Web archiving is the process of collecting portions of the World Wide Web to ensure the information is preserved in an archive for future researchers, historians, and the public. Web archivists typically employ web crawlers for automated capture due to the massive size and amount of information on the Web. The largest web archiving organization based on a bulk crawling approach is the Internet Archive which strives to maintain an archive of the entire Web. The International Web Archiving Workshop (IWAW), begun in 2001, has provided a platform to share experiences and exchange ideas. The later founding of the International Internet Preservation Consortium (IIPC), in 2003, has greatly facilitated international collaboration in developing standards and open source tools for the creation of web archives. These developments, and the growing portion of human culture created and recorded on the web, combine to make it inevitable that more and more libraries and archives will have to face the challenges of web archiving. National libraries, national archives and various consortia of organizations are also involved in archiving culturally important Web content. Commercial web archiving software and services are also available to organizations who need to archive their own web content for corporate heritage, regulatory, or legal purposes.
Provenance and development
Early practice of web archiving involved the highlighting of a “site of the week award” as a record for the contest. Besides that, another early practice was the professional link list (for example Amnesty International’s list of human rights groups) and (Yahoo!) directory and Open Directory Project.
In the mid-1990s, one of the more important listing sites of its kind continually updated an index of worthwhile website destinations organized by content category.
In 1998, Yahoo directory was considered to have made a significant contribution to newfangled online library science, not only by its classification scheme but also by the means of the content “navigation” it developed.
Soliciting, evaluating, and categorizing websites - the large-scale collecting, hand-sorting, and display of websites - could be considered an original form of website analysis. The rise of the algorithmic search engine has largely led to the disappearance of such manual methods.
Collecting the web
Methods of collection
The most common web archiving technique uses web crawlers to automate the process of collecting web pages. Web crawlers typically access web pages in the same manner that users with a browser see the Web, and therefore provide a comparatively simple method of remote harvesting web content. Examples of web crawlers used for web archiving include:
Database archiving refers to methods for archiving the underlying content of database-driven websites. It typically requires the extraction of the database content into a standard schema, often using XML. Once stored in that standard format, the archived content of multiple databases can then be made available using a single access system. This approach is exemplified by the DeepArc and Xinq tools developed by the Bibliothèque nationale de France and the National Library of Australia respectively. DeepArc enables the structure of a relational database to be mapped to an XML schema, and the content exported into an XML document. Xinq then allows that content to be delivered online. Although the original layout and behavior of the website cannot be preserved exactly, Xinq does allow the basic querying and retrieval functionality to be replicated.
Transactional archiving is an event-driven approach, which collects the actual transactions which take place between a web server and a web browser. It is primarily used as a means of preserving evidence of the content which was actually viewed on a particular website, on a given date. This may be particularly important for organizations which need to comply with legal or regulatory requirements for disclosing and retaining information.
A transactional archiving system typically operates by intercepting every HTTP request to, and response from, the web server, filtering each response to eliminate duplicate content, and permanently storing the responses as bitstreams.
Difficulties and limitations
Web archives which rely on web crawling as their primary means of collecting the Web are influenced by the difficulties of web crawling:
- The robots exclusion protocol may request crawlers not access portions of a website. Some web archivists may ignore the request and crawl those portions anyway.
- Large portions of a web site may be hidden in the Deep Web. For example, the results page behind a web form can lie in the Deep Web if crawlers cannot follow a link to the results page.
- Crawler traps (e.g., calendars) may cause a crawler to download an infinite number of pages, so crawlers are usually configured to limit the number of dynamic pages they crawl.
However, it is important to note that a native format web archive, i.e., a fully browsable web archive, with working links, media, etc., is only really possible using crawler technology.
The Web is so large that crawling a significant portion of it takes a large amount of technical resources. The Web is changing so fast that portions of a website may change before a crawler has even finished crawling it.
Some web servers are configured to return different pages to web archiver requests than they would in response to regular browser requests. This is typically done to fool search engines into directing more user traffic to a website, and is often done to avoid accountability, or to provide enhanced content only to those browsers that can display it.
Not only must web archivists deal with the technical challenges of web archiving, they must also contend with intellectual property laws. Peter Lyman states that "although the Web is popularly regarded as a public domain resource, it is copyrighted; thus, archivists have no legal right to copy the Web". However national libraries in some countries  have a legal right to copy portions of the web under an extension of a legal deposit.
Some private non-profit web archives that are made publicly accessible like WebCite, the Internet Archive or the Internet Memory Foundation allow content owners to hide or remove archived content that they do not want the public to have access to. Other web archives are only accessible from certain locations or have regulated usage. WebCite cites a recent lawsuit against Google's caching, which Google won.
Aspects of web curation
Web curation, like any digital curation, entails:
- Certification of the trustworthiness and integrity of the collection content
- Collecting verifiable Web assets
- Providing Web asset search and retrieval
- Semantic and ontological continuity and comparability of the collection content
Thus, besides the discussion on methods of collecting the Web, those of providing access, certification, and organizing must be included. There are a set of popular tools that addresses these curation steps:
A suite of tools for Web Curation by International Internet Preservation Consortium:
- Heritrix - collecting Web asset
- NutchWAX - search Web archive collections
- Open source Wayback Machine - search and navigate Web archive collections using NutchWax
- Web Curator Tool - Selection and Management of Web Collection
Other open source tools for manipulating web archives:
- WARC Tools - for creating, reading, parsing and manipulating, WARC archives programmatically
- Google Search Tools - for indexing and searching full-text and metadata within web archives
Free but not open source tools also exists:
- WARC Software Development Kit (WSDK) represents a set of simple, compact, and highly optimized Erlang modules to manipulate (create/read/write) the WARC ISO 28500:2009 file format.
- Archive site
- Archive Team
- Common Crawl
- Digital preservation
- List of Web archiving initiatives
- Memento Project
- Minerva Initiative
- National Digital Information Infrastructure and Preservation Program (NDIIPP)
- National Digital Library Program (NDLP)
- Pandora Archive
- Portuguese Web Archive
- UK Web Archiving Consortium
- Virtual artifact
- Wayback Machine
- Web crawling
- Habibzadeh, P.; Sciences, Schattauer GmbH - Publishers for Medicine and Natural (2013-01-01). "Decay of References to Web sites in Articles Published in General Medical Journals: Mainstream vs Small Journals". Applied Clinical Informatics. 4 (4). doi:10.4338/aci-2013-07-ra-0055.
- Habibzadeh, Parham (2015-07-30). "Are current archiving systems reliable enough?". International Urogynecology Journal: 1–1. doi:10.1007/s00192-015-2805-7. ISSN 0937-3462.
- Lyman (2002)
- "Legal Deposit | IIPC". netpreserve.org. Retrieved 2017-01-31.
- FAQ Webcitation.org
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- Brügger, N. (2005). Archiving Websites. General Considerations and Strategies. Aarhus: The Centre for Internet Research. ISBN 87-990507-0-6. Archived from the original on 2009-01-29.
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- Jacoby, Robert (August 19, 2010). "Archiving a Web Page". Archived from the original on 2011-01-03. Retrieved 23 October 2010.
- Lyman, P. (2002). "Archiving the World Wide Web". Building a National Strategy for Preservation: Issues in Digital Media Archiving.
- Masanès, J. (ed.) (2006). Web Archiving. Berlin: Springer-Verlag. ISBN 3-540-23338-5.
- Pennock, Maureen (2013). Web-Archiving. DPC Technology Watch Reports. Great Britain: Digital Preservation Coalition. doi:10.7207/twr13-01. ISSN 2048-7916.
- Toyoda, M., Kitsuregawa, M. (2012). "The History of Web Archiving". Proceedings of the IEEE. 100 (special centennial issue). doi:10.1109/JPROC.2012.2189920.
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- International Internet Preservation Consortium (IIPC) - International consortium whose mission is to acquire, preserve, and make accessible knowledge and information from the Internet for future generations
- International Web Archiving Workshop (IWAW) - Annual workshop that focuses on web archiving
- National Library of Australia, Preserving Access to Digital Information (PADI)
- Library of Congress - Web Archiving
- Web archiving bibliography - Lengthy list of web-archiving resources
- Julien Masanès, Bibliothèque Nationale de France - Towards continuous web archiving
- Comparison of web archiving services
- List of blogs about web archiving, 2015