all
   of the other facets) at this sublayer, and even a partial middle
   ground, in which names are unique within a registry namespace, but
   there are mechanisms for identifying such spaces so that the names
   are unique across the Internet.  The community should address the
   tradeoffs because no position is ideal; summaries of the extreme
   positions are below.  In none of these cases is it necessary, or even
   desirable, that the name-string itself (without the additional
   "attribute" facet values) be unique.

3.2.1 The case for unique names

   The IAB's discussion of DNS root uniqueness [RFC2826] argues that DNS
   names must be unique, i.e., that there must not be alternate or
   surrogate root structures if the Internet is to survive as a seamless
   whole and be universally addressable and accessible.  Even with
   imprecise matching, similar arguments may apply at level two,
   especially if this is the first level at which names in natural
   languages (hence including "multilingual" names), rather than
   constrained identifiers, appear.  The mathematical arguments aside,
   the main argument for uniqueness is that a given combination of name-
   string and facets will yield exactly one logical host (or equivalent,
   an approach called "direct navigation" in some of the so-called
   keyword proposals [Arrouye]).  If this is not the case, it seems
   inevitable that users will be faced with choices they need to resolve
   even when they have an exact match for a full set of facets.

   Users clearly prefer such approaches.  The often-cited user ideal is
   to be able to enter a very short and simple string and have exactly
   the desired resource appear, more or less on a "do (or find) what I
   mean" basis.  Unfortunately, reality has a tendency to intrude on
   such systems, as discussed below and in [DNSROLE].

   Because the name structures stored in the databases of a global
   system (faceted or otherwise), in this case, still must be unique,
   some mechanism for registries or structuring of names will be
   necessary to avoid conflicts.  The problem is somewhat easier than
   the ones encountered by ICANN and its associated groups because the
   very structuring of the names and attributes creates opportunities
   for dividing up responsibilities, but the registration problems exist
   nonetheless and will need to be resolved.

3.2.2 Non-unique names

   Conversely, one could have multiple appearances of the same set of
   facets (including the name-string), such that an exact match could
   still yield multiple "hits".  This would have the advantage of
   eliminating all requirements for monopoly registries or [other]
   technical mechanisms for guaranteeing that name conflicts did not
   occur.  The disadvantage is that it would force more user choices or
   heuristics, and at least some errors in which the wrong host or site
   was identified would be almost inevitable.  Issues of non-uniqueness,
   and having to seek additional information to differentiate among
   choices, are typical in normal life (see the discussion of "caching",
   below); it is unlikely that we can make the Internet different.

   As extensive use of intelligent per-user (or per-group) local caches
   or directories ("bookmarks", "favorites", etc.) evolve, which we
   consider almost certain, they might also make the difficulties with
   non-uniqueness insignificant.  This would be especially likely if
   these directories contained not only a keyword and (DNS name or URI)
   target, but also a stored form of the search used so that local data
   could be recalculated and replenished.  See section 3.5 and 3.6 for
   some related discussion.

3.2.3 A middle ground approach: artificial uniqueness

   A proposal was made in the initial version of [Mealling-SLS], that an
   additional facet could be added to represent the registry which
   records the names.  If this were done, names could be kept unique
   within registries and would be globally unique as long as the
   registry-identifying facet had a unique value for each registry.
   There would be no need to restrict the number of registries in this
   model or resolve naming disputes among them -- each one could have a
   unique, randomly-generated and assigned identifier-- so the approach
   could provide some degree of technical uniqueness while still
   preserving most of the benefits of the non-unique approach.

   That model could, of course, be deployed at a "registrar" level
   instead, just by changing the assignment of the identifier facet from
   value-per-registry to value-per-registrar.  Other variations are, of
   course, possible.

   Whether it is desirable or not is an open question, since it
   inherently turns each registry (or registrar) into an arbiter of
   priorities or rights to names, or requires that some outside agency
   perform that function.  There seem to be strong arguments for
   avoiding those alternatives.

3.3 Sources for controlled-vocabulary facets ("attributes")

   We anticipate that most of the sublayer two facets other than the
   name-string itself will have values chosen from controlled
   vocabularies I.e., the user-registrants will be able to select
   whatever values seem to match their needs, but only from pre-defined
   lists of possible values.  These are not intended as free-text
   entities; to make them free text would push the second-sublayer
   system toward the lowered precision of Internet search engines and
   other free-text search environments.  The facet values that are not
   populated from controlled vocabularies will be determined by
   deterministic and unambiguous rules.  For example if one of these

   attributes is a geographic location that uses a coordiate scheme, the
   definition of the coordinate scheme should be sufficient to yield a
   predicatable and exact value.

   The question, then, is how to establish the vocabulary lists and
   write the definining rules.

   It has been something of an Internet tradition, building on Jon
   Postel's principles for registration and registries, to try to avoid
   having IETF or IANA become embroiled in controversies about names,
   their ownership, propriety of using them, and so on.  The use of IS
   3166-1 alpha-2 codes as the basis for "country code" top-level domain
   names (see [RFC1591]) is just one instance of the application of this
   principle.  Following this tradition, facets should be chosen, in
   part, on the basis of availability of pre-existing, well-known lists
   of names and authorities or, at worst, the ability to identify
   relatively non-controversial authorities who can quickly establish
   such lists.

   Some specific possibilities are discussed in the subsections that

3.3.1 Discussion of language identification

   The IETF already has a standard for identifying languages and
   dialects, documented in [LangTag] and based on an ISO Standard
   [ISO639].  It appears that it would be usable here, with minimum
   fuzziness associated with an exact match of all subtags and a higher
   degree of fuzziness permitting matching different (national or
   dialect) variations on the same language.

3.3.2 Discussion of geographical identification

   For larger countries, and areas with many semi-independent
   administrative districts, identification of the country may not
   provide sufficiently precise resolution.  On the other hand, it is
   desirable to have a scheme that is hierarchical or that otherwise
   readily permits search expansion.  Conceptually, the coding should be
   something like

    country / administrative-district / city or town

   Fortunately, such a system exists as a generalization of one that is
   in common use in the Internet.  ISO 3166-2 [ISO3166] provides a
   model, and list of values, for representing countries and
   administrative districts, and is designed to be compatible with the
   UN/LOCODE list when those further subdivisions are provided and
   satisfactory from a national point of view.  Since ISO 3166 is
   probably even more satisfactory for this purpose than it is for its
   use in defining ccTLD names, it should probably be used (with the
   UN/LOCODE where appropriate) unless something clearly better can be
   found.  For example, a complete coding using this approach would be
   something like "DE-BW-DESTR" for Stuttgart.

   The corresponding matching rules seem obvious, but, to review them:

   * If the stored record contains all three elements, then a query of
   (and fuzziness=exact) should imply that

     "country" matches everything "country and subdivision" matches all
     cities in that subdivision, but does not match other subdivisions
     "country, subdivision, city" matches only that exact stored record.

   The "fuzziness" indicator should be fairly clear here, e.g., 0=exact,
   10=match next level ("country, subdivision, city" matches the whole
   subdivision), 99=all levels ("country, subdivision, city" matches the
   whole country), and intermediate values might match adjacent cities
   or subdivisions using some reasonable distance or adjacency function.

3.3.3 Discussion of Industry Types

   The WIPO codes, discussed above, are suitable for companies and
   industries of the types that normally use the trademark system.  They
   are not a good model for identifying individuals, nor are they
   suitable for most non-profit organizations, governments, and NGOs.
   The facet described as "industry type" here will need to be organized
   so as to identify and accommodate separate classification systems for
   different types of entities.

3.4 Deployment against the existing DNS base

   As with the "new class" approach to DNS changes [NEWCLASS], the
   approach outlined here does not require any changes to the existing
   installed DNS base.  But, like all solutions to the multilingual name
   issues, it requires changes to all relevant applications.  The notion
   of moving from lookup to searching does imply that we will need not
   merely to change the code that calls the name resolution system, but
   also to rethink the UIs of those applications.

3.5 Thoughts about user interfaces (UIs)

   There are many possible models for user interfaces to be used with a
   system of the type proposed here.  The IETF should, as usual, remain
   agnostic about them.  At the same time, some notions about possible
   user interfaces are important to demonstrate that the concepts are
   practical and to inform the design of protocol interfaces.  So, with
   the understanding that other approaches are possible, and may be

   As discussions on both DNS "searching" and under the somewhat
   misnamed topic of "multilingual names", and the general model
   presented here, have evolved, it has become apparent to some
   observers that these approaches would be best realized in conjunction
   with user-specific directories or memory with refresh capability,
   whether modeled on a local directory, or cache, or history file, or
   something else.  It has been surmised [WJR ref?]  that the behavior
   of typical users is to spend most of their time using or referencing
   known services and hosts (whether web sites, hosts used in email
   addresses, or other services) and much less time "searching" for
   unknown resources.  If this is actually the case, then a typical
   reference should involve a DNS "name to address" lookup only, even
   though it would be desirable for the DNS name to not be visible to
   that user.  The user might reasonably see his or her original
   collection of search terms, or a name assigned to that search or its
   results, but actual searching would take place only as a first-time

   activity or in the process or refreshing the search and results (at
   user request or, perhaps, automatically).  An approach for handling
   these issues appears in section 3.6.2.

3.6 Implementation models

   While this document is not an implementation specification, nor is it
   intended to substitute for one, some remarks about implementation
   issues may be helpful in understanding the concepts that appear

3.6.1 Calling and returning values

   While it is not the only way to do it -- and others may be more
   efficient -- it is useful for this section to consider the database
   associated with a given server/provider as consisting of a collection
   of records, each of which consists of a key tuple consisting of one
   value for each of the facets, a URI, a text field of supplemental (or
   "comment") information, and an expiration date and/or TTL.

   The textual field is expected to be useful to the user (or an agent
   acting for her) in differentiating between URIs or other target
   information.  Some structuring of it, and/or tagging of the
   information it contains, would probably be desirable, as would some
   upper bound on length.  A potentially long and highly structured
   logical content for this field could be provided by the use of a
   reference via a URI, or the primary URI could provide a pointer to
   such information that indirects to the actual content being sought.

   A query to the server consists of a set of (facet, fuzziness
   indicator) pairs, one pair for each defined facet.  A null value is
   defined for each facet; use of that value implies that any value for
   that facet in the database would be considered as matching,
   regardless of the fuzziness indicator value.  A given server may
   choose to reject a query that specifies null values for one or more

   Unless all values for the permitted level of fuzziness are set to
   disable fuzzy searching and matching, the list of facet values in the
   query need not correspond exactly to any record in the database for
   records to be successfully returned.

   The server can then return:

      * A "not found" response, indicating that no records were found
      that matched the facets within the specified fuzziness criteria.

      * A response that the query is not acceptable, e.g., because of
      null values for specific facets.  This response would indicate the
      facet(s) impacted.

      * A normal reply.  That reply would contain one or more records,
      each consisting of

            The facet values as stored in the database

            The URI as stored in the database

            The textual comment value, if any

            A TTL for the response.

      This provides information about what was actually matched,
      suitable for caching and repeating of the query as needed as well
      as user selection from the records and/or immediate use of the

3.6.2 The cache model

      The model proposed here is ultimately one of "searching" --
      finding a resource in a way that may involve some interaction
      between the various databases and the user.  It differs from the
      "search engine" approach because the databases are intentionally
      populated (not unlike the DNS, although syntax and semantics are
      different) and the searches are highly structured.  With the
      "search engines", the databases are largely populated by automated
      processes that walk through the Internet (or the web) picking up
      data of possible interest.  And the queries use, at most, boolean
      conditions, not a structured, faceted, architecture.  The obvious
      advantage of a search technique of this sort is that it should
      have good odds of permitting owners or operators of resources who
      wish those resources to be found to have them efficiently found by
      those who are looking for them.  But it is unlikely that the
      process can be made as fast or resource-minimizing as a DNS lookup
      where the fully-qualified domain name is already known.

      At the same time, the nature of the systems being proposed makes
      it likely that a user will think of a particular resource (or its
      location) in terms of the terminology used to find it.  And,
      especially if the user needs to be involved in the search and
      resolution process to identify a resource (or resources) of
      interest from among those that match a set of facets, users will
      not tolerate having to go through the process on every reference.
      The combination of these factors makes it almost essential that it
      be possible to maintain a local table of references and targets
      (in DNS or URI terms) so that additional references soon after the
      first can be used by protocols to directly access recently-used
      targets without having to go through the search and resolution
      process each time.

      The process of locating telephone numbers may constitute a useful
      analogy here.  Few would find it conceivable to approach the
      telephone system the way the DNS is often approached: to start
      guessing and dialing numbers, without prior hints, as the way to
      find the correct number for a particular enterprise or individual.
      Instead, people use a number of resources that lie outside the
      telephone number system itself to locate a number.  These
      resources might include:

         * White pages directories.  These support fairly exact search,
         but with some cross-references, added semantics or qualifiers,
         and the ability to take advantage of being able to see adjacent

         * Calling a telephone operator and asking.  This is typically
         an indirect method of conducting a white pages search, but may
         involve additional mechanisms.

         * Yellow pages directories.  These are organized by topic, with
         the topics varying by locality.  One first finds the relevant
         topic, then the entity of interest.

         * Other sources, such as advertisements, articles, or

         * The "ask a friend" technique: find someone who knows the
         relevant number and ask.

      In each case, most users will find a way to remember the number if
      it will be used again.  They are entered into personal address
      books, recorded in intelligent telephones, or remembered in
      "recently called" lists.  These mechanisms are similar to the
      "cache" being posited here.  And it should be noted that the
      mechanisms used are quite similar to those typically used for
      email addresses.  "Guessing" may be appropriate for a number or
      email address that is already known, at least to some degree of
      certainty, but is not generally workable if the target value is

      Even "soon" may be quite different from our experience with the
      DNS.  With the DNS, the resources bound to names are typically IP
      addresses or something similar, and these change frequently
      enough, often on short notice, that "time to live" (TTL) values
      are typically short, rarely more than a day.  By contrast, the
      faceted name resulting from a global search, or the information
      from a localized one, are likely to represent a fairly long-lived
      relationship with the DNS names and URLs that they identify.
      Clearly, it should be convenient for the user to reinitiate the
      search when that is obviously needed (e.g., if a target goes bad)
      but TTLs for ordinary refreshing of a search will, in most cases,
      be set closer to the order of weeks than to minutes or hours, with
      the DNS taking responsibility for the volatile portion of the
      references, as it does today.

      A facility similar to this is provided for web browsers by the
      common "bookmarks" or "favorites" functions, but those support
      only a mapping between a user-specified name and a URI.  If the
      URI goes bad, or the information used to determine it becomes
      obsolete, there is no mechanism for repeating the search other
      than the user's memory of what the name might have meant.  Caching
      operations powerful enough to prevent unnecessary searches or user
      intervention in this environment require much greater

      The facility needed here (extended "bookmarks" or "favorites" if
      it is useful to think of them that way) can be thought of as a
      local cache of queries and responses with sufficient information
      to both immediately locate a target associated with the user's
      perception of what was looked for and of "refreshing" the search
      if circumstances changed or values timed out.  The idea of a
      "search" here should be very general, and might even extend to a

      reference such as "I asked my friend the following question" (we
      would not expect references of that type to be automatically
      repeated, but the source information is useful).  In the presence
      of a particular query, a client system would presumably check for
      a matching cache entry.  If one was not found, the specified
      search would be performed, yielding values that might require user
      intervention for selection.  Once selected, the search, the full
      set of facets returned, the URIs, and any TTL information would be
      stored (possibly using a user-supplied name or tag) and the
      resource accessed via the appropriate DNS name or URI.  If the
      search or tag was found in the cache, checks would be made for the
      values being current and then the DNS name or URI used directly,
      without going back through the search procedure.

      One useful consequence of this is that the number of queries to
      the database will be roughly proportionate to the number of new
      inquiries by the user (increased by the impact of TTL timeout and
      user-initiated repeated search).  That number should be much
      smaller, and hence imply significantly less load, than per-
      reference DNS queries.

3.6.3 An example: Looking at Chinese Traditional-Simplified Mappings

      One of the problems that the IDN WG has been unable to solve in a
      satisfactory way is the requirement that strings written with
      Traditional Chinese ("TC") characters match those written with the
      corresponding Simplified Chinese ("SC") ones.  The relationships
      among these characters have been variously described as similar to
      font differences that are not properly reflected in the IS 10646
      coding and structure and as similar to case mapping in alphabetic
      scripts that support case.  Although both are thought-provoking,
      there are significant weaknesses in both analogies.  But the
      problem is sufficiently important that the working group has
      received requests to delay DNS-level internationalization
      implementation of all (or selected subsets of) Chinese characters.

      Fortunately, mapping between TC and SC is fairly easily handled at
      sublayer two of the system proposed here.  Details and variations
      still need to be worked out and a specific proposal chosen and
      refinded, but it appears that something similar to the following
      outline would be one option:

      Unlike the DNS, the sublayer two system will have the critical
      language identification information available.  This eliminates
      the problems associated with distinguishing Chinese character
      usage from uses of similar characters (at the same IS10646 code
      points) in Japanese and Korean.  Assuming that the language is
      Chinese, "fuzziness" could be used to determine the precision of
      matching required.  E.g., "no fuzziness" might be construed as
      "exact match", i.e., no attempt at TC-SC matching.  A low (but
      non-zero) fuzziness value might permit unambiguous single-
      character (i.e., "one to one") matching between TC and SC
      characters, but no other variations.  And a higher degree of
      fuzziness might match more extensively, including cases in
      multiple characters of context or user selection from a menu or
      pick list were needed to determine a correct match.  <<>>Is
      distinguishing between these two cases actually helpful?  I would
      think it would be useful in the design of good-quality user


      If it were worthwhile, other variations on a sublayer two system
      could be used to handle different character input models as server
      functions.  For example, use of a different language subtype (or a
      heuristic on the name string) could permit phonetic input
      (presumably Pinyin, but, if anyone wanted it, a different subtype
      could permit use of alternate systems such as Wade-Giles) even
      though the names in the database were stored in Chinese
      characters.  Use of phonetic input of course absolutely requires
      matching of TC and SC characters.

      An interesting approach, using language-specific variant tables,
      appears in [JET-Guideline].   That approach is designed to work in
      conjunction with IDNA and involves client-based variant tables.
      With obvious modifications to bring the tables onto the server and
      to treat some of the variants as different degrees of
      approximations, it might be even more effective in the environment
      proposed here.

3.6.4 An example: Distance functions and Latin-based alphabets

      The discussions of case mapping for scripts in which the rules are
      subtle or culturally dependent has restarted the argument in some
      quarters as to whether the case-mapping rule of the DNS was wise.
      The alternate position is that users are better off with a single
      form of writing an identifier and that they will then "get used to
      getting it right".  The use of fuzziness with such scripts might
      permit this issue to be left to the user or interface designer,
      e.g., no fuzziness would imply no case matching, somewhat more
      fuzziness would permit case matching in those cases where the
      rules were exact and one-to-one, and additional fuzziness would
      permit matching, e.g., with and without diacritical marks or
      across character variants.  The presence of language information
      makes these approaches much more workable than they would be with
      the DNS, even with a more complex canonicalization process than is
      now anticipated in "nameprep".

3.7 Older applications

      To fully realize the benefits of internationalized naming requires
      changing all relevant applications to understand the new method,
      whatever it is.  Even the "internationalize the DNS" proposals are
      subject to this principle.  Older applications will see distorted
      and unfriendly names under some systems, and no names at all under
      others (some approaches might cause implementations of some
      applications to fail entirely).

      The environment contemplated here is a "no international names in
      old applications", i.e., "no new names without upgrading", one --
      applications that have not been upgraded will not see
      internationalized names or other natural-language phrases, nor
      coded surrogates for them.

      The advantages of a "no names without upgrading" approach are that
      it avoids confusion and the risk, however slight, of catastrophe.
      As with the original host table to DNS conversion, they provide an

      incentive to convert old applications to make newer naming styles,
      and newer names, visible.  None of these transitions are ever
      easy, but it may be worth going through this one to get things
      right, rather than investing a large fraction of the pain to get a
      solution that doesn't quite do the job.

4  Context and model details: Localized and Topical Searching

      <<to be supplied>>

5  Comparisons to existing and proposed technology

5.1 The IDN Strawman

      After the IETF IDN working group came into being, it rapidly
      excluded all models not based on the assumption that
      internationalized name referencing issues and requirements --
      including the requirements, not heretofore satified even for
      ASCII-based names, to be able to search for things using the DNS--
      could be achieved by placing non-ASCII identifiers into the DNS
      itself, in some coded form.  These identifiers were commonly
      described as "multilingual names".  That terminology further
      complicated the work program and consensus-seeking process in that
      working group.

      Many of the problems associated with trying to overload the DNS in
      this way have been described in [DNSROLE].  That document, and the
      experience from which it is drawn, predict that the products of
      the IDN WG effort, specifically the IDNA standard, will ultimately
      fail if they are evaluated in the context of applications that
      require sensitivity to the characteristics of particular
      languages, rather than just an expanded set of characters to be
      used in identifiers.  As implied in the [DNSROLE] document,
      consideration of language-related issues and their appropriate
      handling was one of the primary motivations for the model
      developed here.

      However, at least from the viewpoint of this author, one important
      question remains: assuming that the IDN WG's work is carefully
      confined to characters and identifiers, does the value of local-
      language identifiers justify putting non-ASCII strings into the
      DNS even if end users never see them?  We argue in section 2.1
      that it is not necessary and poses some risks.  However, the
      "variables in programming languages" analogy and the "local
      directory or cache" approach, both outlined above, suggest that
      such names would be extremely useful and fairly safe if the limits
      of code-point-level matching and identifier-only use are taken
      narrowly and observed conservatively [ICANN-Permitted].  And, if
      one believes the model outlined here, or any competing "keyword"
      model (see next section), will achieve wide deployment and use,
      the needs and perspectives of such systems should condition the
      evaluation of IDN WG-produced alternatives.  So there is a serious
      and complex set of engineering (and, realistically, political)
      tradeoffs to be evaluated in making the decision as to whether
      wide deployment of some version of the IDN work is appropriate.

5.2 "Keyword" systems

      In the Internet object-referencing context, the term "keyword
      system" has been used to refer to many different things.  Many
      would fit nicely into the localized search environment, but most
      of the existing proposals put them directly on top of the DNS, or
      skip the DNS entirely and go directly to IP addresses.  The
      difficulty with these systems is that they either must be
      localized (e.g., a different system or database for each language,
      country, or smaller locality) or they don't scale well.  Arguably,
      some don't scale well even if localized.  In particular, they
      eventually suffer from either the "all the good names are taken"
      problem (of which the DNS is frequently accused) or they are very
      vulnerable to poor retrieval precision properties as the number of
      names (or keyword combinations) in the name space grows large.
      I.e., like so many other ideas for the global Internet, they work
      in constrained environments, but cannot adjust well to large

      Adapting bibliographic styles of keyword systems to operate
      locally as part the models proposed here would appear to be the
      best way forward for such systems.  It has been observed that what
      most users really want most of the time is localization, and
      locally-oriented keyword systems could satisfy much of that
      requirement.  Keyword systems would also be strengthened by being
      placed on a base of use and language-sensitive naming and
      searching, and a very strong local cache, rather than on the low-
      context, monohierarchical, DNS.

      Other types of keyword systems, including the one described by
      Arrouye and Popp [Arrouye], are really special cases of the global
      faceted search service.  They rely on careful selection of names
      (and, consequently, resolution of "best fit" and "rights") to
      achieve uniqueness and, hence what they describe as "direct
      navigation" (see elsewhere in this document).  Similar systems
      might utilize a set of keywords combined into a phrase that can be
      interpreted, possibly with permutation rules, in a search service.
      In the interest of simplification and presenting simple names to
      users, these systems are likely to omit most or all of the non-
      name string facets from user-visible search interfaces.  Some
      further analysis, as to whether what is optimally desirable is a
      set of unordered keywords, or an ordered phrase that might contain
      such keywords, seems called for.  Different answers could, of
      course, be implemented in different components of this model.

5.3 Client-side and server-side solutions

      IDNA, and other key approaches considered during the IDN WG's
      deliberations, are essentially client implementations, applied to
      names before they are placed in the DNS and to queries before they
      are passed to the DNS.  This contrasts with the existing use and
      protocols of DNS in which, e.g., string matching is done on the
      server.  Ignoring speed of deployment (which can be argued either
      way), the advantage of client-side implementations is that they
      don't require changes to the DNS fabric itself (and therefore
      minimize the risk of damaging existing applications that rely on
      that fabric).  Because the mechanisms discussed here do not rely
      on the DNS for any searching or matching activities, and are
      completely new, server-side implementations are again feasible:

      applications will require modification to access these services
      (just as they would to support a client-side implementation), but
      older, unmodified, applications will not touch them at all.

      Server-side implementations have several advantages over client-
      side ones.  If something complicated is being done, it is often
      possible to apply more computer resources, or larger tables, on a
      server, and to update those resources and tables more easily if
      needed.  And server-side implementations tend to yield more
      uniformity of behavior relative to having a potentially wide mix
      of client implementations.

      However, integrity protection procedures that depend on similar
      computations on client and server, such as those that rely on
      digital signatures computed over the data, may not eliminate the
      requirement for client-side computations.  See section 10.

6  Comments on business models

   Historically, the IETF has had even less desire to involve itself
   with business models than it has with user interfaces (see section
   3.5).  But the approach outlined here, and the protocol and
   operational proposals that will derive from it, face a particular
   challenge: the DNS works well for its intended purpose (something we
   don't intend to change) and arguably works at least tolerably for
   some purposes, including as a search engine, for which it was not
   intended.  Many of us see its quality and capabilities, when used as
   a search (or, more accurately, "guessing") engine deteriorating.
   Collapse, if it occurs, is still in the future if it occurs at all,
   although recent trends seem to point to less dependence on the DNS
   before that system passes its critical point (see [DNSROLE] for more
   discussion on this topic).   There are also considerable vested
   interests -- both economic and policy control-- associated with the
   current DNS structure and arrangements.

   The ability to produce and deploy a different model, especially one
   that requires new work in several areas, against that backdrop will
   be challenging at best.  Unless there are clear business models for
   doing so, the odds of success are quite low.  So this section
   outlines some of the business issues and models not covered elsewhere
   in this document.  As with the user interface discussion, it is not
   intended to be definitive: some of these models may fail and others
   may be more attractive.  But it is intended to provide a sufficient
   demonstration of concept to perhaps permit the technical ideas to be
   taken seriously.

   We observe that a telephone system analogy may be helpful.  With the
   telephone system, there are registries, described as national
   numbering databases, that record which numbers are in use and by
   whom.  There are white pages services which, given locale and some
   other information (e.g., whether business or residential in some
   areas) and a near or exact match to a name, provide name to number
   lookup.  And there are yellow pages services, with precise categories
   and organization differing somewhat from one location to another.
   Organizations make money at all three levels, but the greatest
   aggregate income occurs with the yellow pages services.

   At each of sublayers two and three, there are multiple services.
   Some of these would probably need to be operated as public goods,
   spreading costs over the producers of other services.  Others would
   presumably be directly profitable.

6.1 Faceted global searching

6.1.1 Facet listings and identification

   For the attribute facets that rely on controlled vocabularies, some
   organizational structure would be required to oversee those
   vocabularies.  As suggested elsewhere, the ideal would be to use pre-
   existing organizations and pre-existing lists (the WIPO
   classification of goods and services [NICE] is an example of such a
   list, as would be the IS 3166-1 list traditionally used for country
   code domain names.  Where such lists did not exist, it would be
   necessary to build arrangements for them.  The maintenance of such
   vocabularies would, from a global Internet standpoint, be a public

6.1.2 Registration and searching

   Actual registrations would be required for names and their attributes
   with, as mentioned above, multiple registrations when an individual,
   organization, or business wished to be registered with more than one
   attribute set.  The economic model would presumably parallel the
   current registrar and registry business, with a charge for
   registration (since there is no intrinsic requirement for a single
   registry, registry services might well be competitive, eliminating
   the need for models that separate registries and registrars.
   However, lookup and search activities would be more flexible than the
   DNS, with extended services, including character set transposition,
   language translation, and potentially more extensive search
   variations being potential areas on which providers could compete,
   using fee for service or subscription models to support costs.

6.2 Localized and topical databases and searching

   As mentioned above, yellow pages and publication of directories and
   guidebooks are traditionally where the money has been made.  The
   analogies apply: one could imagine charging for entering information
   into the databases, or for searching, or for information delivered,
   or all three of these.  And all have been used for papers and related

7  Glossary

   <<See Placeholder>>


   Encoding form


   Keyword (see section <<4.2>>)

   Multilingual name (see section <<4.1>>)

8  Summary

   The solution to the "multilingual DNS" problem, and to a series of
   other limitations of the DNS relative to today's expectations for
   naming and searching, lies in solutions targeted to those problems,
   rather than superimposing additional mechanisms on the DNS in ways
   that, those who advocate them hope, will not cause problems with
   older programs and unconverted infrastructure.  Inserting new search
   layers avoids those risks and permits a clean solution that is
   adapted to the problems, rather than the limitations imposed by
   existing properties of the DNS.

9  IANA Considerations and related topics

   At search layer two, it is difficult to think about how the system
   might function successfully without controlled vocabularies for each
   of the non-name facets.  As discussed in section 2.2, we have already
   established one such registry (bound to an ISO standard), and
   mechanisms for utilizing it, with RFC 3066.  The Madrid agreement and
   its predecessors [NICE] provide classifications for types of
   businesses, but we would need to extend the registry for names that
   are not business-related.  The two locational attributes are somewhat
   vague at this point, but controlled vocabularies would presumably be
   needed, and should, if possible, be drawn from stable, non-IETF, work
   (e.g., IS 3166-1 and 3166-2 might provide a foundation, and possibly
   a complete list, for the location vocabulary).  Curiously, there is
   no technical reason why the name-strings themselves must be unique:
   that is one of the attractions of a model like this over attempting
   to overload the DNS.  If conflicts or confusion occur, those are
   standard civil (marketplace or trademark) issues that can be resolved
   in their own environments, rather than posing special Internet

10 Security Considerations

   Additional layers of naming, searching, and databases imply addition
   of opportunities for compromising those databases and mechanisms.
   Part of the challenge with the model implied here is to determine how
   to secure and authenticate those databases and access (especially
   modify access) to them.  The good news is that, since the functions
   are new, we should be able to design security mechanisms in, rather
   than --as with the DNS-- have to try to graft them on to a structure
   not designed for them.

   A particular issue is integrity protection of responses and possibly
   queries, analogous to the capabilities DNSSec is expected to provide
   for the DNS [DNSSEC].  It would be desirable to avoid having to make
   potentially-complex signature computation on both clients and servers
   (as in DNS).  One approach would be to authenticate the source and
   verify transmission integrity, but that may or may not be sufficient.

11 References

   Most of the references in this document are to examples of approaches
   to the systems outlined here, or provide additional information about
   the context of some of the suggestions, or are included to give
   credit for particular ideas or to better identify earlier and
   approaches.  None of those references are normative in the protocol
   sense typically used in the IETF.

   11.1. Normative References

   [ISO639] ISO 639:1988 (E/F) - Code for the representation of names of
   languages - The International Organization for Standardization, 1st
   edition, 1988-04-01

   [ISO3166-2] International Organization for Standardization. "Codes
   the representation of names of countries and their subdivisions --
   Part 2: Country subdivision code".  1998.
        The values provide by this standard, and its use with the
       UN/LOCODE list, are discussed at

   [LangTag] Alvestrand, H. "Tags for the Identification of Languages",
   RFC 3066, January 2001.

   [RFC882] Mockapetris, P.V., "Domain names: Concepts and facilities".
   RFC 882.  Nov-01-1983.

   [RFC883] Mockapetris, P.V. "Domain names: Implementation
   specification", RFC 883. Nov-01-1983.

   [RFC1035] Mockapetris, P.V. "Domain names - implementation and
   specification", RFC 1035. Nov-01-1987.

   [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
   3", BCP 9, RFC 2026, October 1996

   [RFC2826] IAB. "IAB Technical Comment on the Unique DNS Root", RFC
   2826.  May 2000.

   11.2. Explanatory and informative references

   [Arrouye] Arrouye, Yves, et al. "Keyword Lookup Systems As a Class
   of Naming Systems".  Work in progress, draft-arrouye-kls-00.txt, and
   unpublished BOF proposal.

   [Austein] Austein, Rob.  Private communication, 2001.

   [CAS-string] Lee, XD., "Chinese name string in search-based access
   model for the DNS", work in prgress, draft-xdlee-cnnamestr-00.txt.

   [CNRP] Popp, N., M.  Mealling, L. Masinter, K. Sollins. "Context and
   Goals for Common Name Resolution", RFC 2972, October 2000.

   [DNSROLE] Klensin, J., "Role of the Domain Name System", work in
   progress, draft-klensin-dns-role-03.txt (June 2002)

   [IS10646] ISO/IEC 10646-1:2000 Information technology -- Universal
   Multiple-Octet Coded Character Set (UCS) -- Part 1: Architecture and
   Basic Multilingual Plane and ISO/IEC 10646-2:2001 Information
   technology -- Universal Multiple-Octet Coded Character Set (UCS) --
   Part 2: Supplementary Planes.   Often referred to in IETF circles as
   "Unicode", citing the code-point-equivalent Unicode Consortium

   [HOSTNAME] Harrenstien, K., M.K. Stahl, E.J. Feinler.  "Hostname
   Server", RFC 0953, Oct-01-1985.  Also Braden, R., ed. "Requirements
   for Internet Hosts - Application and Support", RFC 1123, October

   [ICANN-Permitted] ICANN IDN Committee, "Briefing Paper on IDN
   Permissible Code Point Problems".  Posted as
   http://www.icann.org/committees/idn/idn-codepoint-paper.htm, February
   2002.  Also see "Internationalized Domain Names (IDN) Committee:
   Final Report to the ICANN Board",
   http://www.icann.org/committees/idn/final-report-27jun02.htm, 27 June

   [IDNA] Faltstorm, P.A., P. Hoffman, A. M. Costello,
   "Internationalizing Domain Names in Applications (IDNA)", work in
   progress (draft-ietf-idn-idna-14.txt, October 2002). Approved by IESG
   for publication as a Proposed Standard, October 2002.

   [LDAP] Wahl, M., T. Howes, S.  Kille. "Lightweight Directory Access
   Protocol (v3)", RFC 2251, December 1997.

   [Mealling-SLS] Mealling, M and L Daigle, "Service Lookup System
   (SLS)", work in progress (draft-mealling-sls-01.txt, June 2002).

   [NAMEPREP] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
   Profile for Internationalized Domain Names", work in progress
   (draft-ietf-idn-nameprep-11.txt, June 2002).  Approved by IESG for
   publication as a Proposed Standard, October 2002.

   [SHI] Shi X., K. Liu, "Caching Mechanisms in Layered DNS Search
   Services", draft in progress (draft-xhshi-dns-search-caching-00.txt,
   October 2002).

   [STRINGPREP] Hoffman, P. and M. Blanchet, "Preparation of
   Internationalized Host Names", work in progress
   (draft-hoffman-stringprep-07.txt, October 2002).  Approved by IESG
   for publication as a Proposed Standard, October 2002.

   [WIPO-NICE] World Intellectual Property Organization, "Nice Agreement
   concerning the International Classification of Goods and Services for
   the Purposes of the Registration of Marks", June 1957.

   [NEWCLASS] Klensin, John, "Internationalizing the DNS -- A New
   Class", work in progress, draft-klensin-i18n-newclass-02.txt (June

   [RealNames] http://www.realnames.com/ -- real reference needed.

   [RFC1591] Postel, J. "Domain Name System Structure and Delegation",
   RFC 1591, March 1994.

   [RFC2345] Klensin, J, T. Wolf, G.  Oglesby. "Domain Names and Company
   Name Retrieval", RFC 2345. May 1998.
       It is perhaps worth noting that, as in the case of many RFCs,
      descriptions of this work were widely circulated in draft form
      and discussed for a year or two before being published as an RFC.

   [RFC2822] Resnick, P., Editor. "Internet Message Format", RFC 2822.
   April 2001.

   [RFC2825] IAB, L. Daigle, ed. "A Tangled Web: Issues of I18N, Domain
   Names, and the Other Internet protocols", RFC 2825.  May 2000.

   [THES] International Organization for Standardization. "Information
   and documentation -- Vocabulary" ISO 5127:2001.

   [RFC-URI] Berners-Lee, T., R. Fielding, L. Masinter. "Uniform
   Resource Identifiers (URI): Generic Syntax", RFC 2396.  August 1998.

   [WAIS] M. St. Pierre, J. Fullton, K. Gamiel, J.  Goldman, B.
   Kahle, J. Kunze, H. Morris, F. Schiettecatte.  "WAIS over
   Z39.50-1988", RFC 1625.  June 1994.

   [Z39] International Organization for Standardization. "Information
   and documentation -- Information retrieval (Z39.50) -- Application
   service definition and protocol specification", ISO 23950:1998.

12 Acknowledgments

   This document, and some related notes, are the result of thinking
   that has come together and evolved since before the issue of
   internationalized access to domain names came onto the IETF's radar.
   Discussions with a number of people have led to refinements in the
   approach or the text, even though some of them might not recognize
   their contributions or agree with the conclusions I have drawn from
   them (indeed, some of those discussions were rooted in challenges to
   the general ideas expressed here).  Particularly important
   suggestions have come from, or arisen out of conversations with, Ran
   Atkinson, Harald Alvestrand, Rob Austein, Fred Baker, Christine
   Borgman, Eric Brunner-Williams, Randy Bush, Tim Casey, Vint Cerf,
   Kilnam Chon, Dave Crocker, Leslie Daigle, Patrik Faltstrom, Michael
   Froomkin, Francis Gurry, Marti Hearst, Paul Hoffman, Kenny Huang,
   Marylee Jenkins, Dongman Lee, Xiaodong Lee, Karen Liu, Mao Wei,
   Michael Mealling, Erik Nordmark, Gary Oglesby, Mike Padlipsky, Qian
   Huilin, James Seng, Theresa Swinehart, Tan Tin Wee, Len Tower, and
   Zita Wenzel, as well as some memorable long-ago conversations with
   Jon Postel and J.C.R. Licklider.

   The first version of this Internet Draft was posted in May 2001,
   after fairly extensive public discussion of the underlying issues and
   required technology during the preceeding nine months.

13 Author's Address

   John C Klensin
   1770 Massachusetts Ave, #322
   Cambridge, MA 02140

14 Major changes between version 04 and 05

   After considerable discussion (little of it, unfortunately, involving
   the IRNSS list) about return values and "layering", this version
   considerably restructures the model of both.   In the return value
   case, the output of faceted search is now specified as containing one
   or more URIs, not just DNS name(s).  There is some discussion of the
   motivation for this in the text, but the key issue is that users are
   almost certain to search for resources that make sense to them: the
   distinction between a DNS name and a URI is too subtle and the latter
   does not adequately locate user-visible resources.

   The layering issue is more significant, at least in terms of this
   work and how it has been presented.  Our original assumption was that
   the localized and topical searches would rest on top of the faceted
   ones, producing faceted values as outputs.  After more discussion and
   examination of likely cases, it has become clear that the two are
   better thought of as independent and complementary models, with each
   other and with web searches -- all still layered on top of the DNS.
   The text has been changed to reflect this, but might not yet be
   completely consistent with it.  Pointers to omissions would be

15 Placeholders

   For some reason, new ideas or approaches, or ways of presenting or
   clarifying existing ones, seem to arise immediately before a version
   of this document is submitted for posting.  It has often been
   impossible to properly incorporate these.  The following are pending,
   and will be picked up in the next revision:

   (i) A new section (3.3.3) on "Discussion of Industry Types" that will
   introduce a better model (and less handwaving) for handing industry
   type codes where they are appropriate and structuring data for that
   facet for other types of names.  Version 05 contains the beginnings
   of that discussion.

   (ii) Section 3.6.3 should be reviewed with people who actually
   understand the language and issues and then rewritten (this task may
   have been superceded by the ongoing work with [JET-Guideline]).

   (iii) Section 3.6.4, which is now just an outline, needs to be filled

   (iv) Completion of the glossary, which seems to be necessary for
   readers who have not been immersed in, e.g., the discussions of the
   IDN WG.  This work is being held pending the outcome of discussions
   about draft-hoffman-i18n-terminology.

   (v) Section 3.6.1, as originally prepared for draft version 02, was
   not coherent and has been replaced.  The material there on the
   textual ("comment") field should be carefully reviewed -- it may not
   be right.    (From 04 -- no comments yet received.)

   (vi) The new section 2.2.6 still needs to be written and inserted.

   (vii) In versions prior to -04, section 3 was largely a discussion of
   search layer two (i.e., global faceted search) issues, with a few
   asides about search layer three (i.e., localized search).  With
   version 04, that distinction has been made explicit and a new section
   four inserted as a placeholder for a similar discussion about search
   layer three.  That section should be supplied for version 05.

   Expires May 2003