Persistent Web IDentifier (PWID)         

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Royal Danish Library uses PWID as the recommended way to reference web archive material

The Persistent Web IDentifier (PWID) is used for creation and resolving of precise and persistent references to data in web archives. PWID was created as there was no proper way of referring precisely and persistently to data in one or more web archives.

A PWID can be specified in two ways

  • as a Uniform Resource Name (URN)
  • as a textual reference, e.g. by using the ISO-690 standard


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PWID is constructed in a way that makes it both human readable and algorithmically resolvable by tools in form of a URN. PWID is useful in research data management based on material from web archives, but also as reference to web material in research reports and papers. The creation of PWID is a result of a research project in 2016, with participants across research fields, which made it possible to bridge the gap between humanities and computer science research.

Further work will be to establish some kind of registry for web archives for identification (e.g. via domains) of web archives as part of PWID (e.g. via International Internet Preservation Consortium/IIPC). Another initiative is creation of a PWID-URN resolver, which currently exists only as a prototype (and might end up as e.g. a Open Preservation Foundation/OPF tool).

PWID is presented in various litterature, posters and presentations. You will find most of it in the following lists of updated PWID descriptions, examples of use, and historical background.

Formal PWID URN description

Other PWID descriptions

Examples of use

Historical background

Web archive registry work