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Versions: 00 01 02 rfc2655                                  Experimental
INTERNET-DRAFT                                              Edward Hardie
Expires: April, 1998                                            NASA  NIC
<draft-ietf-find-cip-soif-02.txt>                              Mic Bowman
                                                                 Transarc
                                                             Darren Hardy
                                                                 Netscape
                                                            Mike Schwartz
                                                                    @Home
                                                            Duane Wessels
                                                                    NLANR
                                                            January, 1997




               CIP Index Object Format for SOIF Objects



1.  Status of this Memo

This document is an Internet-Draft.  Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, and
its working groups.  Note that other groups may also distribute working
documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
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.''

To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet- Drafts Shadow
Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe),
ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).

Distribution of this memo is unlimited.  Please send comments to the
authors.

2.  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.

Mic Bowman, Darren Hardy, Mike Schwartz, and Duane Wessels each
contributed to the creation of the SOIF format and to the descriptions
from which this draft is drawn; errors in this description of their work
are the responsibility of Edward Hardie and corrections should be
directed accordingly.

2.1 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.

3.  Name

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

4.  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
4.5), SOIF objects should be encoded in Base64 unless the template
type unambiguously establishes that the VALUEs do not contain binary
data.

4.1  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 [TBD] 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 5.).


4.2  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 4.4 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.


4.3  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 4.4.  In the examples in Section 4.6 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 should 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 5 for the implications
of this strategy on matching semantics.



4.4  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>"



4.5   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 charac-
     ters 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 combi-
     nation.

@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.


5.  Matching Semantics

As was discussed in Section 2, 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".  [TBD] 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.


6.  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 4.1 and Refs. 6 and 7.)

7.  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}:     ..................
     }

8.  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).


9.  References

[1] The Common Indexing Protocol:
    <URL:ftp://ds.internic.net/internet-drafts/draft-ietf-find-new-\
     cip-01.txt>

[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]  T. Berners-Lee, L. Masinter, and M. McCahill, Uniform Resource
     Locators (URL), RFC 1738, December 1994,
     <URL:http://ds.internic.net/rfc/rfc1738.txt>

[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, February 1997,
     <URL:ftp://ds.internic.net/internet-drafts/draft-kunze-dc-00.txt>

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

10.  Authors' Addresses

   Edward Hardie
   NASA Network Information Center
   MS 204-14
   Moffett Field, CA 94035-1000 USA
   +1 415 604  0134
   hardie@nasa.gov

   Mic Bowman
   Transarc Corporation
   The Gulf Tower
   707 Grant Street
   Pittsburgh, PA 15219 USA
   +1 412 338 4400
   mic@transarc.com

   Darren Hardy
   Netscape Communications Corp.
   685 E. Middlefield Road
   Mountain View, CA 94043 USA
   +1 415 937 2555
   dhardy@netscape.com

   Mike Schwartz
   @Home Network
   385 Ravendale Drive
   Mountain View, CA 94043 USA
   +1 415 944 7200
   schwartz@home.net

   Duane Wessels
   National Laboratory for Applied Network Research
   +1 303 497 1822
   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.
}