A Persistent Web IDentifier (PWID) URN Namespace
draft-pwid-urn-specification-01

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 purpose of the standard is to support general, global, sustainable, humanly readable, technology agnostic, persistent and precise web references for web materials.

The PWID URN can assist in two ways: First, by providing potential resolvable precise and persistent reference scheme for documents, which is not sufficiently covered by existing web reference practices. Second, by providing a standardized way to specify web elements in 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.

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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 purpose of the PWID URN is to represent general, global, sustainable, humanly readable, technology agnostic, persistent and precise web archive resource references - in a way that can be used for technical solutions.

The motivation for defining a PWID namespace is the growing challenge of references to web resources, - both regarding referencing web resources from papers and regarding definition of web collection/corpus - calls for action now, which can be provided with PWID as a URN, allthough the prefixing with "urn:" is not ideal. In deatail 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 [IPRES] and [ResawRef]).
• 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 and [ResawColl]).

For the sake of usability and sustainability, the definition of 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 coverage (page, part, subsite etc.)

The PWID URN represents this information in an unambiguous way, and thus enabling technical solutions to be defined in this 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 RFC 2119.

2. Namespace Registration Template

Namespace Identifier:

• PWID

Version:

• 1

Date:

• 2017-12-08

Registrant:

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

Purpose:

• The purpose of the PWID URN is to represent general, global, sustainable, humanly readable, technology agnostic, persistent and precise web archive resource references - in a way that can be used for technical solutions. The standard is needed to address web materials meeting precision and persistency issues on par precision in with traditional references for analogue material.
  
  The scope and applicability of the PWID URN is both references to archived web resources from literature as well as basis for defining parts of a archived web collection. Strict unambiguous syntax is needed in order to ensure that it can be used for computational purposes. This is relevant for web collection definitions, which will need a strict syntax in order to be a basis for automatic extraction. 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.
  
  The interest for this new PWID has already been shown, a paper about the invention of the PWID "Persistent Web References - Best Practices and New Suggestions" [IPRES] was accepted for the iPres 2016 conference and nominated as best paper. At the RESAW 2017 conference there are two related papers: One on referencing practices [ResawRef] and one on research data management practices [ResawColl]. The interest for the PWID so far indicates that this is a recognized issue, and that the PWID can fill a gap.
  
  The PWID URN is to represent this information in a way that can be used for technical solutions, for example for resolving of a references and automatic extraction of web collection defined by PWID URNs [ResawRef] [ResawColl]. There may come different implementations for resolving which may rely on different protocols and application. As a start there is work on a prototype that can work for the Danish Netarkiv data and open web archives with standard patterns for the current technologies. Further work will be done to make this more internationally integrated.
  
  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. The textual version of the PWID (see additional information) is already in draft of the revision of the ISO 690 reference standard.

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

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

                 archive-id  = +( unreserved )
               

                 archival-time   = full-date datetime-delim full-pwid-time
                 datetime-delim  = "T"
                 full-pwid-time  = time-hour [":"] time-minute [":"] time-second "Z"
               

                 coverage-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) RFC 5234 and it conforms to URN syntax defined in RFC 8141. The syntax definition of the PWID URN is:
• where
  • 'unreserved' is defined as in RFC 3986
  • 'coverage-spec' values are not case sensitive (i.e. "PAGE" / "PART" / "PaGe" / ... are valid values as well.)
  • 'archival-time' is a UTC timestamp conforming to the W3C profile ISO8601 ISO 8601 (also defined in RFC 3339), with a few exception. It has to be a UTC timestamp in order to conform with web archiving practices, which always uses UTC in order to avoid confusions. The 'full-date' is defined as in RFC 3339. The 'archival-time' must represent the time specified in the archive, and can therefore be specified at any of the levels of granularity as described in [W3CDTF] and in accordance with teh WARC standard ISO 28500.
    
    In line with RFC 3339 the "T" may alternatively be lower case "t".
    
    'time-hour', 'time-minute' and 'time-second' are defined as in RFC 3339.
    
    In line with RFC 3339 the "Z" may alternatively be lower case "z".
  • 'URI' is defined as in RFC 3986

• The 'coverage-spec' defines the type of archived item, serving as a precision to what is referred:
  • part
    the single archived element, e.g. a pdf, a html text, an image
  • page
    the full context as a page, e.g. a html page with referred images
  • subsite
    the full context as a subsite within its domain, e.g. a document represented in a web structure
  • site
    the full context as a site within its domain
  • collection
    a collection/corpora definition, e.g. defined as descibed in [ResawColl]
  • snapshot
    a snapshot (image) representation of web material, e.g. a web page
  • recording
    a recording of a web browsing
  • other
    if something else

• Note that the 'coverage-spec' is a parameter that could have been specified as a query. However, since the 'pwid-urn' can include an URI as 'archived-item', it would introduce ambiguities if the 'coverage-spec' was specified as a query, since it would not be clear whether the query belonged to the 'pwid-urn' or the 'archived-item'.

Assignment:

• There are no authorities for assigning PWID URNs to resources, as the rule is the it is the given by the syntax that the name is assigned according to the
  • Identification of web archive
  • Identification of source:
    • Archived URI or identifier
    • Archival timestamp

  • Intended coverage (page, part, subsite etc.)

  Therefore, the PWID URNs are created independently, but following an algorithm that itself guarantees uniqueness.

  
  
  The name will always be unique, as the only way to define a clash would be that a web archive cease to exist, and by time another web archive gets the same name space and have resources with the same name and same archiving timestamp, but with different contents. This is a highly unlikely scenario.

Security and Privacy:

• Security and privacy considerations are restricted to accessible web resources in web archives. If resolvers to PWID URNs are created, there should be made an analysis of whether they can be restricted to the former mentioned registry of web archives. Security and privacy will then be a question of security and privacy considerations related to the web archive resources.

Interoperability:

• This is covered by comments in the Syntax description, where the 'archival-time' conforms to the W3C profile ISO 8601 (also defined in RFC 3339) and use of date conforms to the WARC standard ISO 28500 using UTC dates only. Furthermore, the when the 'archived-item' is a URI, this conforms to the URI standard defined as in RFC 3986.

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. The plan is to develop a resolving service, but this is only in a prototype form at the moment.
  
  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:
  • Web archive identification
    to find the archive holding the material
  • Archived URI or identifier of item
    as part of identifying the material
  • Date and time associated with the archived URI/item
    as part of precise identification of the material
  • Coverage of what is referred
    as part of clarification of what the referred material covers (page, part etc.)

  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 domian name for their open access web archive
  • 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

  With knowledge of the current (2017) Internet Archive open access web interface having the form:

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

  We can manually (or technically) deduce an actual (current 2017) access https address:

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

  and regard the referred web page as the reference.

  
  
  The same recipe can be used for other Wayback platforms - and possibly also other web archive access tools platforms, as the crucial information is date and URI, which are requested to be looked up in a specified archive.
  
  Note that this also includes access to archives that are only accessible via a local proxy to a restricted environment. Here the difference is that the archive information is used to identify the local environment used (possibly on-site) and then construct local http/https address based on knowledge from the local access installation. In November there was created a prototype for PWIDs to the Netarkivet, and there are plans to extend it.
  
  Automatic access of a referenced web resource may work on the open net for open web archive or in restricted environments for the closed web archives. 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:
    • http/https URIs for standard web archive interfaces
      At this stage there are initiatives on streamlined and standardize APIs to web archives interfaces, - and in case such APIs will be implemented generally, it may be used for resolving of the PWID URNs. This could be on form (denoting pwid parts in <> using syntax names):
      • https://<archive-id>/pwid?time=<archival-time>&coverage=<coverage-spec>&item=<archived-item>

      The example from previous section would then resolve by

      • https://archive.org/pwid?time=2016-01-22T11:20:29Z&coverage=page&item=http://www.dr.dk

    • http/https URIs for archive material for individual web archives
      Using the current open access http/https address pattern for the individual web archives, which for the example is
      • https://web.archive.org/web/20160122112029/http://www.dr.dk

      This would require a registry of the different patterns for the individual web archives

  • 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]. The PWID URN resolving could in such cases be a question of starting a special application, as for the 'mailto' scheme RFC 6068.

Documentation:

• None relevant

Additional Information:

• The PWID was orininally suggested as a URI based on research between a computer science researcher with know of web archiving and researchers from humanity subject (History and Literature). This resulted in the paper "Persistent Web References - Best Practices and New Suggestions" [IPRES] 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, although there is a danger that users of the reference style can be confused by the the additional "urn:" prefix.
  
  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.

Revision Information:

• This is the initial version of PWID as a URN

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/copora 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