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RFC 2655 - CIP Index Object Format for SOIF Objects


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Network Working Group                                           T. Hardie
Request for Comments: 2655                                        Equinix
Category: Experimental                                          M. Bowman
                                                                 Transarc
                                                                 D. Hardy
                                                                 Netscape
                                                              M. Schwartz
                                                            Affinia, Inc.
                                                               D. Wessels
                                                                    NLANR
                                                              August 1999

                CIP Index Object Format for SOIF Objects

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

1.  Abstract

   The Common Indexing Protocol (CIP) allows servers to form a referral
   mesh for query handling by defining a mechanism by which cooperating
   servers exchange hints about the searchable indices they maintain.
   The structure and transport of CIP are described in (Ref. 1), as are
   general rules for the definition of index object types.  This
   document describes SOIF, the Summary Object Interchange Format, as an
   index object type in the context of the CIP framework.  SOIF is a
   machine-readable syntax for transmitting structured summary objects,
   currently used primarily in the context of the World Wide Web.

   Query referral has often been dismissed as an ineffective strategy
   for handling searches of Web resources, and Web resources certainly
   present challenges not present in structured directory services like
   Rwhois.  In situations where a keyword-based free text search is
   desired, query referral is not likely to be effective because the
   query will probably be routed to every server participating in the
   referral mesh.  Where a search can be limited by reference to a
   specific resource attribute, however, query referral is an effective
   tool.  SOIF can be used to create such a known-attribute query mesh
   because it provides a method for associating attributes with net-
   addressable resources.

1.1 History

   SOIF was first defined by the Harvest project [Ref 2.] in January
   1994.  SOIF was derived from a combination of the Internet Anonymous
   FTP Archives IETF Working Group (IAFA) templates [Ref 3.] and the
   BibTeX bibliography format [Ref 4.].  The combination was originally
   noted for its advantages of providing a convenient and intuitive way
   for delimiting objects within a stream, and setting apart the URL for
   easy object access or invocation, while still preserving
   compatibility with IAFA templates.

   Mic Bowman, Darren Hardy, Mike Schwartz, and Duane Wessels each
   contributed to the creation of the SOIF format as part of the Harvest
   Project; later work took place as part of the FIND working group.

2.  Name

   The index object described below will have the MIME type of
   application/index.obj.HARVEST-SOIF-1.

3.  Payload Format

   Each summary object has 3 fundamental components: a template type, a
   URL, and zero or more ATTRIBUTE-VALUE pairs.  Because the VALUEs in
   the ATTRIBUTE-VALUE pairs may contain arbitrary data (cf. Section
   3.5), SOIF objects should be encoded in Base64 unless the template
   type unambiguously establishes that the VALUEs do not contain binary
   data.

3.1  Template Type

   The Template type is used to identify the set of ATTRIBUTEs contained
   within a particular SOIF object.  SOIF does not define the template
   types themselves; it only provides a way to associate the summary
   object with a predefined template type name.  Template types may be
   registered or unregistered.  Unregistered template types provide an
   indication of available ATTRIBUTE-VALUE pairs, but these may vary
   both according to the original resource and the method by which the
   summary object was generated.  Registered template types must refer
   to a formally specified description of all mandatory and optional
   ATTRIBUTE-VALUE pairs available for that type.  See [10] for a
   description of the process of registering template types with the
   IANA.

   Historically, the template types used by SOIF were derived from IAFA
   template types (Ref. 3). SOIF objects generated by the Harvest system
   have a "FILE" template type; in current practice this is the most
   common template type.  The "FILE" template type is a generic template

   type meant to handle a large variety of web-based resources.  No
   formal specification of it is available, though a list of ATTRIBUTE-
   VALUE pairs common to the "FILE" template type is found in Appendix
   A.  "DOCUMENT" and "OBJECT" are other generic template-types.

   The use of unregistered template types obviously presents some
   problems to the correct operation of query referral.  Two efforts
   have been mounted to allow peer-to-peer agreement on the association
   of template types with specific attribute sets: Netscape's RDM (Ref.
   6) and the STARTS project (Ref. 7).  Initially, CIP meshes based on
   systems which use unregisterested template types may need to use
   these or similar methods to associate template types with specific
   attribute sets.

   Mesh operators are strongly encouraged, however, to migrate to
   registered template types as soon as is practical.  Registered
   template types allow CIP meshes to derive the definitions of
   attributes, which enables multiple-language interfaces to the base
   attributes.  In addition, registered template types allow CIP meshes
   and other users of SOIF to establish the permitted data types and
   encodings of the VALUEs associated with each ATTRIBUTE.  This makes
   deriving the appropriate matching semantics for a particular VALUE
   much more straightforward and eliminates the limitations of the
   default octet-by-octet matching (cf. Section 4.).

3.2  URL

   Uniform Resource Locators (URLs) (Ref 5.) are used by SOIF as object
   IDENTIFIERs.  SOIF associates its summary objects with net-
   addressable resources by using the URL by which the resource was
   addressed as the initial field of the object body.  See section 3.4
   for the formal grammar associated with SOIF objects.

   This association allows the same resource to have multiple summary
   objects, differentiated only by the URL by which the resource was
   accessed.  This possibility does not, however, impact the usability
   of the URL as an object IDENTIFIER. Furthermore, since it can be
   argued that the net address is a salient part of the metadata, there
   may be compensating benefits to using the URL as an object
   IDENTIFIER.

   As noted in Appendix A, the Harvest project used several additional
   identity attributes ("Gatherer-Name", "Gatherer-Host", "Gatherer-
   Port" and "Gatherer-Version") to further identify the provenance of a
   particular object.  Within the context of CIP, it may be useful to
   identify the base sources of particular index objects; see Appendix B
   for one example of how a SOIF-based CIP hint could use the base
   source URL.

3.3  ATTRIBUTE-VALUE pairs.

   Each summary object has zero or more ATTRIBUTE-VALUE pairs, which
   contain metadata about the net-addressable resource referenced by the
   URL.  Pairs are composed of an ATTRIBUTE IDENTIFIER, the length of
   the VALUE, a delimeter, and the VALUE.  It should be stressed that
   ATTRIBUTE VALUE pairs are not CR/LF terminated, but parsed according
   to grammar set out in section 3.4.  In the examples in Section 3.6
   and in many other representations of SOIF objects, ATTRIBUTE-VALUE
   pairs are represented on individual lines to enhance readability.
   VALUEs may contain CR/LF, however, and implementors must be careful
   to parse the full VALUE.  Implementors of SOIF parsers MUST ignore
   <CR>,<LF>,<TAB>,<SPACE>, or other whitespace found between the VALUE
   of an ATTRIBUTE-VALUE pair and the ATTRIBUTE-IDENTIFIER of the
   subsequent pair.

   The SOIF syntax does not explicitly allow for a single ATTRIBUTE to
   have multiple VALUEs.  To handle multiple VALUEs for the same
   ATTRIBUTE, SOIF uses an ATTRIBUTE naming convention; a hyphen and
   positive integer are appended to the ATTRIBUTE name to create an
   ATTRIBUTE IDENTIFIER VALUE associated with a specific ATTRIBUTE.  For
   example, the ATTRIBUTE IDENTIFIERs "Author-1", "Author-2", and
   "Author-3" can be used to represent three VALUEs associated with the
   ATTRIBUTE "Author" where a specific resource has three authors.  See
   section 4 for the implications of this strategy on matching
   semantics.

3.4  SOIF Grammar

   The SOIF syntax is defined by the following grammar:

      SOIF            ::=  OBJECT SOIF |
                           OBJECT
      OBJECT          ::=  @ TEMPLATE-TYPE { URL ATTRIBUTE-LIST }
      TEMPLATE-TYPE   ::=  IDENTIFIER
      ATTRIBUTE-LIST  ::=  ATTRIBUTE ATTRIBUTE-LIST |
                           ATTRIBUTE |
                           NULL
      ATTRIBUTE       ::=  IDENTIFIER {VALUE-SIZE} DELIMITER VALUE
      URL             ::=  RFC1738-URL-Syntax | "-"
      IDENTIFIER      ::=  ALPHA-NUMERIC-STRING
      VALUE           ::=  ARBITRARY-DATA
      VALUE-SIZE      ::=  NUMERIC-STRING
      DELIMITER       ::=  ":<TAB>"

3.5   Grammar Description

   URL
      a Uniform Resource Locator encoded in the syntax defined by RFC
      1738 [3].  If the summary object has no URL associated with it,
      then a Latin-1 hyphen (octal \055) is used instead.

   IDENTIFIER
      an ASCII character string that only contains alphanumeric
      characters and hyphens or underscores.  IDENTIFIERs should avoid
      including hyphens followed by positive integers except when
      constructing multiple-VALUE ATTRIBUTE IDENTIFIERs.

   VALUE
      a buffer of VALUE-SIZE octets containing the VALUE.  The VALUE may
      contain data in arbitrary formats or encodings, which recipients
      recognize based on Template-Type.

   VALUE-SIZE
      a non-negative integer encoded as an ASCII character string.  The
      integer indicates how many octets the VALUE occupies after the
      DELIMITER.

   DELIMITER
      a two octet delimiter which is a Latin-1 colon (:) and a tab (\t),
      (octal \072\011).

   { }  the Latin-1 curly braces (octal \173 and \175) are used to wrap
      the VALUE-SIZE (no spaces) as well as the URL and ATTRIBUTE-LIST
      combination.

   @TEMPLATE-TYPE
      the Latin-1 @ (octal \100) and TEMPLATE-TYPE (no space between
      them) is used to mark the beginning of the SOIF object.

   NUMERIC-STRING
      Zero or more ASCII numerals.

   ALPHA-NUMERIC-STRING
      Zero or more ASCII letters or numerals, plus hyphens or
      underscore.  [a-z,A-Z,0-9,- and _].

   ARBITRARY-DATA
      Octets of data in arbitrary formats or encodings.

4.  Matching Semantics

   As was discussed in Section 1, query referral of SOIF objects will be
   most effective when a query identifies a particular ATTRIBUTE or set
   of ATTRIBUTEs as the target of the query match.  A query-identified
   ATTRIBUTE should be considered to match a SOIF ATTRIBUTE when a
   case-insentive character-by-character comparison matches that portion
   of the ATTRIBUTE IDENTIFIER prior to any hyphen-integer suffix.  For
   example, a query which asks for a match on the ATTRIBUTE "author"
   should match the IDENTIFIERs "author", "Author", "AUTHOR", and
   "Author-1".  [10] discourages the registration of template types
   containing ATTRIBUTEs which have previously been registered with
   substantially different definitions.  This will help eliminate mis-
   referral, but a CIP mesh may nonetheless need to maintain a thesaurus
   matching ATTRIBUTEs from particular template-types to those of other,
   especially unregistered, template-types.

   The matching semantics appropriate for a particular VALUE are derived
   from its data type and encoding.  For VALUEs associated with
   ATTRIBUTEs which are part of a registered template type, the data
   type and encoding are readily available.  For VALUEs associated with
   ATTRIBUTES associated with unregistered template-types, an octet-by-
   octet comparison is the default.  In cases where previous experience
   has demonstrated that a particular ATTRIBUTE contains string data, a
   case-insensitive substring match may be used.  For example, in a
   query against the "AUTHOR" ATTRIBUTE of the generic "DOCUMENT"
   template type, the query VALUE "Garcia" should match the SOIF VALUEs
   "Garcia", "GARCIA", and "Jose Garcia y Montes".

   Over time, there may well emerge an understanding of which attributes
   tend to produce correct query referrals within a mesh.  As such
   understandings emerge, mesh maintainers may wish to define a
   particular SOIF TEMPLATE-TYPE which restricts included ATTRIBUTES to
   those likely to foster correct referrals.

5.  Internationalization

   The internationalization of SOIF depends on the registration of
   template-types.  Since TEMPLATE-TYPEs and ATTRIBUTE IDENTIFIERs must
   be in ASCII characters, only languages which use the ASCII character
   set are fully supported for unregistered TEMPLATE-TYPEs.  For
   registered template types, in contrast, the specification of an
   ATTRIBUTE's definition will allow UI designers to present a native-
   language mapping of the ATTRIBUTE to the end user.  Further, the
   inclusion of data type and encoding information in the description of
   VALUEs means that any language encoding or character set required by
   a particular application may be supported.  For unregistered template
   types, the ability of peer servers to pass schema definitions may

   provide a form of "private registration" which could provide some of
   the facilities for internationalization available to registered
   template types.  (See above, section 3.1 and Refs. 6 and 7.)

6.  Example Summary Objects

   The appendices contain example summary objects encoded using specific
   template types.  The following are some example summary objects using
   the generic "DOCUMENT" SOIF template-type:

   @DOCUMENT { http://home.netscape.com:80/
   Title{19}:  Welcome to Netscape
   Content-Type{9}:    text/html
   Content-Length{5}:  33262
   }

   @DOCUMENT { http://home.netscape.com/eng/ssl3/ssl-toc.html
   Title{19}:  SSL Protocol V. 3.0
   Content-Type{9}:    text/html
   Content-Length{5}:  5870
   Author-1{14}:   Alan O. Freier
   Author-2{14}:   Philip Karlton
   Author-3{14}:   Paul C. Kocher
   Abstract{318}:  This document specifies Version 3.0 of the
   <B>Secure Sockets Layer (SSL V3.0)</B> protocol, a security
   protocol that provides communications privacy over the Internet.
   The protocol allows client/server applications to communicate in
   a way that is designed to prevent eavesdropping, tampering, or
   message forgery.
   }

   @DOCUMENT { http://www.nissanmotors.com/1996/300ZX/pictures/300zx.jpg
   Content-Type{10}:    image/jpeg
   Content-Length{5}:  25940
   Last-Modified{31}:  Tuesday, 11-Jun-96 19:18:44 GMT
   Thumbnail{259}:     ..................
   }

7.  Security

   Please see (Ref. 1) for a general discussion of Security concerns for
   the CIP framework.

   SOIF currently contains no requirement that any template type contain
   an authentication ATTRIBUTE.  SOIF summary objects lacking
   authentication ATTRIBUTEs must, therefore, be treated as unreliable
   indicators of the referenced resource's content.  A hostile party
   could create a summary object which significantly misrepresented a

   resource's content.  As part of a CIP mesh, this data could either
   channel a large number of requestors to a resource (possibly
   resulting in a denial of service) or away from a resource (possibly
   resulting in a loss of appropriate visibility).

8.  References

   [1]  Allen, J. and M. Mealling, "The Architecture of the Common
        Indexing Protocol (CIP)", RFC 2651, August 1999.

   [2]  The Harvest Information Discovery and Access System:
        <URL:http://harvest.transarc.com/>.

   [3]  D. Beckett, IAFA Templates in Use as Internet Metadata, 4th
        Int'l WWW Conference, December 1995,
        <URL:http://www.hensa.ac.uk/tools/www/iafatools/>

   [4]  L. Lamport, LaTeX: A Document Preparation System, Addison-
        Wesley, Reading, Mass., 1986.

   [5]  Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform Resource
        Locators (URL)", RFC 1738, December 1994.

   [6]  D. Hardey, Resource Description Messages (RDM), W3C Note-rdm-
        960724, July 24, 1996, <URL:http://www.w3.org/pub/WWW/TR/NOTE-
        rdm.html>

   [7]  L. Gravano, K. Chang, H. Garcia-Molina, C. Lagoze, A. Paepcke,
        STARTS: Stanford Protocol Proposal for Internet Retrieval and
        Search, January 1997, <URL:http://www-
        db.stanford.edu/~gravano/starts.html>

   [8]  S. Weibel, J. Kunze, C. Lagoze, Dublin Core Metadata for Simple
        Resource Description, Work in Progress.

   [9]  E. Miller, Dublin Core Element Set Crosswalk, January 1997,
        <URL:http://www.oclc.org:5046/~emiller/DC/crosswalk.html>

   [10] Hardie, T., "Registration Procedures for SOIF Template Types",
        RFC 2656, August 1999.

9.  Authors' Addresses

   Ted Hardie
   Equinix
   901 Marshall Street
   Redwood City, CA 94063 USA

   EMail: hardie@equinix.com

   Mic Bowman
   Transarc Corporation
   The Gulf Tower
   707 Grant Street
   Pittsburgh, PA 15219 USA

   Phone: +1 412 338 4400
   EMail: mic@transarc.com

   Darren Hardy
   Netscape Communications Corp.
   685 E. Middlefield Road
   Mountain View, CA 94043 USA

   Phone: +1 415 937 2555
   EMail: dhardy@netscape.com

   Mike Schwartz
   Affinia, Inc.
   621 17th Street, Suite 1700
   Denver, CO 80293

   Phone: +1 (303) 292-4818
   E-mail: mfs@affinia.net

   Duane Wessels
   National Laboratory for Applied Network Research

   Phone: +1 303 497 1822
   EMail: wessels@nlanr.net

Appendix A.

   Common Attributes for "FILE" Template-type Summary Objects created by
   Harvest:

   Abstract
      Brief abstract about the object.

   Author
      Author(s) of the object.

   Description
      Brief description about the object.

   File-Size
      Number of bytes in the object.

   Full-Text
      Entire contents of the object.

   Gatherer-Host
      Host on which the Gatherer ran to extract information from the
      object.

   Gatherer-Name
      Name of the Gatherer that extracted information from the object.
      (eg. Full-Text, Selected-Text, or Terse).

   Gatherer-Port
      Port number on the Gatherer-Host that serves the Gatherer's
      information.

   Gatherer-Version
      Version number of the Gatherer.

   Update-Time
      The time that Gatherer updated the content summary for the object.

   Keywords
      Searchable keywords extracted from the object.

   Last-Modification-Time
      The time that the object was last modified.

   MD5
      MD5 16-byte checksum of the object.

   Refresh-Rate
      The number of seconds after Update-Time when the summary object is
      to be re-generated.  Defaults to 1 month.

   Time-to-Live
      The number of seconds after Update-Time when the summary object is
      no longer valid.  Defaults to 6 months.

   Title
      Title of the object.

   Type The object's type. Some example types are:

         Archive
         Audio
         Awk
         Backup
         Binary
         C
         CHeader
         Command
         Compressed
         CompressedTar
         Configuration
         Data
         Directory
         DotFile
         Dvi
         FAQ
         FYI
         Font
         FormattedText
         GDBM
         GNUCompressed
         GNUCompressedTar
         HTML
         Image
         Internet-Draft
         MacCompressed
         Mail
         Makefile
         ManPage
         Object
         OtherCode
         PCCompressed
         Patch
         Perl
         PostScript

         RCS
         README
         RFC
         SCCS
         ShellArchive
         Tar
         Tcl
         Tex
         Text
         Troff
         Uuencoded
         WaisSource

   Update-Time
      The time that the summary object was last updated.  REQUIRED
      field, no default.

   URL-References
      Any URL references present within HTML objects.

Appendix B.

   Proposed Attributes for a "CIP-HINT" Template Type

   Attribute-Identifier-List
      A comma-delimited list whose entries take the form Template-
      Type:Attribute .  This list identifies the attributes against
      which queries are supported.  Because of the current limitation on
      Identifiers, this list must be in ASCII.

   Source
      The URI of the service which created some or all of the index
      objects to which this hint applies.  Note that this service may be
      and often is distinct from the server which provides query access
      to those objects.

   Total-Object-Count
      The total number of index objects in the collection for which the
      Hint applies.  This should be a positive integer.

   Weightlist-[Attribute-Identifier]
      This construction allows the HINT to contain a weighted list of
      values for a specific Attribute-Identifier.  There may be as many
      Weightlist entries as there Attribute-Identifiers in the
      Attribute-Identifier-List.  Each Weightlist entry takes the form
      of Value;Object-Count, where the object count is a positive
      integer representing the number of objects within the collection
      which contain that value. Weightlists are comma- delimited.

      Should a Value contain a comma, it should be escaped when
      incorporated into the weightlist.

   Threshold-[Attribute-Identifier]
      If a server wishes not to report infrequently occurring Values in
      a specific Weightlist, it may declare a threshold under which it
      will not report Values.

   Certification-Type
      The type of Certification used for this object

   Certification
      The Value of the Certification.

   Date
      The Date at which the hint was generated

   Example:

@CIP-HINT{ http://nic.nasa.gov:80/Harvest/brokers/NASA/
Attribute-Identifier-list{49}:
DOCUMENT:Author, DOCUMENT:Keywords, IMAGE:Subject
Source-1{45}: http://nic.nasa.gov/Harvest/gatherers/Eureka/
Source-2{46}: http://techreports.larc.nasa.gov/cgi-bin/NTRS/
Total-Object-Count{5}:    10000
Weightlist-[IMAGE:Subject]{40}:
Shuttle;100, Planet;227, Moon;15, Sun;33
Threshold-[IMAGE:Subject]{2}:     10
Weightlist-[DOCUMENT:Author]{49}:
Grizzard;12, Aldrin\, Buzz;15, Aldrin\, James;45,
Threshold-[DOCMENT:Author]{1}:    5
Certification-Type{13}:   PGP-Signature
Certification{51}: mQCNAzFNm5QAAEEALUBOolOWKpby+=YtmtBxUZWQgSGFyZGllID
Date{29}:  Sun, 05 Jan 1997 08:33:33 GMT
}

Appendix C.

   A "Dublin-Core" Template Type [Ref. 8,9]

   TITLE
      The name given to the resource by the CREATOR or PUBLISHER.

   CREATOR
      The person(s) or organization(s) primarily responsible for the
      intellectual content of the resource.  For example, authors in the
      case of written documents, artists, photographers, or illustrators
      in the case of visual resources.

   SUBJECT
      The topic of the resource, or keywords or phrases that describe
      the subject or content of the resource.  The intent of the
      specification of this element is to promote the use of controlled
      vocabularies and keywords.  This element might well include
      scheme-qualified classification data (for example, Library of
      Congress Classification Numbers or Dewey Decimal numbers) or
      scheme-qualified controlled vocabularies (such as Medical Subject
      Headings or Art and Architecture Thesaurus descriptors) as well.

   DESCRIPTION
      A textual description of the content of the resource, including
      abstracts in the case of document-like objects or content
      descriptions in the case of visual resources.  Future metadata
      collections might well include computational content description
      (spectral analysis of a visual resource, for example) that may not
      be embeddable in current network systems.  In such a case this
      field might contain a link to such a description rather than the
      description itself.

   PUBLISHER
      The entity responsible for making the resource available in its
      present form, such as a publisher, a university department, or a
      corporate entity.   The intent of specifying this field is to
      identify the entity that provides access to the resource.

   CONTRIBUTOR
      Person(s) or organization(s) in addition to those specified in the
      CREATOR element who have made significant intellectual
      contributions to the resource but whose contribution is secondary
      to the individuals or entities specifed in the CREATOR element
      (for example, editors, transcribers, illustrators, and convenors).

   DATE
      The date the resource was made available in its present form.  The
      recommended best practice is an 8 digit number in the form
      YYYYMMDD as defined by ANSI X3.30-1985. In this scheme, the date
      element for the day this is written would be 19961203, or December
      3, 1996.  Many other schema are possible, but if used, they should
      be identified in an unambiguous manner.

   TYPE
      The category of the resource, such as home page, novel, poem,
      working paper, technical report, essay, dictionary.  It is
      expected that RESOURCE TYPE will be chosen from an enumerated list
      of types.

   FORMAT
      The data representation of the resource, such as text/html, ASCII,
      Postscript file,  executable application, or JPEG image.  The
      intent of specifying this element is to provide information
      necessary to allow people or machines to make decisions about the
      usability of the encoded data (what hardware and software might be
      required to display or execute it, for example).  As with RESOURCE
      TYPE, FORMAT will be assigned from enumerated lists such as
      registered Internet Media Types (MIME types).  In principal,
      formats can include physical media such as books, serials, or
      other non-electronic media.

   IDENTIFIER
      String or number used to uniquely identify the resource.  Examples
      for networked resources include URLs and URNs (when implemented).
      Other globally-unique identifiers,such as International Standard
      Book Numbers (ISBN) or other formal names would also be candidates
      for this element.

   SOURCE
      The work, either print or electronic, from which this resource is
      derived, if applicable. For example, an html encoding of a
      Shakespearean sonnet might identify the paper version of the
      sonnet from which the electronic version was transcribed.

   LANGUAGE
      Language(s) of the intellectual content of the resource.  Where
      practical, the content of this field should coincide with the NISO
      Z39.53 three character codes for written languages.

   RELATION
      Relationship to other resources.  The intent of specifying this
      element is to provide a means to express relationships among
      resources that have formal relationships to others, but exist as
      discrete resources themselves.  For example, images in a document,
      chapters in a book, or items in a collection.  A formal
      specification of RELATION is currently under development.  Users
      and developers should understand that use of this element should
      be currently considered experimental.

   COVERAGE
      The spatial locations and temporal durations characteristic of the
      resource.    Formal specification of COVERAGE is currently under
      development. Users and developers should understand that use of
      this element should be currently considered experimental.

   RIGHTS
      The content of this element is intended to be a link (a URL or
      other suitable URI as appropriate) to a copyright notice, a
      rights-management statement, or perhaps a server that would
      provide such information in a dynamic way.  The intent of
      specifying this field is to allow providers a means to associate
      terms and conditions or copyright statements with a resource or
      collection of resources.   No assumptions should be made by users
      if such a field is empty or not present.

   Example:

@Dublin-Core-1 { ftp://ds.internic.net/internet-drafts/
                 draft-kunze-dc-00.txt
TITLE{52}:      Dublin Core Metadata for Simple Resource Description
CREATOR-1{9}:   S. Weibel
CREATOR-2{8}:   J. Kunze
CREATOR-3{9}:   C. Lagoze
SUBJECT{44}:    The Dublin Core Set of Elements for Metadata
DESCRIPTION{46}:        Reference description of Dublin Core elements.
PUBLISHER{31}:  Internet Engineering Task Force
CONTRIBUTOR-1{11}:      Nick Arnett
CONTRIBUTOR-2{15}:      Eliot Christian
CONTRIBUTOR-3{14}:      Martijn Koster
CONTRIBUTOR-4{18}:      Christian Mogensen
CONTRIBUTOR-5{14}:      Timothy Niesen
CONTRIBUTOR-6{11}:      Andrew Wood
CONTRIBUTOR-7{10}:      Mic Bowman
CONTRIBUTOR-8{11}:      Dan Connoly
CONTRIBUTOR-9{15}:      Michael Mauldin
CONTRIBUTOR-10{12}:     Wick Nichols
DATE{16}:       February 9, 1997
TYPE{14}:       Internet draft
FORMAT{4}:      Text
IDENTIFIER:{21} draft-kunze-dc-00.txt
SOURCE{41}:     http://purl.oclc.org/metadata/dublin_core
LANGUAGE{3}:    eng
RELATION{24}:   Draft Reference Standard
COVERAGE{22}:   Expires August 8, 1997
RIGHTS{58}:     Unlimited Distribution;
                readers must not cite as standard.
}

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