A Persistent Web IDentifier (PWID) URN Namespace
draft-pwid-urn-specification-03
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 exact referencing method which includes support for references to archives with restricted access, for exact references to existing web material, and for exact specification of elements in a web corpus (possibly spanning over several web archives). The PWID URN therefore offers a scheme to make references that are not currently supported.
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, and in a way that can make them potentially resolvable.
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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 e.g. to make them resolvable
- can cover references to all sorts of materials in web archives
- can 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 [IPRES] 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.
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 [RFC2119].
2. Namespace Registration Template
Namespace Identifier:
Version:
Date:
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 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 e.g. to make them resolvable
- can cover references to all sorts of materials in web archives
- can 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. This regards 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 [IPRES] 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 unambiguous syntax is needed for the PWID reference 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, which strict syntax can make possible. Examples of technical solutions that is enabled by strict 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 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.
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) [RFC5234] and it conforms to URN syntax defined in RFC 8141. The syntax definition of the PWID URN is:
- '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 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
Assignment:
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:
- 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 to the URI standard defined as in RFC 3986W3C profile ISO 8601 (also defined in RFC 3339) and to the WARC standard ISO 28500 using UTC dates only
- the 'archived-item' is a URI which 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. esolution 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.
- 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 broudly available or can be installed locally. This service currently covers bothe the Danish web archives (with the proper rights) and open web archives with access sevices based on a patterns including archive, archival time and archived URI. In other words, for open web archives it covers conversion of PWIDs for: archive.org, archive-it.org, arquivo.pt, bibalex.org, nationalarchives.gov.uk, stanford.edu and vefsafn.is. The source code for this prototyppe is available from https://github.com/netarchivesuite/NAS-research/releases/tag/0.0.6.
Resolution (manually or automatically) is done based on the PWID parts:
- 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 part as the reference in the way that the content coverage specifies, i.e. for a webpage the value 'part' would mean the html of the web page, 'webpage' would mean the resoult of the web archive rendering the referred html as a web page etc.
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 (which the current prototype does for references to the Danish Netarkivet). 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.
Automatic access of a referenced web resource may work on the open net 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:
- 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:
Additional Information:
- The PWID was originally 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.
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. The textual version of the PWID is also suggested in a textual form in a draft of the revision of the ISO 690 reference standard.
Revision Information:
- This is the third version of PWID as a URN, where prototypes for resolving a PWID and getting PWIDs for a web page has been added and explained. Furthermore, it has been made more clear where the PWID URN makes a difference and "closed archives" have to "archives with restricted access"
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
| [RFC2119] |
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC3339] |
Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002. |
| [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. |
| [RFC5234] |
Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008. |
| [RFC8141] |
Saint-Andre, P. and J. Klensin, "Uniform Resource Names (URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017. |
4.2. Informative References
| [DOI] |
International DOI Foundation, "The DOI System", 2016. 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. |
| [IPRES] |
Zierau, E., Nyvang, C. and T. Kromann, "Persistent Web References - Best Practices and New Suggestions", October 2016. In: proceedings of the 13th International Conference on Preservation of Digital Objects (iPres) 2016, pp. 237-246
|
| [ISO28500] |
International Organization for Standardization, "Information and documentation -- WARC file format", 2017. |
| [ISO8601] |
International Organization for Standardization, "Data elements and interchange formats -- Information interchange -- Representation of dates and times", 2004. |
| [PWIDprovider] |
Royal Danish Library (Netarkivet), "SolrWayback 3.1", 2018. 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. 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. pwid:archive.org:2017-05-29T11:31:50Z:site:http://resaw.eu/
|
| [ResawColl] |
Jurik, B. and E. Zierau, "Data Management of Web archive Research Data", 2017. 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. In: proceedings of the RESAW 2017 Conference, DOI: 10.14296/resaw.0004
|
| [RFC6068] |
Duerst, M., Masinter, L. and J. Zawinski, "The 'mailto' URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010. |
| [W3CDTF] |
W3C, "Date and Time Formats: note submitted to the W3C. 15 September 1997", 1997. W3C profile of ISO 8601 urn:pwid:archive.org:2017-04-03T03:37:42Z:page:http://www.w3.org/TR/NOTE-datetime
|
Eld Maj-Britt Olmuetz Zierau (editor)
Zierau
Royal Danish Library
Soeren Kierkegaards Plads 1
Copenhagen,
1219
Denmark
Phone: +45 9132 4690
EMail: elzi@kb.dk