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
, 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
of the archived collection.
Methods of collection
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:
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 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 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
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  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:
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 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.
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.
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:
Other open source tools for manipulating web archives:
- WARC Tools - for creating, reading, parsing and manipulating, web archives programmatically
- Search Tools - for indexing and searching full-text and metadata within web archives
- Brown, A. (2006). Archiving Websites: a practical guide for information management professionals. Facet Publishing. ISBN 1-85604-553-6.
- Brügger, N. (2005). Archiving Websites. General Considerations and Strategies. The Centre for Internet Research. ISBN 87-990507-0-6.
- Day, M. (2003). "Preserving the Fabric of Our Lives: A Survey of Web Preservation Initiatives". Research and Advanced Technology for Digital Libraries: Proceedings of the 7th European Conference (ECDL) 461–472.
- Eysenbach, G. and Trudel, M. (2005). "Going, going, still there: using the WebCite service to permanently archive cited web pages". Journal of Medical Internet Research 7 (5):
- Fitch, Kent (2003). "Web site archiving - an approach to recording every materially different response produced by a website". Ausweb 03 .
- 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. Springer-Verlag. ISBN 3-540-23338-5.