Web archiving

From Wikipedia, the free encyclopedia

"Web Archive" redirects here. For the Safari format of the same name, see Webarchive.

Web archiving is the process of collecting portions of the 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.

Contents

[edit] 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.

[edit] Methods of collection

[edit] 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:

[edit] 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).
  • Archive-It, a subscription service, allows institutions to build, manage and search their own web archive
  • hanzo:web is a personal web archiving service created by Hanzo Archives that can archive a single web resource, a cluster of web resources, or an entire website, as a one-off collection, scheduled/repeated collection, an RSS/Atom feed collection or collect on-demand via Hanzo's open API.
  • Spurl.net is a free on-line bookmarking service and search engine that allows users to save important web resources.

[edit] 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 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.

[edit] 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:

[edit] Difficulties and limitations

[edit] 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.

[edit] 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." Some web archives that are made publicly accessible like WebCite's or the Internet Archive’s 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 FAQ a recent lawsuit against the caching mechanism, which Google won.

[edit] References

[edit] See also

[edit] External links