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Versions: 00 01 02 03

Network Working Group                                           J. Kunze
Internet-Draft                                California Digital Library
Intended status: Informational                                 N. Nassar
Expires: November 3, 2017                                 Index Data ApS
                                                             May 2, 2017


                  THUMP: The HTTP URL Mapping Protocol
                          draft-kunze-thump-03

Abstract

   The HTTP URL Mapping Protocol (THUMP) is a set of URL-based
   conventions for retrieving information and conducting searches.
   THUMP can be used for focused retrievals or for broad database
   queries.  A THUMP request is a URL containing a query string that
   starts with a `?', and can contain one or more THUMP commands.
   Returned records are formatted with Dublin Core Kernel metadata as
   Electronic Resource Citations, which are similar to blocks of email
   headers.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on November 3, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  A Sample THUMP Session  . . . . . . . . . . . . . . . . . . .   3
   3.  Keys and Citations  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Key-Request Dualism . . . . . . . . . . . . . . . . . . . . .   5
   5.  Request Summary . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Key ? help  . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Key ? was(DESCRIPTION) when(DATE) resync  . . . . . . . .   6
     5.3.  Key ? in(DB) find(QUERY) sort([!]ELEMS) list(RANGE)
           show(ELEMS) as(FORMAT)  . . . . . . . . . . . . . . . . .   7
     5.4.  Key ? . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.5.  Key ??  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.6.  Key ? get() put() group() apply() . . . . . . . . . . . .   9
   6.  Response Summary  . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Returned Records  . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Empty values for required elements  . . . . . . . . . . .  11
   8.  FAQ -- Frequently Asked Questions . . . . . . . . . . . . . .  12
     8.1.  What's the difference between THUMP, OpenSearch, SRU/SRW,
           and OpenURL?  . . . . . . . . . . . . . . . . . . . . . .  12
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Overview

   This document specifies The HTTP URL Mapping Protocol (THUMP), a set
   of URL-based conventions for retrieving information and conducting
   searches.  THUMP can be used for focused retrievals; e.g., for a
   given known-item, asking that a specifically formatted subset of
   information about it be returned.  It can also be used for broad
   database queries, such as finding all records matching the word,
   "monitor".

   A THUMP request is a URL containing a query string that starts with a
   `?', and can contain one or more THUMP commands.  A request is passed
   to a server with HTTP GET (or POST if desired).  The shortest request
   is a URL ending in `?', as in,

       http://example.com/object321?

   which asks the server to return a metadata record describing the
   information item identified by the URL.  This is a shorthand for the



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   common request for a short description of a known-item; the
   completely spelled out equivalent in this case would be

       http://example.com/object321?show(brief)as(anvl/erc)

   An example of a broad database search is,

       http://example.com/?in(books)find(war and peace)show(full)

   Query strings and responses are UTF8-encoded [RFC3629].  A THUMP
   response is an HTTP message body containing one or more records.
   Records contain Kernel metadata [Kernel] elements h1-h4.  The
   currently defined tag names are summarized below, formatted as
   Electronic Resource Citations (ERC), which are similar to blocks of
   email headers.  In an ERC each element consists of a label, colon,
   and value; long values are continued on indented lines and empty
   lines separate records.  It will be possible in a future version of
   THUMP to request ERC records formatted in XML.

2.  A Sample THUMP Session

   THUMP is very simple and follows the classical stateless HTTP
   communication model.  This section contains a complete annotated
   example of a request and response exchange.  To summarize, the
   requester sets up a TCP/HTTP session with the server system, sends a
   THUMP request inside an HTTP request, receives an answer inside an
   HTTP response, and closes the session.

   In the following example THUMP session, each line has been annotated
   to include a line number and whether it was the client or server that
   sent it.  Without going into depth, the session has four pieces
   separated by blank lines: the client's piece (lines 1-3), the
   server's HTTP/THUMP response headers (4-7), and the body of the
   server's response (8-18).  The first and last lines (1 and 18)
   correspond to the client's steps to start the TCP session and the
   server's steps to end it, respectively.  The heart of the request is
   the known-item metadata request indicated by the URL ending in a
   single `?' on line 2.













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    1  C: [opens session]
       C: GET http://ark.cdlib.org/ark:/13030/ft167nb0vq? HTTP/1.1
       C:
       S: HTTP/1.1 200 OK
    5  S: Content-Type: text/plain
       S: THUMP-Status: 0.6 200 OK
       S:
       S: erc:
       S: who:   Stanton A. Glantz and Edith D.  Balbach
   10  S: what:  Tobacco War: Inside the California Battles
       S: when:  20000510
       S: where: http://ark.cdlib.org/ark:/13030/ft167nb0vq
       S: [closes session]

   The first two server response lines (4-5) above are typical with
   HTTP.  The next line (6) is peculiar to THUMP, and indicates the
   THUMP version and a normal return status.  The balance of the
   response consists of a single metadata record (8-12) that comprises
   the service response.

   The returned record (8-12) in this case is in the ERC format (other
   formats are possible).  It contains four elements that answer high
   priority questions regarding an expression of the object: who played
   a major role in expressing it, what the expression was called, when
   is was created, and where the expression may be found.

3.  Keys and Citations

   A THUMP request is a command sequence operating on a Key, which is a
   base URL for a service point that supports THUMP.  It is expected,
   however, that the Key may generalize to service points in client-
   server computation contexts other than today's WWW.

   The Key uses a "citation-centered" system of reference.  This means
   that data elements are addressed relative to an abstract object
   surrogate, or "citation".

   While some systems have stored metadata-based surrogates (e.g.,
   library catalog records for books), many other systems do not.  This
   is not an obstacle to using THUMP.  The latter usually support the
   display or delivery of dynamically generated object citations, each
   consisting of such things as an access URL, a size, a date, a title,
   a snippet of relevant text (e.g., matching a query), plus links to
   related materials.

   Non-surrogate information objects in this model are, loosely
   speaking, the priority objects for end users, and include documents,
   articles, books, films, recordings, etc.  Surrogates, whether static



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   or dynamically generated, are important temporary stand-ins during
   discovery, filtering, and selection processes.  They are easy to
   manipulate in large numbers because they are much more homogeneous
   than the objects they represent.  Those objects are often too large,
   unwieldy, or rights-encumbered to be dealt with directly during
   discovery.  Surrogates are also valuable in preservation since they
   can provide useful information about the original context,
   dependencies, and provenance of an object.

4.  Key-Request Dualism

   Although THUMP does not specify anything about the structure of the
   Key, it is possible for a given Key string to express, often in an ad
   hoc manner, information similar to that expressed in the Request
   query string.  The more intuitive the Key structure, the greater the
   chance for it to carry information that might appear to repeat or
   even contradict commands in the Request.  For example, one server
   might require

       http://example.org/?in(books)find(war and peace)show(full)

   while another server required

       http://example.com/in=books/find=war+and+peace?show(full)

   and a third server required

       http://example.net/books/full/war_and_peace

   There is a natural dualism that servers may exploit by permitting or
   proposing (e.g., by returning) such semantically-laden Keys.  Any
   conventions for re-expressing THUMP commands within the Key or for
   resolving apparent contradictions, however, are up to individual
   servers and are out of scope for this document.

   This document recognizes the dualism but does not constrain it except
   to say that for a given Key, a server that declares THUMP support
   MUST respond to the "help" command by listing all the commands
   (methods) valid for that Key.  As a foundation requirement, the
   "help" command is a common way to ping a THUMP server to see if it is
   alive.  As an edge case, a THUMP response might be returned even for
   a URL that has no request at all (not even a `?'); this might make
   sense, for example, when the URL serves as the base Key for an entire
   service.

   There are cases when a server may wish to generate a temporary Key as
   a stand-in for a long or complex request and return it along with a
   subset of found records.  For example, the request,



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       http://example.com/?in(books)find(war and peace)list(10|1)

   might return the first 10 records along with a Key that could be used
   in subsequent requests to return the next 10 records:

       http://example.com/req98765?list(10|11)

   Note that this document makes no assumption about the dynamicity of
   queries, whether expressed partially or entirely in the Key or in the
   request.  In either form, returned records might come from cached
   results or from results freshly computed upon each access.  THUMP
   support does not constrain servers in this regard.

5.  Request Summary

   There are several request forms described below, with output formats
   listed in a later section.  Spaces have been inserted for readability
   in the forms below; usually, inter-command spaces would not be
   present.  It is normal to formulate THUMP queries using only a subset
   of the commands specified.  With a few important exceptions, this
   document is silent on how servers supply defaults or whether they
   signal errors for missing commands.  All default actions and server-
   side request modifications SHOULD be reported back to the client.

5.1.  Key ? help

   This form is required.  A server that declares THUMP support MUST
   respond to the "help" command by listing all the commands (methods)
   valid for that Key.  As a foundation requirement, the "help" command
   is a common way to ping a THUMP server to see if it is alive.

5.2.  Key ? was(DESCRIPTION) when(DATE) resync

   This "metadata" command form provides nothing more than a way to
   carry a Key along with its description.  The form is a "no-op"
   (except when "resync" is present) in the sense that the Key is
   treated as an adorned URL (as if no THUMP request were present).
   This form is designed as a passive data structrue that pairs a
   hyperlink with its metadata so that a formatted description might be
   surfaced by a client-side trigger event such as a "mouse-over".  It
   is passive in the sense that selecting ("clicking on") the URL should
   result in ordinary access via the Key-as-pure-link as if no THUMP
   request were present.  The form is effectively a metadata cache, and
   the DATE of last extraction tells how fresh it is.

   The "was" pseudo-command takes multiple arguments separated by "|",
   the first argument identifying the kind of DESCRIPTION that follows,
   e.g,



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   was(erc|Tolstoy, L|War and Peace|1863|http://example.org/etext/2600)

   The "when" pseudo-command (optional) takes one argument that is the
   date that the immediately DESCRIPTION was extracted.  The date,
   conforming to the [TEMPER] specification, looks like YYYYMMDDhhmmss.
   The "was" and "when" pseudo-commands can harmlessly accompany any
   THUMP request.

   The "resync" command, however, is a request to update the metadata.
   It returns a "metadata" form similar to the one submitted, but with
   refreshed metadata and no "resync" at the end.

5.3.  Key ? in(DB) find(QUERY) sort([!]ELEMS) list(RANGE) show(ELEMS)
      as(FORMAT)

   This form is used for generalized queries.  The server is permitted
   to modify commands, such as by supplying missing commands (defaults),
   but SHOULD report the resulting filled-out command xxx.

   *in(DB)*
   The "in" command specifies one or more dataset names separated by
   "|".  If no "in" command is present, the server picks a suitable
   default dataset or returns an error.  If no other commands are
   present, the server may treat the dataset as a result set or return
   an error.  Dataset names originating in relational databases are
   assumed to name a table in a default database, but may be structured
   into database, schema, and table names using the reserved characters
   '/' and '.' as per the following forms:

       database/schema.table
       database/table
       schema.table
       table

   *find(QUERY)*
   The "find" command specifies a QUERY that should produce a result set
   of matching records or an error.  The result set is modeled as a
   numbered sequence of records that is returned "by reference" with a
   generated Key (see the "results" tag later) or as one or more
   returned subsequences of records, known as returned sets.  If no
   "find" command is present, Key is expected to imply either a single
   record or a set of records.  THUMP distinguishes between a result set
   and a returned set, which is a subsequence of the result set included
   in a given response.

   The QUERY consists of free text words separated by spaces.  Reserved
   words begin with a ":" (colon), such as the :and, :or, and :not
   boolean operators.  Parentheses can be used for grouping.  Prepending



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   "+" ("-") to a word is done when the requester desires that the word
   be present (absent) from search results.  The double-quote character
   can be used to join words in a phrase or to turn off the special
   meanings of parentheses or ":+-" in front of words.

   *sort([!]ELEMS)*
   The "sort" command is used to request ordering according to the ELEMS
   specification (descending order if preceded by '!').  If no "sort"
   command is present, it is up to the server to determine record
   ordering.  ELEMS is one or more element or element subset names
   separated by "|".

   *list(RANGE)*
   The "list" command is used to request that a specific subsequence or
   RANGE of records be returned.  The server should always use the
   starting point of the requested RANGE, but is free to return fewer
   records (or a partial record).  In all cases the server must report
   what records or record fragment it has returned.  If no "list"
   command is present, it is up to the server whether to return records,
   and if so, which records.

   RANGE is a pair of arguments, "LENGTH|START", indicating the number
   of records and starting record in the requested sequence.  For
   example, a RANGE of "10|81" requests 10 records beginning with result
   set record 81.  If both arguments are missing, as in "list()", it is
   considered a request for all records.  If given as just "list(0)", it
   is a request that no records be returned directly, but a that the
   result set be returned by reference to a generated Key listed in the
   "results" tag of the returned set header.  If LENGTH is positive and
   START is 0, the server should send LENGTH randomly selected result
   set records.  If START is missing it defaults to 1; if LENGTH is
   missing, it is considered a request for all records starting from
   START.

   RANGE may also be used to request record fragments.  A returned
   record set consists of either one or more entire (whole) records, or
   of exactly one fragment of one record.  When a fragment is returned,
   the start position in the set header (described later) is indicated
   with S_F, where S is the record number and F is the fragment sequence
   number.  To request the next fragment, a START is formulated by
   adding 1 to F.  For example, "10|45_3" requests 10 records starting
   at fragment 3 of record 45 (only one fragment can be returned).

   *show(ELEMS)*
   The "show" command is used to request that returned records be
   constituted with ELEMS elements.  ELEMS is one or more element or
   element subset names separated by "|".  It can be used by users to




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   define the composition and element order of a returned record set;
   element names are discovered by XXX.

   Element subset names can also be used.  Common subset names are
   "brief", "full", and "support" (a record that is complete enough to
   show the server's commitment to the object.  If no "show" command is
   present, it is up to the server which elements to return.

   *as(FORMAT)*
   The "as" command is used to request that returned records be
   formatted according to FORMAT.  Common format names are "anvl/erc",
   "anvl/qdc", and "xml/marc".  If no "as" command is present, the
   default format is usually "anvl/erc" (a plain text format that is
   eye-readable and machine-readable), although a service may define
   defaults in its own way.

5.4.  Key ?

   This is a shorthand for

       Key ? show(brief) as(anvl/erc)

   which returns a brief object (identified by Key) description.
   Support for this shorthand is required.

5.5.  Key ??

   This is a shorthand for

       Key ? show(support) as(anvl/erc)

   which returns an object description full enough to contain the server
   provider's commitment statement.  Support for this shorthand is
   required.

5.6.  Key ? get() put() group() apply()

   These commands are currently undefined and reserved by THUMP for
   future use.

6.  Response Summary

   A THUMP response consists of a block of HTTP and extension headers, a
   blank line, and, if the THUMP-Status extension header was 200, a
   returned set of records.  The Content-Type HTTP header is normally
   returned as

       Content-Type: text/plain



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   so that the results will display correctly on a web browser's
   display.  The THUMP content types "text/xml" and "text/html" are
   being considered.

   The rest of this section describes the THUMP extension headers and
   the structure of the returned record set.  Extension headers are
   inserted in the block of HTTP response headers, usually near the end.
   Currently, one extension header, THUMP-Status, is defined, and it is
   required:

       THUMP-Status: THUMPVersion StatusCode ReasonPhrase

   It includes the version, a short human-readable phrase, and a 3-digit
   integer result code indicating the status of the attempt to execute
   the request.  Defined StatusCodes and ReasonPhrases for THUMP are:

       200: OK
       400: Bad Request
       402: Payment Required
       403: Forbidden
       404: Not Found
       405: Method Not Allowed
       408: Request Time-out

   If the status code is other than 200, no record set should be sent.
   If the server wishes to convey any more detailed diagnostic or error
   information than may be expressed by the above status codes, it MUST
   set the code to 200 and use "error" or "warning" element tags within
   the returned record set.

   A blank line separates the HTTP response and THUMP-Status headers
   from the returned set that is the body of the response.  The returned
   record set consists of a set-start header record followed by a
   sequence of records, each separated by one ore more blank lines,
   until end of stream (file) is reached.  A set-end header record is
   optional.

   The format of the records is normally "anvl/erc", which specifies a
   serialization syntax [ANVL] with ERC semantics [Kernel].  In a future
   version of THUMP it will be possible to request ERC semantics with
   "xml/erc".  The next sections describe the special ANVL record used
   to introduce a record set and then the ERC records.

7.  Returned Records

   This section describes how a record in the sequence of returned
   records is encoded in the anvl/erc format.  ANVL (A Name Value
   Language) defines the syntax and the ERC (Electronic Resource



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   Citation) defines semantics.  The URI for the ERC [Kernel] reference
   should be included in the record set header.  While a comprehensive
   description of the ERC record is out of scope for this document, some
   details are give below that may suffice for simple implementations.

   An ERC record is a sequence of tagged elements.  It has the form,

       erc:
       who:   WHO_EXPRESSED_THIS_ITEM
       what:  WHAT_THE_EXPRESSION_WAS_CALLED
       when:  WHEN_IT_WAS_EXPRESSED
       where: WHERE_THE_EXPRESSION_CAN_BE_FOUND
       how:   DESCRIPTION_OR_SUMMARY_OF_ITEM              <optional>
       why:   COPYRIGHT_DISCLAIMER_AUDIENCE_STATEMENT     <optional>
       note:  ANY_TEXT                                    <optional>
              .......
       <any other tagged elements>                        <optional>

   The first five tagged elements are required.  The required elements
   may be thought to answer questions about an "expression" of a
   resource (an item).

   All other elements are optional.  The next ERC element shown above
   ("how") is concerned with the content of an item and the element
   after that ("why") with any high priority information that comes from
   the lawyerly domain -- the really hard questions.

   A short form of the ERC is also possible that the above ordering for
   the first 6 elements.  It has the form,

       erc: WHO | WHAT | WHEN
            | WHERE
            | HOW                                         <optional>
            | WHY                                         <optional>
       note:  ANY_TEXT                                    <optional>
              .......
       <any other tagged elements>                        <optional>

   The line breaks among the first 6 elements are arbitrary.  Together
   they are considered to be part of one long value for the "erc:" as
   long as they are continued on indented lines.  In either form of the
   ERC, arbitrary additional elements are possible.

7.1.  Empty values for required elements

   Although they are required, if no suitable element value can be
   found, a controlled code value for "empty" of the form




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       (:ccode)

   should be used, drawing from the following reserved values:

      (:unac) temporarily inaccessible

      (:unal) unallowed, suppressed intentionally

      (:unap) not applicable, makes no sense

      (:unas) value unassigned (e.g., Untitled)

      (:unav) value unavailable, possibly unknown

      (:unkn) known to be unknown (e.g., Anonymous, Inconnue)

      (:none) never had a value, never will

      (:null) explicitly and meaningfully empty

      (:tba) to be assigned or announced later



      (:etal) too numerous to list (et alia).

      (:at) the real value is at the given URL or identifier.

8.  FAQ -- Frequently Asked Questions

8.1.  What's the difference between THUMP, OpenSearch, SRU/SRW, and
      OpenURL?

   All of these protocols are capable of expressing a parameter package
   on the right-hand side of a URL, and all of them reserve specific
   parameter names as having defined meanings.  In theory, these
   packages can be extended arbitrarily to express any functionality
   with any level of complexity.  There's no syntactic limitation to
   these protocols' expressiveness.  The difference lies in how.

   THUMP uses a classic parenthesized argument list syntax while the
   others use the flat argument-value list syntax traditional on the web
   since 1995.  OpenSearch and SRU/SRW are logical descendants of the
   complex Z39.50 search and retrieve protocol, but with restricted
   functionality and a text-based syntax.  SRW and OpenURL define an
   XML-encoding for request parameters.  OpenURL tends to be used for
   known-item linking.  THUMP aims to be a more concise specification
   for key-based requests.



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9.  Security Considerations

   The THUMP protocol poses no direct risk to computers and networks.
   Implementors of THUMP services need to be aware of security issues
   when querying networks and filesystems, and the concomitant risks
   from spoofing and obtaining incorrect information.  These risks are
   no greater for THUMP than for any other kind of HTTP-based
   application.  For example, recipients of a URL with embedded THUMP
   commands should treat it like a URL and be aware that the identified
   service may no longer be operational.

   THUMP clients and servers subject themselves to all the risks that
   accompany normal operation of the protocols underlying mapping
   services (e.g., HTTP, Z39.50).  As specializations of such protocols,
   a THUMP service may limit exposure to the usual risks.  Indeed, THUMP
   services may enhance a kind of security by helping users identify
   long-term reliable references to information objects.

10.  References

   [ANVL]     Kunze, J., Kahle, B., Masanes, J., and G. Mohr, "A Name-
              Value Language", August 2005,
              <http://www.cdlib.org/inside/diglib/ark/anvlspec.pdf>.

   [ARK]      Kunze, J. and R. Rodgers, "The ARK Persistent Identifier
              Scheme", July 2007,
              <http://www.cdlib.org/inside/diglib/ark/arkspec.pdf>.

   [Kernel]   Kunze, J. and A. Turner, "Kernel Metadata and Electronic
              Resource Citations (ERCs)", October 2007,
              <http://www.cdlib.org/inside/diglib/ark/ercspec.html>.

   [RFC2822]  Resnick, P., Ed., "Internet Message Format", RFC 2822,
              DOI 10.17487/RFC2822, April 2001,
              <http://www.rfc-editor.org/info/rfc2822>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <http://www.rfc-editor.org/info/rfc3629>.

   [RFC5013]  Kunze, J. and T. Baker, "The Dublin Core Metadata Element
              Set", RFC 5013, DOI 10.17487/RFC5013, August 2007,
              <http://www.rfc-editor.org/info/rfc5013>.








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Internet-Draft                    THUMP                         May 2017


Authors' Addresses

   John Kunze
   California Digital Library
   415 20th St, #406
   Oakland, CA  94612
   USA

   Email: jak@ucop.edu


   Nassib Nassar
   Index Data ApS
   Njalsgade 76, 13
   Copenhagen  2300
   Denmark

   Email: nassib@indexdata.com

































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