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.
Since web sites are often copyrighted, web archiving has to consider legal and social issues. Due to the global nature of a web environment, complex issues arise.
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 as 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 is the Internet Archive’s web crawler that was specially designed for web archiving. It is open-sourceed and written in Java. The main interface is accessible using a web browser, containing a command-line tool that can optionally be used to initiate crawls.
Heritrix was developed jointly by Internet Archive and the Nordic national libraries on specifications written in early 2003. The first official release was in January 2004, and since then, has continually improved by members of the Internet Archive and other interested third parties.
A number of organizations and national libraries are using Heritrix, among them:
HTTrack is a free and open source Web crawler and offline browser, developed by Xavier Roche and licensed under the GNU General Public License, that allows one to download World Wide Web sites from the Internet to a local computer. By default, HTTrack arranges the downloaded site by the original site's relative link-structure. The downloaded (or "mirrored") website can be browsed by opening a page of the site in a browser.
HTTrack can also update an existing mirrored site and resume interrupted downloads. HTTrack is fully configurable by options and by filters (include/exclude), and has an integrated help system. There is a basic command line version and two GUI versions (WinHTTrack and WebHTrack); the former can be part of scripts and cron jobs.
There are numerous services that may be used to archive web resources "on-demand," using web crawling techniques:
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. 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:
Web archives which rely on web crawling as their primary means of collecting the Web are influenced by the difficulties of web crawling:
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.
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 FAQ a recent lawsuit against the caching mechanism, which Google won.
Web curation, like any digital curation, entails:
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:
Other open source tools for manipulating web archives:
The Internet Archive (IA) is a nonprofit organization dedicated to building and maintaining a free and openly accessible online digital library, which includes an archive of the World Wide Web. With offices located in the Presidio in San Francisco, California, and data centers in San Francisco, Redwood City, and Mountain View, CA, the archive includes "snapshots of the World Wide Web" (archived copies of pages, taken at various points in time), software, movies, books, and audio recordings. To ensure the stability and endurance of the Internet Archive, its collection is mirrored at the Bibliotheca Alexandrina in Egypt, so far the only library in the world with a mirror. The IA makes its collections available at no cost to researchers, historians, and scholars. It is a member of the American Library Association and is officially recognized by the State of California as a library.
All links retrieved August 10, 2013.
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