Web archiving

Web archiving is the process of collecting portions of the World Wide Web and ensuring the collection is preserved in an archive, such as an archive site, for future researchers, historians, and the public. Due to the massive size of the Web, web archivists typically employ web crawlers for automated collection. The largest web archiving organization based on a crawling approach is the Internet Archive which strives to maintain an archive of the entire Web. 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 legal or regulatory purposes.

Collecting the Web

Web archivists generally archive all types of web content including HTML web pages, style sheets, JavaScript, images, and video. They also archive metadata about the collected resources such as access time, MIME type, and content length. This metadata is useful in establishing authenticity and provenance of the archived collection.

Methods of collection

Remote harvesting

The most common web archiving technique uses web crawlers to automate the process of collecting web pages. Web crawlers typically view web pages in the same manner that users with a browser see the Web, and therefore provide a comparatively simple method of remotely harvesting web content. Examples of web crawlers frequently used for web archiving include:

* Heritrix
* HTTrack
* [http://www.metaproducts.com/mp/Offline_Explorer_Enterprise.htm Offline Explorer]
* [http://webcurator.sourceforge.net/ Web Curator]

On-demand

There are numerous services that may be used to archive web resources "on-demand", using web crawling techniques:
* WebCite, a service specifically for scholarly authors, journal editors and publishers to permanently archive and retrieve cited Internet references (Eysenbach and Trudel, 2005).
* [http://www.archive-it.org/ Archive-It] , a subscription service, allows institutions to build, manage and search their own web archive.
* [http://www.hanzoarchives.com/ Hanzo Archives] offer commercial web archiving tools and services, implementing an archive policy for web content and enabling electronic discovery, litigation support or regulatory compliance.

Database archiving

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 [http://deeparc.sourceforge.net/ DeepArc] and [http://www.nla.gov.au/xinq/ 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

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. A transactional archiving system requires the installation of software on the web server, and cannot therefore be used to collect content from a remote website.

Examples of commercial transactional archiving software include:

* [http://www.projectcomputing.com/products/pageVault/ PageVault]
* [http://www.vignette.com/portal/site/us/menuitem.dcbb524431151aaa32189210180141a0/?vgnextoid=1e0395338521b010VgnVCM1000005610140aRCRD&vgnext-selected-menuitem=4b09bdd80b8ff1e8fb3d8010180141a0 Vignette WebCapture]

Difficulties and limitations

Crawlers

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 lies in the deep web because a crawler cannot follow a link to the results page.
* Some web servers may return a different page for a web crawler than it would for a regular browser request. This is typically done to fool search engines into sending more traffic to a website.
* 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.

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.

General limitations

Not only must web archivists deal with the technical challenges of web archiving, they must also contend with intellectual property laws. Peter Lyman (2002) 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 many countries do 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 or the Internet Archive 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 also cites on its [http://www.webcitation.org/faq FAQ] a recent lawsuit against the caching mechanism, which Google won.

Aspects of Web curation

Web curation, like any digital curation, entails:
*Collecting verifiable Web assets
*Providing Web asset search and retrieval
*Certification of the trustworthiness and integrity of the collection content
*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 suit of tools for Web Curation by International Internet Preservation Consortium:

* [http://crawler.archive.org/ Heritrix - official website] - collecting Web asset
* [http://archive-access.sourceforge.net/projects/nutch/ NutchWAX] - search Web archive collections
* [http://archive-access.sourceforge.net/projects/wayback/ Wayback (Open source Wayback Machine)] - search and navigate Web archive collections using NutchWax
* [http://webcurator.sourceforge.net/manuals.shtml Web Curator Tool] - Selection and Management of Web Collection

Other open source tools for manipulating web archives:

* [http://code.google.com/p/warc-tools/ WARC Tools] - for creating, reading, parsing and manipulating, web archives programmatically
* [http://code.google.com/p/search-tools/ Search Tools] - for indexing and searching full-text and metadata within web archives

References

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See also

* Archive
* Archive site
* Digital preservation
* Heritrix
* Internet Archive
* Library of Congress Digital Library project
* National Digital Information Infrastructure and Preservation Program
* UK Web Archiving Consortium
* Web crawling
* WebCite
* Virtual artifact

External links

* [http://www.netpreserve.org/ 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
* [http://www.iwaw.net/ International Web Archiving Workshop (IWAW)] - Annual workshop that focuses on web archiving
* [http://www.loc.gov/library/libarch-digital.html The Library of Congress, Digital Collections and Programs]
* [http://www.loc.gov/webcapture/ Library of Congress, Web Capture]
* [http://www.ifs.tuwien.ac.at/~aola/links/WebArchiving.html Web archiving bibliography] - Lengthy list of web-archiving resources
* [http://listes.cru.fr/sympa/info/web-archive Web archiving discussion list] - Used for discussing the technical, legal, and organizational aspects of web archiving
* [http://www.webarchivist.org/ WebArchivist] - Researchers that work with scholars, librarians, and archivists interested in preserving and analyzing Web resources
* Web archiving programmes:
** [http://www.boa-bw.de/ Baden-Württemberg Online Archive]
** [http://govinfo.library.unt.edu/ CyberCemetery]
** [http://www.sino.uni-heidelberg.de/dachs/ Digital Archive of Chinese Studies]
** [http://www.europarchive.org/ European Archive]
** [http://www.hanzoarchives.com/ Hanzo Archives]
** [http://www.archive.org/ Internet Archive]
** [http://www.digitalpreservation.gov The Library of Congress, National Digital Information Infrastructure and Preservation Program]
** [http://www.loc.gov/minerva/ Minerva]
** [http://netarchive.dk/ netarchive.dk]
** [http://pandora.nla.gov.au/ Pandora]
** [http://www.nationalarchives.gov.uk/preservation/archivedwebsites.htm UK Government Web Archive]
** [http://www.webarchive.org.uk/ UK Web Archiving Consortium]
** [http://warp.ndl.go.jp/ WARP]
** [http://www.webcitation.org WebCite]