A Persistent Web IDentifier (PWID) URN Namespace
draft-pwid-urn-specification-06

Document Type Active Internet-Draft (individual)
Last updated 2019-03-01
Stream (None)
Intended RFC status (None)
Formats plain text xml pdf html bibtex
Stream Stream state (No stream defined)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date
Responsible AD (None)
Send notices to (None)
Internet Engineering Task Force                           E. Zierau, Ed.
Internet-Draft                                      Royal Danish Library
Intended status: Informational                             March 1, 2019
Expires: September 2, 2019

            A Persistent Web IDentifier (PWID) URN Namespace
                    draft-pwid-urn-specification-06

Abstract

   This document specifies a Uniform Resource Name (URN) for Persistent
   Web IDentifiers for web material in web archives using the 'pwid'
   namespace identifier.

   The main purpose of the standard is to support specification of
   references that are not covered by other reference techniques: to
   support references to material in web archives with restricted
   access.  Furthermore, it supports persistent technology agnostic
   references to web archives in general, in a form that can work as an
   algorithmic basis for finding web archive resources in general.  An
   additional important benefit is that the standard can be used for
   specifying web collections, which can then form a persistent
   computational basis for the extract of the archived collection parts.
   Since these parts can be specified generally, this further allows
   collections to be specified with elements from one or more web
   archives.

   The PWID URN is designed to meet requirements for proper referencing
   needed by researchers.  Therefore it is designed as general, global,
   sustainable, humanly readable, technology agnostic, persistent and
   precise web references for web materials in web archives.

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 https://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."

Zierau                  Expires September 2, 2019               [Page 1]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

   This Internet-Draft will expire on September 2, 2019.

Copyright Notice

   Copyright (c) 2019 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
   (https://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
   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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Namespace Registration Template . . . . . . . . . . . . . . .   6
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     4.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   The PWID URN is a supplement to existing reference standards, where
   the PWID URN will support references to web archives, including areas
   that are not supported today: support of references to material in
   web archives with restricted access.  Furthermore, the PWID URN
   enables technology agnostic references to web archives in general,
   which can be needed, for instance for references to dynamic web
   material with frequent updates (e.g. a news site) or a specific
   version of a web material (e.g. specific version of the DOI
   handbook).

   The PWID URN is in a form which can work as an algorithmic basis for
   finding the resource.  This also enables computation of archived web
   parts to a collection from one or more web archives, if the
   collection parts are specified by PWID URNs.

   Furthermore, the PWID URN includes information about the resource
   which makes it possible to find alternative resources, in cases where
   the original precise resource has become unavailable.

Zierau                  Expires September 2, 2019               [Page 2]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

   The PWID URN is designed to be a persistent reference that is
   general, global and technology agnostic in order to enhance its
   chances of being sustainable.  Furthermore, it is designed to be
   humanly readable and with an ability to specify precision about what
   the referenced web archive resource covers.  This design enables a
   PWID URN to:

   o  be used in technical solutions, e.g. to make them resolvable

   o  cover references to all sorts of materials in web archives

   o  cover references to materials from all sorts of web archives

   The motivation for defining a PWID namespace is the growing
   challenges of references to archived web resources, and the PWID as a
   URN can assist in overcoming a lot of these challenges.  The standard
   is needed to address web materials meeting precision and persistency
   issues on par precision in traditional references for analogue
   material.  Furthermore, it is needed in order to address web archive
   resources that are not freely available online.  The PWID URN covers
   both referencing of web resources from research papers and definition
   of web collections/corpora.  In detail the challenges are:

   o  Persistent Identifier systems (like DOI [DOI]) will only cover
      registered resources.  In general, citation guidelines do not
      cover general and persistent referencing techniques for web
      resources that are not registered.  However, an increasing number
      of references point to resources that only exist on the web, e.g.
      blogs that turn out to have a historical impact.  In order to
      obtain persistency for a reference, the target needs to be stable.
      For non-registered web resources, the common rule is that the
      resource will change, since the live-web is constantly changing.
      Persistency can only be obtained by referring to something stable,
      i.e. an archived snapshot of the resource from the web.  The PWID
      URN is therefore focused on referencing archived web material in a
      technology agnostic way (research documented in [IPRES2016] and
      [ResawRef]).

   o  References to materials, which only exist in web archives (i.e. no
      longer on the live web) are not well supported, especially not for
      materials that only exists in archives with restricted access.
      There are many new initiatives for web archive referencing, - most
      of which are centralized solutions offering harvesting and
      referencing, but these cannot be used for materials that only
      exist in web archives.  The PWID URN can be used for all web
      archives, including web archives with restricted access.

Zierau                  Expires September 2, 2019               [Page 3]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

   o  One of the referencing initiatives for open web archives uses URLs
      which depend on the current setup of the web archive's access
      platform.  These URLs are usually technology and placement
      dependent, and therefore such a reference style is not suited for
      references that are important to retrace for a long period.  The
      PWID URN can be used for such reference purposes, since it is
      technology agnostic.

   o  Another referencing initiative, for open web archives, is omitting
      specification of the web archive where the resource was found.
      This strategy is used in order to open the possibility of using
      alternatives from other archives.  However, this also adds a risk
      of imprecision since different archives tend to have different
      versions even when harvesting at the same time.  Therefore, such a
      reference style is not suited for references where it is important
      that the reference is precisely the verified reference.  The PWID
      URN can provide an exact reference for where the reference was
      validated.  Additionally, the PWID contains the needed information
      in order to search for alternative resource, if needed.

   o  For reference of web collections/corpora (possibly across
      different web archives), recent research have found that various
      legal and sustainability issues has led to a need of a collection
      definition of references to their web parts.  Furthermore, there
      is a need for a similar persistent referencing for all parts for
      calculation and sustainability reasons.  So far, there has been no
      stable standard for definition of such collection parts.  The PWID
      URN can be used for such definitions in order to fulfil these
      requirements (research documented in [ResawColl]).

   The PWID URN is especially useful for web material where precision is
   in focus and/or there are references to materials from web archives
   requiring special permissions in order to gain access.  The precision
   regards both pointing to the archive where it was found and validated
   against its purpose (other archived versions in other web archives
   may differ both regarding completeness and contents even within short
   time periods) as well as precision in what is actually referred by
   the reference (e.g. is it the page or the whole website).

   Furthermore, the PWID URN is very useful in specification of contents
   of a web collection.  Definitions of web collections are often needed
   for extraction of data used in production of research results, e.g.
   for future evaluations.  Current practices are not persistent as they
   often use some CDX version, which vary for different implementations.

   Strict syntax is needed for the PWID URN, in order to ensure that it
   can act as a reference which can used for computational purposes.
   This is especially relevant for automatic extraction of parts from

Zierau                  Expires September 2, 2019               [Page 4]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

   web collection definitions.  Furthermore, today's readers of research
   papers are expecting to be able to access a referenced resource by
   clicking an actionable URI, therefore a similar possibility will be
   expected for references to available archived web material, and this
   is possible with a strict syntax.  Examples of technical solutions
   that are enabled are:

   o  Resolving of a reference to a web collection and automatic
      extraction of the parts of a web collection defined by PWID URNs
      [ResawRef] [ResawColl]

   o  Resolving of a PWID URN by resolving services.  To begin with, a
      prototype has been developed for the Danish web archive data and
      open web archives with standard patterns for the current
      technologies.  Implementations for resolution of PWID URNs for
      other web archives may be developed.

   The purpose of the PWID URN is also to express a web archive
   reference as simple as possible and at the same time meet the
   requirements for sustainability, usability and scope.  Therefore, the
   PWID URN is focused on having only the minimum required information
   to make a precise identification of a resource in an arbitrary web
   archive.  Recent research have shown that this can be obtained by the
   following information [ResawRef]:

   o  Identification of web archive

   o  Identification of source:

      *  Archived URI or identifier

      *  Archival timestamp

   o  Intended precision (page, part, subsite etc.)

   The PWID URN represents this information in a human readable way as
   well as a well-defined way that enables technical solutions to
   interpret the URN.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

Zierau                  Expires September 2, 2019               [Page 5]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

2.  Namespace Registration Template

   Namespace Identifier:

      PWID

   Version:

      6

   Date:

      2019-03-01

   Registrant:

      Eld Maj-Britt Olmuetz Zierau
      Royal Danish Library
      Soeren Kierkegaards Plads 1
      1219 Copenhagen
      Denmark
      ph: +45 9132 4690
      email: elzi@kb.dk

   Purpose:

      The PWID URN is a supplement to existing reference standards,
      where the PWID URN will support references to web archives,
      including areas that are not supported today: support of
      references to material in web archives with restricted access.
      Furthermore, the PWID URN enables technology agnostic references
      to web archives in general, which can be needed, for instance for
      references to dynamic web material with frequent updates (e.g. a
      news site) or a specific version of a web material (e.g. specific
      version of the DOI handbook).

      The PWID URN is in a form which can work as an algorithmic basis
      for finding the resource.  This also enables computation of
      archived web parts to a collection from one or more web archives,
      if the collection parts are specified by PWID URNs.

      Furthermore, the PWID URN includes information about the resource
      which makes it possible to find alternative resources, in cases
      where the original precise resource has become unavailable.

      The PWID URN is designed to be a persistent reference that is
      general, global and technology agnostic in order to enhance its

Zierau                  Expires September 2, 2019               [Page 6]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

      chances of being sustainable.  Furthermore, it is designed to be
      humanly readable and with an ability to specify precision about
      what the referenced web archive resource covers.  This design
      enables a PWID URN to:

      *  be used in technical solutions, e.g. to make them resolvable

      *  cover references to all sorts of materials in web archives

      *  cover references to materials from all sorts of web archives

      The motivation for defining a PWID namespace is the growing
      challenges of references to archived web resources, and the PWID
      as a URN can assist in overcoming a lot of these challenges.  The
      standard is needed to address web materials meeting precision and
      persistency issues on par with precision in traditional references
      for analogue material.  Furthermore, it is needed in order to
      address web archive resources that are not freely available
      online.  The PWID URN covers both referencing of web resources
      from research papers and definition of web collections/corpora.
      In detail the challenges are:

      *  Persistent Identifier systems (like DOI [DOI]) will only cover
         registered resources.  In general, citation guidelines do not
         cover general and persistent referencing techniques for web
         resources that are not registered.  However, an increasing
         number of references point to resources that only exist on the
         web, e.g. blogs that turn out to have a historical impact.  In
         order to obtain persistency for a reference, the target needs
         to be stable.  For non-registered web resources, the common
         rule is that the resource will change, since the live-web is
         constantly changing.  Persistency can only be obtained by
         referring to something stable, i.e. an archived snapshot of the
         resource from the web.  The PWID URN is therefore focused on
         referencing archived web material in a technology agnostic way
         (research documented in [IPRES2016] and [ResawRef]).

      *  References to materials, which only exist in web archives (i.e.
         no longer on the live web) are not well supported, especially
         not for materials that only exists in archives with restricted
         access.  There are many new initiatives for web archive
         referencing, - most of which are centralized solutions offering
         harvesting and referencing, but these cannot be used for
         materials that only exist in web archives.  The PWID URN can be
         used for all web archives, including web archives with
         restricted access.

Zierau                  Expires September 2, 2019               [Page 7]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

      *  One of the referencing initiatives for open web archives uses
         URLs which depend on the current setup of the web archive's
         access platform.  These URLs are usually technology and
         placement dependent, and therefore such a reference style is
         not suited for references that are important to retrace for a
         long period.  The PWID URN can be used for such reference
         purposes, since it is technology agnostic.

      *  Another referencing initiative, for open web archives, is
         omitting specification of the web archive where the resource
         was found.  This strategy is used in order to open the
         possibility of using alternatives from other archives.
         However, this also adds a risk of imprecision since different
         archives tend to have different versions even when harvesting
         at the same time.  Therefore, such a reference style is not
         suited for references where it is important that the reference
         is precisely the verified reference.  The PWID URN can provide
         an exact reference for where the reference was validated.
         Additionally, the PWID contains the needed information in order
         to search for alternative resource, if needed.

      *  For reference of web collections/corpora (possibly across
         different web archives), recent research have found that
         various legal and sustainability issues has led to a need of a
         collection definition of references to their web parts.
         Furthermore, there is a need for a similar persistent
         referencing for all parts for calculation and sustainability
         reasons.  So far, there has been no stable standard for
         definition of such collection parts.  The PWID URN can be used
         for such definitions in order to fulfil these requirements
         (research documented in [ResawColl]).

      The PWID URN is especially useful for web material where precision
      is in focus and/or there are references to materials from web
      archives requiring special permissions in order to gain access.
      The precision regards both pointing to the archive where it was
      found and validated against its purpose (other archived versions
      in other web archives may differ both regarding completeness and
      contents even within short time periods) as well as precision in
      what is actually referred by the reference (e.g. is it the page or
      the whole website).

      Furthermore, the PWID URN is very useful in specification of
      contents of a web collection.  Definitions of web collections are
      often needed for extraction of data used in production of research
      results, e.g. for future evaluations.  Current practices are not
      persistent as they often use some CDX version, which vary for
      different implementations.

Zierau                  Expires September 2, 2019               [Page 8]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

      Strict syntax is needed for the PWID URN, in order to ensure that
      it can act as a reference which can used for computational
      purposes.  This is especially relevant for automatic extraction of
      parts from web collection definitions.  Furthermore, today's
      readers of research papers are expecting to be able to access a
      referenced resource by clicking an actionable URI, therefore a
      similar possibility will be expected for references to available
      archived web material, and this is possible with a strict syntax.
      Examples of technical solutions that are enabled are:

      *  Resolving of a reference to a web collection and automatic
         extraction of the parts of a web collection defined by PWID
         URNs [ResawRef] [ResawColl]

      *  Resolving of a PWID URN by resolving services.  To begin with,
         a prototype has been developed for the Danish web archive data
         and open web archives with standard patterns for the current
         technologies.  Implementations for resolution of PWID URNs for
         other web archives may be developed.

      The purpose of the PWID URN is also to express a web archive
      reference as simple as possible and at the same time meet the
      requirements for sustainability, usability and scope.  Therefore,
      the PWID URN is focused on having only the minimum required
      information to make a precise identification of a resource in an
      arbitrary web archive.  Recent research have shown that this can
      be obtained by the following information [ResawRef]:

      *  Identification of web archive

      *  Identification of source:

         +  Archived URI or identifier

         +  Archival timestamp

      *  Intended precision (page, part, subsite etc.)

      The PWID URN represents this information in a human readable way
      as well as a well-defined way that enables technical solutions to
      interpret the URN.

   Syntax:

      The syntax of the PWID URN is specified below in Augmented Backus-
      Naur Form (ABNF) [RFC5234] and conforms to URN syntax defined in
      [RFC8141].  The syntax definition of the PWID URN is:

Zierau                  Expires September 2, 2019               [Page 9]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

        pwid-urn = "urn" ":" pwid-NID ":" pwid-NSS

        pwid-NID = "pwid"
        pwid-NSS = archive-id ":" archival-time ":" precision-spec
                              ":" archived-item-id

        archive-id = domain / "~" registered-archive-id
        registered-archive-id = +( unreserved )

        archival-time = utc-date ["T" utc-time] "Z"
        utc-date   = utc-year "-" utc-month "-" utc-day
        utc-year   = 4DIGIT
        utc-month  = 2DIGIT  ; 01-12
        utc-day    = 2DIGIT  ; 01-28, 01-29, 01-30, 01-31 based on
                         ; month/year in UTC time
        utc-time   = utc-hour ":" utc-minute [":" utc-second [secfrac]]
        utc-hour   = 2DIGIT  ; 00-23
        utc-minute = 2DIGIT  ; 00-59
        utc-second = 2DIGIT  ; 00-58, 00-59, 00-60 based on leap second
                                   ; rules
        secfrac       = "." (1-9)*DIGIT

        precision-spec = "part" / "page" / "subsite" / "site"
                 / "collection" / "recording" / "snapshot"
                 / extension
        extension = +( letter )

        archived-item-id = URI / "~" registered-item-id
        registered-item-id = +( unreserved )

      where

      *  All parts of the pwid-NSS are case insensitive, except for
         archived-item-id in cases where the archived-item-id is an URI
         with case sensitive parts.  According to [RFC8141] (section
         3.1) this means that the PWID URNs in general are case
         insensitive, except from cases where it includes a case
         sensitive URI as archived-item-id.

      *  archive-id must either be the domain for the archive which can
         lead to descriptions of how to access (or apply for access)
         materials in he archive, - or it must be a registered archive-
         id (registry still to be defined and created).  Distinction
         between the to types of identifiers is made by matching the
         first character with "~".  In case of a match, it means that
         the rest of the identifier is a registered archive item
         identifiers, since the syntax requires such identifiers to be

Zierau                  Expires September 2, 2019              [Page 10]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

         prefixed with "~", while no URI is allowed to start with this
         character

      *  'domain' is defined as in (section section 3.5) [RFC1034].

      *  'unreserved' is defined as in [RFC3986].

      *  'archival-time' is a UTC timestamp which conforms to the W3C
         profile of [ISO8601] [W3CDTF] and a subset of date-time
         specified in [RFC3339] (except from allowing partial time
         specification).  The archival-time may be specified at any of
         the levels of granularity, as long as it reflects exactly the
         granularity of the timestamp recorded in the archive (which is
         in accordance with the WARC standard [ISO28500]).

      *  archive-item-id must either be the archived URI for the source
         or a registered archive-item-id.  Distinction between the to
         types of identifiers is made by matching the first character
         with "~".  In case of a match, it means that the rest of the
         identifier is a registered archive item identifiers, since the
         syntax requires such identifiers to be prefixed with "~", while
         no URI is allowed to start with this character

      *  'URI' is defined as in [RFC3986] but where occurrences of "[",
         "]", "?", "#" and "%" are %-encoded in order not to clash with
         URN reserved characters [RFC8141] as well as having unambiguous
         use of "%".

      The precision specification is expressing the intended precision
      of the reference.  For example, if it refers to an html web
      element, this element can be interpreted in several ways:

      *  As one web part only
         Meaning the file containing the html, and precisely this file

      *  As a web page
         Meaning that an application like Wayback shows a resulting web
         page in a browser based on calculated referenced web parts
         (display templates, images etc.).
         If the full reference contains only the PWID URN for the page,
         this may mean that the archived page can change its appearance
         over time, e.g. if parts referred by the page did not exist at
         reference time, but are harvested at a later stage, - or if the
         web archive's algorithm for calculation of the referred web
         parts are changed and consequently returns a different result.
         Therefore, the most a precise reference to a picture in context
         of a web page would be to provide the PWID URN for the page

Zierau                  Expires September 2, 2019              [Page 11]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

         (with page precision) and the PWID URN for the image file part
         which contains the referred picture (with part precision)

      *  As a site or subsite
         Meaning that an application like Wayback shows the result in a
         browser showing the web page.  If access is limited to the
         referenced part (the html page), then the application would
         also need to make sure that all parts/pages belonging to the
         site/subsite is available.
         If the full reference only contains the PWID URN for the site/
         subsite, this may mean that the site/subsite can change its
         appearance over time in the same way as for the web page
         described above

      The precision specification needs to be part of a PWID URN in
      order to enable the making of the above described precision in the
      reference.  Furthermore, this precision specification will make it
      possible for resolvers to display the referred source in a way
      that corresponds to the precision specification.

      There are different ways to represent e.g. a web page, which
      provides different precision of the source as well.  The above
      examples with part, page, subsite and site are addressing the most
      common access via browser functionality like in Wayback.  However,
      some web archives archive snapshots of the web pages for the
      archived URI.  A third option is to produce a collection of
      archived URIs as basis for browser access instead of letting the
      web archive calculate sub items (which may change over time).  An
      example of the production of such a collection is provided in the
      section about assignment.  Lastly, a web page may be archived via
      a web recording.

      Because of the above, the following valid precision-spec values
      are exists:

      *  part
         The single archived web part harvested as a file from the
         specified URI, e.g. a pdf, an html text or an image

      *  page
         The web page represented by the web page file (e.g. html)
         harvested from the specified URI, where its content is
         interpreted as a web page with all referred parts relevant to
         display the web page (but where referred parts must be
         calculated as described above), e.g. an html page with referred
         images

      *  subsite

Zierau                  Expires September 2, 2019              [Page 12]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

         The referred web page (as described under 'page') from which is
         possible to browse to all references starting with the same
         path as the archived URI

      *  site
         The referred web page (as described under 'page') from which is
         possible to browse to all references in the domain specified in
         the archived URI

      *  collection
         Representation of a collection specification, where the web
         archive applications will decide how it is rendered (e.g.
         collection specification in the XML format enabling
         interpretation as in the example provided in [ResawColl])

      *  snapshot
         A snapshot (image) representation of web material, e.g. a web
         page

      *  recording
         Representation of a web recording specification where ithe web
         archive applications will decide how it is rendered
         (interpretation could e.g. depend on file-suffix for the web
         recording), an example is a web recording coded in a WARC file

      The option of making an extension value is included to allow
      reference of a resource of any kind with an assigned identifier,
      even if it is not covered by the other values.  In all cases, it
      will be up to the application serving the web archive to interpret
      how this item should be rendered.

   Assignment:

      The PWID URNs do not have to be assigned by an authority, as they
      are based on the information created at the time of archiving.  In
      other words: a PWID URN is created independently, but following an
      algorithm which ensures that the referred item can be found if it
      is still available.  A PWID URN also has the benefit that it
      includes information to look at alternative resources e.g. via
      Memento for some open web archives [MEMENTO] or via possible
      future web archive infrastructures.

      A PWID URN is created by finding the relevant information of the
      syntax parts of the PWID:

        "urn:pwid:" archive-id ":" archival-time ":" precision-spec
                               ":" archived-item-id

Zierau                  Expires September 2, 2019              [Page 13]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

      The PWID URN for an archived item at hand can be constructed by
      exchanging the unspecified PWID parts with relevant information,
      as explained in the following:

      *  archive-id (identification of web archive):
         In this version of the standard, it is recommended to use the
         domain of the web archive as the identifier for the web archive
         (e.g. archive.org for Internet Archive's open web archive and
         netarkivet.dk for the Danish web archive with restricted
         access).  This is recommended, since browsing the domain page
         will typically lead to a description of how to access the web
         archive, e.g. by online access or by applying for access
         grants.  Furthermore, it is more precise than e.g.  the name of
         the archive, since there may be more than one installation of
         web archives at the same organization, e.g.  archive.org and
         archive-it.org are both covered by Internet Archive.
         When a registry of web archives is established, it will be more
         precise and persistent to use the web archive identifier
         specified in this registry.  (e.g.  DKWA for the Danish web
         archive with the domain netarkivet.dk).  The syntax requires
         that such identifiers are prefixed with the charecter "~".

      *  archival-time (archival timestamp):
         The archival time for the archived item must be specified with
         as much granularity as possible in order to make sure it
         uniquely identifies the resourceat at hand.  The archival time
         may be displayed along with the archived item, but there are
         different implementations where it is important to be aware of
         whether a more precise timestamp can be found, and whether the
         correct timestamp is used.  In many Wayback implementations,
         the precise timestamp can be found as part of the URI used for
         viewing the archived item.  For example, the archive http URI
         https://web.archive.org/web/20160122112029/http://www.dr.dk for
         an archived resource viewable via the Internet Archive's
         Wayback installation, the number 20160122112029 represents the
         archival time 2016-01-22T11:20:29Z.  In other installations,
         the most precise timestamp may be found in the URI from a
         search result leading to the resource (which usually redirects
         on basis of a call to the underlying archive index).
         Especially for web pages with frames, there may be cases where
         the actual time is not displayed with the source, since only
         the times for the contents of the frames are displayed.

      *  precision-spec (precision as represented page, part, site,
         snapshot etc.):
         The precision specification specifies how the user should view
         the referred item - either as a specific representation (with
         inherited precision) or by use of tools (e.g. browse web site

Zierau                  Expires September 2, 2019              [Page 14]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

         based on calculations or browse on basis of collection of
         specific parts).
         Inherited precision is implicitly indicated by the precision
         specification from how the information is used in resolution
         and location.  The most precis reference is part, e.g. for an
         image which can be located and accessed independently.  Less
         precise references are references where calculation of other
         parts are needed in order to resolve and view it, e.g. page,
         site or subsite.

      *  archived-item-id (archived URI or registered identifier):
         The archived item identifier will either be the archived URI of
         the displayed archived item at hand, or it will be an
         identifier assigned for a resource by the archive.  In the
         latter case, the syntax requires that such identifiers are
         prefixed with the charecter "~".

      A much easier way to construct PWID URNs is to use tools that
      construct them.  Currently, there is also a prototype for a SOLR-
      Wayback tool (Source at https://github.com/netarchivesuite/
      solrwayback) [PWIDprovider], which can assist in finding the most
      precise reference to an archived web page.  This Wayback version
      can provide all PWID URNs belonging to a shown page (with the page
      PWID URN at the top).  For example, in netarkivet.dk, the archived
      URI for the web page http://www.susanlegetoej.dk/shop/handskedyr-
      siameser-killing-8681p.html archived 2008-11-29 01:19:16 UTC, has
      the following parts calculated by the SOLR-Wayback tool:

         urn:pwid:netarkivet.dk:2008-11-
         29T00:41:42Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_Master_NF.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:39:47Z:part:http://www.susanlegetoej.dk/shop/css/
         print.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:40:06Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_Basket_NF.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:40:00Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_TopMenu_NF.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:40:00Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_SearchPage_NF.css

Zierau                  Expires September 2, 2019              [Page 15]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

         urn:pwid:netarkivet.dk:2008-11-
         29T00:40:35Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_Productmenu_NF.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:40:22Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_SpaceTop_NF.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:40:24Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_SpaceLeft_NF.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:40:23Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_SpaceBottom_NF.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:40:25Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_SpaceRight_NF.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:37:23Z:part:http://www.susanlegetoej.dk/images/ddcss/
         SK113_ProductInfo_NF.css

         urn:pwid:netarkivet.dk:2008-11-
         29T00:37:24Z:part:http://www.susanlegetoej.dk/Shop/js/
         Variants.js

         urn:pwid:netarkivet.dk:2009-03-
         03T11:53:00Z:part:http://www.susanlegetoej.dk/Shop/js/Media.js

         urn:pwid:netarkivet.dk:2009-03-
         03T11:53:02Z:part:http://www.susanlegetoej.dk/images/design/
         print.gif

         urn:pwid:netarkivet.dk:2009-03-
         03T11:54:19Z:part:http://www.susanlegetoej.dk/Shop/js/Scroll.js

         urn:pwid:netarkivet.dk:2009-03-
         03T11:54:09Z:part:http://www.susanlegetoej.dk/Shop/js/
         Shop5Common.js

         urn:pwid:netarkivet.dk:2006-11-
         20T20:16:03Z:part:http://www.susanlegetoej.dk/images/602551.jpg

   Security and Privacy:

Zierau                  Expires September 2, 2019              [Page 16]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

      Security and privacy considerations are restricted to accessible
      web resources in web archives.  Resolvers to PWID URNs will
      usually only be possible using the web archives' access tools,
      where security and privacy are covered by these tools.  In such
      cases security and privacy will covered by such tools, since the
      information used for access has no security and privacy issues.
      In the cases where resolution is made around the archives' access
      tools, there should be made separate analysis.

   Interoperability:

      This is covered by comments in the Syntax description:

      *  the PWID URN conforms to the URI standard defined as in
         [RFC3986] and the URN standard [RFC8141]

      *  the 'archival-time' of the PWID URN conforms to the UTC
         timestamp as described in the W3C profile of ISO 8601 [ISO8601]
         [W3CDTF] and is in accordance with the WARC standard ISO 28500
         [ISO28500].

      *  for use of URIs for the 'archived-item-id', this URI conforms
         to the URI standard defined as in [RFC3986], with %-encodings
         of "[", "]", "#", "?" and "%" in order to conform to the URN
         standard [RFC8141] as well as having unambiguous use of "%"

   Resolution:

      The information in a PWID URN can be used for locating a web
      archive resource, for any kind of web archive.  It includes the
      minimum information for web archive materials, which enables
      resolvability, manually or by a resolver.  Resolution of a PWID
      URN is the primary motivation of making a formal URN definition,
      instead of just textual representation of the for needed parts of
      a PWID.

      Resolution (manually or automatically) is done based on the PWID
      parts:

      *  Web archive identification for web archive holding referred
         resource
         If the identifier do not start with "~", then the identifier is
         the domain name for the web archive, where browsing this domain
         page typically will lead to description of how to access the
         web archive.  For example, "archive.org" is the domain name
         leading to the Internet Archive's interface to their online web
         collection, and "netarkivet.dk" is the domain name leading to
         the website for the Danish web archive with information about

Zierau                  Expires September 2, 2019              [Page 17]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

         how to apply for access permission to the web collections.  If
         the identifier starts with "~" the archive can be identified by
         looking up the identifier (from the rest of the archive
         identier) in a registry of archives.  It is a future
         possibility is to have such a registry which should have
         archive identifiers along with their current location on the
         internet.  Such a registry will be needed for persistent
         reference to the archive, since an archive may change their
         location and name or archives may merge.  There is work in
         progress to define such a registry, but no details yet.

      *  Archived URI or registered identifier of archived item
         If the identifier do not start with "~", then the resource is
         an archived URI, this URI must be used in search for or
         construction of location of the resource.  If the identifier
         starts with "~", then the rest of the characters in the
         identifier constitutes a registered identifier assigned to the
         resource (by the archive), it is then this identifier that must
         be used in search for or construction of location of the
         resource

      *  Date and time associated with the archived item
         The archival date and time must be used in search for or
         construction of the location of the resource

      *  Precision of what is referred
         The precision can either contribute to the guidance of
         activating tools to view the referred item e.g. browse the
         referred item as a page on basis of computed closest past,
         browse the referred item on basis of parts specified in a
         collection, or view the referred item as a snapshot.  In the
         example of the snapshot, it also contains a specification of
         which resource to display

      In the following the different resolution techniques are explained
      (manual as well as via a service) .

      An example of a PWID URN is:

         urn:pwid:archive.org:2016-01-22T11:20:29Z:page:http://www.dr.dk

      has the information:

      *  archive.org
         Currently known identifier in form of the Internet Archive
         domain name for their open access web archive.  If Internet
         Archive registered their open web archive in an IANA web
         archive register, this identifier could currently be

Zierau                  Expires September 2, 2019              [Page 18]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

         "web.archive.org/web/" for Wayback resolution, or it could be
         "archive.org/pwid/" if a PWID interface was created as
         described below

      *  2016-01-22T11:20:29Z
         UTC date and time associated with the archived URI

      *  page
         Clarification that the reference cover the full web page with
         all its inherited parts selected by the web archive

      *  http://www.dr.dk
         archived URI of item

      Resolution of this URN PWID can be deduced based on the current
      (2019) knowledge of Internet Archive's open Wayback access web
      interface, which has the pattern:

         https://web.archive.org/web/<time>/<uri>

      Using this pattern (where only digits from the timestamp is
      included) it is possible manually (or automatically) to deduce the
      online https URI:

         https://web.archive.org/web/20160122112029/http://www.dr.dk

      The same recipe can be used for other Wayback platforms for open
      web archives.

      Another manual resolution is to find the resource by use of the
      specified web archive's search interface.  This will work for both
      open web archives and web archives with restricted access onsite.

      It is also noteworthy that the information in the PWID can help in
      finding an alternative resource, in case the original referred
      resource is no longer available.  The archived URI can be searched
      in other web archives, where the date and time can help to find
      the best match, e.g. via Memento (for some open web archives) or
      via possible coming web archive infrastructures.

      If an open web archive has registered an identifier for the web
      archive along with the current pattern for access with <time> and
      <uri> - and where the latter information is updated when the
      pattern change - then such a register can be used to deduce
      location on long term.  Likewise, for web archives with restricted
      access, the registry will be able to provide information of where
      to apply for access permissions.

Zierau                  Expires September 2, 2019              [Page 19]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

      Regarding the precision specification, there are so far no
      implementations which support distinctive rendering depending on
      such a parameter, e.g. only providing html for an html page
      specified as part and the page with calculated elements if
      specified as page etc.  Therefore, the precision specification
      will initially be ignored by a resolution to a Wayback interface.

      A resolving service is currently available in form of code for a
      prototype which run at the Royal Danish Library [PWIDresolver] and
      is planned to be more widely available.  This service currently
      covers both the Danish web archive (with the proper rights) and
      open web archives with access services based on a pattern
      including archive, archival time and archived URI.  In other
      words, for open web archives it covers conversion of PWID URNs
      for: archive.org, archive-it.org, arquivo.pt, bibalex.org,
      nationalarchives.gov.uk, stanford.edu and vefsafn.is.  For the
      Danish web archive with restricted access, the prototype works
      locally accessing the CDX of the library, and providing access via
      a local proxy to a restricted environment.  The source code for
      this prototype is available from
      https://github.com/netarchivesuite/NAS-research/releases/
      tag/0.0.6.

      Automatic access of a referenced web resource may work on the open
      web for open web archives or in restricted environments for the
      web archives with restricted access.  There may be a need for
      varied operation depending on the available technology and
      applications, e.g.:

      *  Via locally installed browser plug-ins or applications forming
         http/https URIs as described above

      *  Via web research infrastructures
         This is a future solution scenario as a web archive research
         infrastructure does not yet exist.  However, it is a likely
         future scenario, as it is currently being proposed in the RESAW
         community [RESAW]

   Documentation:

      None relevant

   Additional Information:

      The PWID was originally suggested as a URI, based on research
      between a computer science researcher with knowledge of web
      archiving and researchers from humanity subjects (History and
      Literature).  This resulted in the paper "Persistent Web

Zierau                  Expires September 2, 2019              [Page 20]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

      References - Best Practices and New Suggestions" [IPRES2016] from
      the iPres 2016 conference.  In this paper, the PWID is referred to
      as WPID.  However, feedback was received displaying a concern that
      WPID was interpreted as a PID related to a PID-system, e.g. as the
      DOI.  Although the definition of a PID does not contradict the
      name "WPID", there would still be a danger of confusing it with
      PID-systems, which is not the intension.  Consequently, this
      suggestion names the PWID instead.

      Comments on the drafted PWID URI ([DraftPwidUri]) have suggested
      that it should be a URN rather than a URI, which is why the PWID
      URN is defined here.

      At the RESAW 2017 conference there were two related papers: One on
      referencing practices [ResawRef] and one on research data
      management practices [ResawColl].  Thesw practices are also
      planned to be used for Danish web collections.

      There has been expressed interest for the PWID URN at several
      occations.  There were lots of response at iPRES 2016.  Especially
      at the RESAW 2017 conference, web researchers from digital
      humanities have expressed a strong interest in the PWID, since it
      will fill a gap and make it possible for the researchers to make
      the necessary references.

      At iPRES 2018, the PWID URN was presented as a digital poster,
      which gained a lot of interest and won the "Best poster" award
      [IPRES2018].

      A more researcher-oriented poster was presented at iDCC 2019
      [IDCC2019].

   Revision Information:

      This is the sixth version of PWID as a URN, where remarks from the
      recent PWID URN reviews have been incorporated.  The changes
      includes the following:

      *  Change of syntax for archive-id, to distinguish between domains
         of web archives and future registered identifiers for web
         archives.  Furthermore, the description of archive identifiers
         as well as assignment and resolution of PWIDs have been updated
         accordingly.

      *  Change of syntax for archived-item (and renamed to archived-
         item-id for consistency purposes) , to distinguish between URIs
         and other identifiers.  Furthermore, the description of

Zierau                  Expires September 2, 2019              [Page 21]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

         archived item identifiers as well as assignment and resolution
         of PWIDs have been updated accordingly.

      *  Change of syntax for precision-spec, where the option "other"
         is removed and replaced with extension values.  The description
         of precision specification has been updated accordingly.

      *  The description of the archived URI description has been
         updated, so %-ending includes encoding of "%" in order to
         achive unambiguous use of "%" in URN PWIDs.

      *  Change of syntax for archival-time to a more rigid
         specification in order to make it more clear what is allowed.
         The description of archival time has been updated accordingly

      *  The reference [W3CDTF] has been updated to appear in a better
         format.

3.  Acknowledgements

   A special thanks to Caroline Nyvang and Thomas Kromann who have
   contributed to the research identifying the minimum information
   required in a persistent web reference, and to Bolette Jurik who
   contributed with supplementary research concerning requirements for
   web collection/corpora definitions.  Also thanks to everybody who has
   contributed to this work with the research parts and with reviewing
   of this RFC.

4.  References

4.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

Zierau                  Expires September 2, 2019              [Page 22]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC8141]  Saint-Andre, P. and J. Klensin, "Uniform Resource Names
              (URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017,
              <https://www.rfc-editor.org/info/rfc8141>.

4.2.  Informative References

   [DOI]      International DOI Foundation, "The DOI System", 2016,
              <https://web.archive.org/web/20161020222635/
              https:/www.doi.org/>.

              urn:pwid:archive.org:2016-10-20T22:26:35:site:https://www.
              doi.org/

   [DraftPwidUri]
              Zierau, E., "DRAFT: Scheme Specification for the pwid URI,
              version 4", June 2018, <https://datatracker.ietf.org/doc/
              draft-pwid-uri-specification/>.

   [IDCC2019]
              Zierau, E., "Web References Meeting Requirements for
              Proper Referencing Principles"", February 2019,
              <http://www.dcc.ac.uk/sites/default/files/documents/IDCC19
              /222_Web%20References%20Meeting%20Requirements%20for%20Pro
              per%20Referencing%20Principles.pdf>.

              Poster at 14th International Digital Curation Conference
              (iDCC) 2019

   [IPRES2016]
              Zierau, E., Nyvang, C., and T. Kromann, "Persistent Web
              References - Best Practices and New Suggestions", October
              2016, <http://www.ipres2016.ch/frontend/organizers/media/
              iPRES2016/_PDF/
              IPR16.Proceedings_4_Web_Broschuere_Link.pdf>.

              In: proceedings of the 13th International Conference on
              Preservation of Digital Objects (iPres) 2016, pp. 237-246

Zierau                  Expires September 2, 2019              [Page 23]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

   [IPRES2018]
              Zierau, E., "Precise and Persistent Web Archive References
              - Status, context and expected progress of the PWID",
              September 2018, <https://osf.io/u5w3q/>.

              In: proceedings of the 15th International Conference on
              Preservation of Digital Objects (iPres) 2018, DOI:
              10.17605/OSF.IO/U5W3Q

   [ISO28500]
              International Organization for Standardization,
              "Information and documentation -- WARC file format", 2017,
              <https://www.iso.org/standard/68004.html>.

   [ISO8601]  International Organization for Standardization, "Data
              elements and interchange formats -- Information
              interchange -- Representation of dates and times", 2004,
              <https://www.iso.org/standard/40874.html>.

   [MEMENTO]  Memento Development Group, "About the Memento Project",
              January 2015, <http://mementoweb.org/about/>.

              urn:pwid:archive.org:2018-11-
              01T15:26:28Z:page:http://mementoweb.org/about/

   [PWIDprovider]
              Royal Danish Library (Netarkivet), "SolrWayback 3.1",
              2018, <https://github.com/netarchivesuite/solrwayback>.

              urn:pwid:archive.org:2018-06-
              11T02:00:05Z:page:https://github.com/netarchivesuite/
              solrwayback

   [PWIDresolver]
              Royal Danish Library (Netarkivet), "Date and Time Formats:
              note submitted to the W3C. 15 September 1997", 2018,
              <https://github.com/netarchivesuite/NAS-research/releases/
              tag/0.0.6>.

              urn:pwid:archive.org:2018-07-
              16T06:53:51Z:page:https://github.com/netarchivesuite/NAS-
              research/releases/tag/0.0.6

   [RESAW]    The Resaw Community, "A Research infrastructure for the
              Study of Archived Web materials", 2017,
              <https://web.archive.org/web/20170529113150/
              http://resaw.eu/>.

Zierau                  Expires September 2, 2019              [Page 24]
Internet-DraAtPersistent Web IDentifier (PWID) URN Namespace  March 2019

              urn:pwid:archive.org:2017-05-29T11:31:50Z:site:http://resa
              w.eu/

   [ResawColl]
              Jurik, B. and E. Zierau, "Data Management of Web archive
              Research Data", 2017,
              <https://archivedweb.blogs.sas.ac.uk/files/2017/06/
              RESAW2017-JurikZierau-
              Data_management_of_web_archive_research_data.pdf>.

              In: proceedings of the RESAW 2017 Conference, DOI:
              10.14296/resaw.0002

   [ResawRef]
              Nyvang, C., Kromann, T., and E. Zierau, "Capturing the Web
              at Large - a Critique of Current Web Referencing
              Practices", 2017,
              <https://archivedweb.blogs.sas.ac.uk/files/2017/06/
              RESAW2017-NyvangKromannZierau-
              Capturing_the_web_at_large.pdf>.

              In: proceedings of the RESAW 2017 Conference, DOI:
              10.14296/resaw.0004

   [W3CDTF]   W3C, "Date and Time Formats: note submitted to the W3C. 15
              September 1997", 1997,
              <http://www.w3.org/TR/NOTE-datetime>.

              urn:pwid:archive.org:2017-04-
              03T03:37:42Z:page:http://www.w3.org/TR/NOTE-datetime

Author's Address

   Eld Maj-Britt Olmuetz Zierau (editor)
   Royal Danish Library
   Soeren Kierkegaards Plads 1
   Copenhagen  1219
   Denmark

   Phone: +45 9132 4690
   Email: elzi@kb.dk

Zierau                  Expires September 2, 2019              [Page 25]