A Persistent Web IDentifier (PWID) URN Namespace
draft-pwid-urn-specification-04

Abstract

This document specifies a Uniform Resource Name (URN) for Persistent Web IDentifiers to 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 it can be used in specifying web collections, which then can form a persistent computational basis for the extract of the archived collection parts. Since the parts can be specified generally, this further allow collections to be specified with elements from one or more web archives.

The PWID is designed for researchers and therefore it is designed as general, global, sustainable, humanly readable, technology agnostic, persistent and precise web references for web materials in web archives.

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Namespace Registration Template
• 3. Acknowledgements
• 4. References
• 4.1. Normative References
• 4.2. Informative References
• Author's Address

1. Introduction

The URN PWID is a supplement to existing reference standards, where the PWID 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, it enables technology agnostic references to web archives in general, which can for instance can be needed for references to web material that is dynamic (e.g. a news site) or a specific version of a web material (e.g. specific version of the DOI handbook).

The URN PWID is a form that can work as an algorithmic basis for finding the resource. This also enables basis for computation of archived web parts to a collection from one or more web archives.

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

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

• be used for technical solutions e.g. to make them resolvable
• cover references to all sorts of materials in web archives
• cover references to materials from all sort of web archives

The motivation for defining a PWID namespace is the growing challenge of references to archived web resources, which the PWID as a URN can assist in overcoming. The standard is needed to address web materials meeting precision and persistency issues on par precision in with 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 collection/corpus. In detail the challenges are:

• Citation guidelines generally do not cover general and persistent referencing techniques for web resources that are not registered by Persistent Identifier systems (like DOI). However, an increasing number of references point to resources that only exist on the web, e.g. blogs that turned out to have a historical impact. In order to obtain persistency for a reference, the target need to be stable. As the live web is 'alive' and in constant change, persistency can only be obtained by referring to archived snapshots of the web. The PWID URN is therefore focused on referencing archived web material in a technology agnostic way (research documented in [IPRES2016] and [ResawRef]).
• There are many new initiatives for web archive referencing, - most of them are centralised solutions which offers harvest and referencing, but these cannot be used for existing materials in web archives. Other initiatives only cover open web archives, which does not cover material in archives with restricted access and where there is a risk of imprecision if a resource in an alternative archive is the result of resolving such a resource. The PWID URN is needed in order to fill these gaps where other techniques are not sufficient.
• There are many different requirements for construction of collection definitions for web material besides precision and persistency. Recent research have found that various legal and sustainability issues leads to a need for a collection to be defined by references to the web parts in the collection. The PWID URN is needed in such definitions in order to fulfil these requirements and to enable a collection to cover web materials from more archives (research documented in [ResawColl]).

The PWID is especially useful for web material where precision is in focus and/or there are references to materials from web archives requiring special grants 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 about what is actually referred by the reference (e.g. is it the page or the whole website).

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

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

• resolving of a references and automatic extraction of web collection defined by PWID URNs [ResawRef] [ResawColl]
• Resolving of a PWID reference by resolving services. As a start, there is work on a prototype that can work for the Danish web archive data and open web archives with standard patterns for the current technologies. There may come different implementations for resolving which may rely on different protocols and application

The purpose of the PWID is also to express a web archive reference as simple as possible and at the same time meeting requirements for sustainability, usability and scope. Therefore, the PWID URN is focused on only having the minimum required information to make a precise identification of a resource in an arbitrary web archive. Resent research have found that this is obtain by the following information

• 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.

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].

2. Namespace Registration Template

Namespace Identifier:

• PWID

Version:

• 4

Date:

• 2018-11-03

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 URN PWID is a supplement to existing reference standards, where the PWID 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 it enables technology agnostic references to web archives in general, which can for instance can be needed for references to web material that is dynamic (e.g. a news site) or a specific version of a web material (e.g. specific version of the DOI handbook).
• The URN PWID is a form that can work as an algorithmic basis for finding the resource. This also enables basis for computation of archived web parts to a collection from one or more web archives.
• Furthermore, the PWID includes information about the resource which makes it possible to find alternative resources, in cases where the original precise resource have become unavailable.
• The PWID URN is designed to be a persistent reference that is general, global and technology agnostic in order to enhance its chances for being sustainable. Furthermore, it is designed to be humanly readable and with ability to make precision of the web archive resource covers. This design enables a PWID URN to:
  • be used for technical solutions e.g. to make them resolvable
  • cover references to all sorts of materials in web archives
  • cover references to materials from all sort of web archives

  The motivation for defining a PWID namespace is the growing challenge of references to archived web resources, which the PWID as a URN can assist in overcoming. The standard is needed to address web materials meeting precision and persistency issues on par precision in with 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 collection/corpus. In detail the challenges are:

  • Citation guidelines generally do not cover general and persistent referencing techniques for web resources that are not registered by Persistent Identifier systems (like DOI). However, an increasing number of references point to resources that only exist on the web, e.g. blogs that turned out to have a historical impact. In order to obtain persistency for a reference, the target need to be stable. As the live web is 'alive' and in constant change, persistency can only be obtained by referring to archived snapshots of the web. The PWID URN is therefore focused on referencing archived web material in a technology agnostic way (research documented in [IPRES2016] and [ResawRef]).
  • There are many new initiatives for web archive referencing, - most of them are centralised solutions which offers harvest and referencing, but these cannot be used for existing materials in web archives. Other initiatives only cover open web archives, which does not cover material in archives with restricted access and where there is a risk of imprecision if a resource in an alternative archive is the result of resolving such a resource. The PWID URN is needed in order to fill these gaps where other techniques are not sufficient.
  • There are many different requirements for construction of collection definitions for web material besides precision and persistency. Recent research have found that various legal and sustainability issues leads to a need for a collection to be defined by references to the web parts in the collection. The PWID URN is needed in such definitions in order to fulfil these requirements and to enable a collection to cover web materials from more archives (research documented in [ResawColl]).

  The PWID is especially useful for web material where precision is in focus and/or there are references to materials from web archives requiring special grants in order to gain access. The precision regards both regards precise reference where there can be no doubt about that you have the correct web material as well as precision about what is actually referred by the reference (e.g. is it the page or the whole website)

  
  
  Furthermore, the PWID is very useful in specification of contents of a web collection (also known as web corpus). Definitions of web collections are often needed for extraction of data used in production of research results, e.g. for evaluations in the future. Current practices today are not persistent as they often use some CDX version, which vary for different implementations.
  
  Strict syntax is needed for the PWID reference in order to ensure that it can be used for computational purposes. This is especially relevant for automatic extraction of parts from web collection definitions. Furthermore, readers of research papers are today expecting to be able to access a referenced resource by clicking an actionable URI, therefore a similar facility will be expected for references to available archived web material, which strict syntax can make possible. Examples of technical solutions that is enabled are:
  • resolving of a references and automatic extraction of web collection defined by PWID URNs [ResawRef] [ResawColl]
  • Resolving of a PWID reference by resolving services. As a start, there is work on a prototype that can work for the Danish web archive data and open web archives with standard patterns for the current technologies. There may come different implementations for resolving which may rely on different protocols and application

  The purpose of the PWID is also to express a web archive reference as simple as possible and at the same time meeting requirements for sustainability, usability and scope. Therefore, the PWID URN is focused on only having the minimum required information to make a precise identification of a resource in an arbitrary web archive. Resent research have found that this is obtain 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.

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

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

        archive-id = +( unreserved )
               

        precision-spec = "part" / "page" / "subsite" / "site" 
                 / "collection" / "recording" / "snapshot"
                 / "other"
               

        archived-item = URI / archived-item-id
        archived-item-id = +( unreserved )
               

Syntax:

• The syntax of the PWID URN is specified below in Augmented Backus-Naur Form (ABNF) [RFC5234] and it conforms to URN syntax defined in [RFC8141]. The syntax definition of the PWID URN is:
  • 'archival-time' is a UTC timestamp as described in the W3C profile of [ISO8601] [W3CDTF] (also defined in [RFC3339]), for example YYYY-MM-DDThh:mm:ssZ. The 'archival-time' shall represent the timestamp that the web archive have recorded for the referenced archived URI. The archival-time may be specified at any of the levels of granularity described in [W3CDTF], as long as it reflects exactly the granularity of the timestamp recorded in the web archive, which is in accordance with the WARC standard [ISO28500].
  • 'unreserved' is defined as in [RFC3986]
  • 'precision-spec' values are not case sensitive (i.e. "PAGE" / "PART" / "PaGe" / ... are valid values as well.)
  • 'URI' is defined as in [RFC3986] but where occurrences of "[", "]", "?" and "#" are %-encoded in order not to clash with URN reserved characters [RFC8141]

• The precision specification is expressing the intended precision of the reference. For example, if the reference is to an html web element, this element can be interpreted in several ways:
  • As just one web part
    Meaning the file containing the html, and precisely this file
  • A web page
    Meaning that an application like Wayback shows result in a browser, and calculates referenced web parts (display templates, images etc.) and use these found web parts in the result.
    If the full reference only contains the PWID URN for the page, this may mean that the archived page can change look over time, e.g. in case that parts referred by the page did not exist at reference time, but are harvested at a later stage, - or in case the web archive's algorithm for calculation of the referred web parts are changed and given a different result.
    In order to make a precise reference to a picture in context of a web page, the most precise reference will be to provide the PWID URN for the page (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 result in a browser showing the web page, - and if there are restricted access according to the reference, the application also needs 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 an URN PWID in order to enable the person making the above described precision in the reference. Furthermore this precesion specification will make it possible for resolvers to display the referred source in a way that corresponds to the precision specification.

• Especially for web materials, there can be 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, there are also web archives that archive snapshots of the web pages for the archived URI. A third option can be 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.
• As consequence of the above, there are following valid precision-spec values:
  • part
    the single archived web part harvested as a file from the specified URI, e.g. a pdf, an html text, an image
  • page
    the web page represented by the web page file (e.g. html) harvested from the specified URI, where this contents 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
    The referred web page (as described under 'page') where it 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') where it is possible to browse to all references in the domain specified in the archived URI
  • collection
    Representation of a collection specification, where it is up to the web archive applications to find out 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 it is up to the web archive applications to find out how it is rendered (where interpretation could depends on file-suffix for the web recording), an example is web recording coded in a WARC file
  • other
    This is a placeholder to allow reference of a resource of any kind with an assigned identifier (by the archive). In all cases, it will be up to the application serving the web archive to interpret how this item should be rendered

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

Assignment:

• The PWID URNs does not have to be assigned by an authority, as they are based on the information created at the time of archiving. In other words: the PWID URNs are created independently, but following an algorithm which ensures that the referred item can be found if it is still available. It also has the benefit that it includes information to look alternative resources e.g. via Memento for some open web archives [MEMENTO] or via possibly coming web archive infrastructures.
• A PWID URN is created by finding the relevant information of the syntax parts of the PWID on form:
  • 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 Archives open web archive). This is recommended, since browsing of this domain page typically will lead to description of how to access the web archive, e.g. online 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 in the same organisation, e.g. archive.org and archive-it.org are both covered by Internet Archive. When a registry of web archives are 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 domain netarkivet.dk)
  • archival-time (archival timestamp):
    The archival time for the archived item in hand may be displayed along with the archived item, but there are different implementation where it is important to be aware of whether a more precise timestamp can be found, and that it is the correct timestamp that is used. For many Wayback implementation the precise time can be found as part of the URI used for viewing the archived item, e.g. in the example of https://web.archive.org/web/20160122112029/http://www.dr.dk viewable by the Internet Archives Wayback installation, the number 20160122112029 represents the archival time 2016-01-22T11:20:29Z. In other installations. In other installations, the most precise time 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 based on calculations or browse on basis of collection of specific parts).
    Since the archived URI can have different forms indicated by the precision specification, this information may be used in resolution and location.
    For most imprecision types are the ones that involves calculation, i.e. page, site or subsite. For items like an image that have no references to calculate the precision is best described by part, since it also tells that it is a precise reference.
  • archived-item (archived URI or identifier):
    The archived item will be the URI (or identifier assigned for a resource by the archive) of the displayed the archived item in hand.

  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 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
  • 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:

• 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 RFC 3986 and the URN standard RFC 8141
  • the 'archival-time' of the PWID URN conforms UTC timestamp as described in the W3C profile of ISO 8601 [W3CDTF] and is in accordance with the WARC standard ISO 28500.
  • the 'archived-item' is either an assigned identifier (the URN standard RFC 8141) or an URI which conforms to the URI standard defined as in RFC 3986, with %-encodings of "[", "]", "#", and "?" in order to conform to the the URN standard RFC 8141

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
    The identifier is either an identifier where location of the web archive can be found by looking up the identifier in a registry, - or it 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, e.g. online or by applying for access grants
  • Archived URI or identifier of archived item
    If the resource is an archived URI, this URI must be used in search for or construction of location of the resource. If the resource is an identifier assigned to the resource (by the archive), it is 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 "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

  Based on the current (2018) knowledge of Internet Archive's open access web interface, which has the pattern:

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

  If the web archive has registered an identifier for the web archive along with the prefix before <time> and <uri>, then this identifier can be used to manually (or automatically) deduce the prefix via this register

• we can manually (or automatically) deduce an actual (current 2018) access https address for Internet Archives Wayback application (where only digits from the date is included):
  • 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 would be 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.
• It is also noteworthy that the information in the PWID can help in finding an alternative resource, in case the original referred resource is not available anymore. The archived URI can be searched in other web archives, where the date and time can help to find the best match found, e.g. via Memento (for some open web archives) or via possibly coming web archive infrastructures.
• Regarding the precision specification, there are not yet any 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 broadly available. This service currently covers both the Danish web archive (with the proper rights) and open web archives with access services based on a patterns 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 archive 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 do not yet exists. 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, where the suggestion was based on research between a computer science researcher with knowledge of web archiving and researchers from humanity subject (History and Literature). This resulted in the paper "Persistent Web References - Best Practices and New Suggestions" [IPRES2016] from the iPres 2016 conference. In this paper, the PWID is referred to as WPID. However, one of the feedbacks has been a concern that WPID was interpreted as a PID related to a PID-system, e.g. as the DOI. All though PID does not have a precise definition that makes it wrong to call it a "WPID. The danger is that it is confused with PID systems, which is not the intension. Consequently, this suggestion names the PWID instead.
  
  The comments on the drafted PWID URI ([DraftPwidUri]) has been that is seems to be a URN rather than a URI. Which is the reason why it is now suggested as a URN.
  
  At the RESAW 2017 conference there are two related papers: One on referencing practices [ResawRef] and one on research data management practices [ResawColl]. This practice is also planned to be used for Danish web collections.
  
  The interest for this new PWID has already been shown. There was a lot of response at iPRES. Especially at the RESAW 2017 conference, web researchers from digital humanities have expressed strong interest in the PWID, since it can fill a gap and make it possible for them to make all the references they need to make. Therefore, the ambition is to make the PWID URN namespace definition a constituent part of a standard being developed in the IETF or some other recognized standards body.
  
  At iPRES 2018, the PWID URN was presented in a digital poster, which had a lot of interest around it, and it won the "best poster" award [IPRES2018]. A more researcher-oriented version of this poster has been accepted to iDCC 2019.

Revision Information:

• This is the fourth version of PWID as a URN, where remarks from the URN PWID reviews have been incorporated. This large covers the following:
  • It has been more clear clear that the PWID URN is a needed supplement to existing standards (especially in Abstract and Introduction of RFC, as well as Purpose of URN template)
  • It has been made more clear that the PWID URN also can be used as basis for search of resources that has become unavailable (especially in the Introduction of RFC, as well as Purpose and Resolution sections of URN template)
  • The Introduction section of the RFC and the Purpose section of the URN template has been aligned.
  • 'Coverage' has been renamed to 'precision' and it has been explain in much more details (especially in the Syntax, Assignment and Resolution sections)
  • Use of the term "ambiguity" have been rephrased in order to be more correct
  • 'archival-time' and 'URI' have been decribed in more details and more correctly (in the Syntax section)
  • Description of Assignment has been expanded to provived more thorough and precise description (in the Assignment section)
  • Description of Resolution has been expanded to provived more thorough and precise description (in the Resolution section)
  • The Interoperability descriptions have been adjusted to reflect the descrions in the Syntax section (in the Interoperability section)

  Furthermore the Security and Privacy section has been edited in order to become more clear, and the Additional Information section has been extended with mentioning of the price winning iPRES 2018 poster and coming iDCC 2019 poster.

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 contributed with supplementary research concerning requirements for web collection/corpora definitions. Also thanks to all that have contributed to this work with the research and reviewing this RFC.

4. References

4.1. Normative References

4.2. Informative References

Author's Address