Invisible web is the portion of the web which is not indexed by search engines like google or yahoo etc. Invisible web is also called deep web, hidden web or dark web. Mike Bergman coined the term firstly by saying that searching on the Internet today can be compared to dragging a net across the surface of the ocean; a great deal may be caught in the net, but there is a wealth of information that is deep and therefore missed. Most of the Web's information is buried far down on dynamically generated sites, and standard search engines do not find it. Traditional search engines cannot "see" or retrieve content in the deep Web – those pages do not exist until they are created dynamically as the result of a specific search. The deep Web is several orders of magnitude larger than the surface Web.
Size of the deep web, in 2000, believed to be as large as approximately 7,500 terabytes of data and 550 billion individual documents. Estimates based on extrapolations from a study done at University of California, Berkeley speculate that the deep Web consists of about 91,000 terabytes. By contrast, the surface Web (which is easily reached by search engines) is only about 167 terabytes; the Library of Congress, in 1997, was estimated to have 3,000 terabytes.
However, keeping in view the vast amount of information deep web offers specialized techniques are being adopted by the serach engines to index information that is not available on the surface web. Following is a list of top 10 search engines which may proved to be useful if you have information hunt on your mind.
1. Infomine
Infomine has been built by a pool of libraries in the United States. Some of them are University of California, Wake Forest University, California State University, and the University of Detroit. Infomine ‘mines’ information from databases, electronic journals, electronic books, bulletin boards, mailing lists, online library card catalogs, articles, directories of researchers, and many other resources.
You can search by subject category and further tweak your search using the search options. Infomine is not only a standalone search engine for the Deep Web but also a staging point for a lot of other reference information. Check out its Other Search Tools and General Reference links at the bottom.
2. The WWW Virtual Library
This is considered to be the oldest catalog on the web and was started by started by Tim Berners-Lee, the creator of the web. So, isn’t it strange that it finds a place in the list of Invisible Web resources? Maybe, but the WWW Virtual Library lists quite a lot of relevant resources on quite a lot of subjects. You can go vertically into the categories or use the search bar. The screenshot shows the alphabetical arrangement of subjects covered at the site.
3. Intute
Intute is UK centric, but it has some of the most esteemed universities of the region providing the resources for study and research. You can browse by subject or do a keyword search for academic topics like agriculture to veterinary medicine. The online service has subject specialists who review and index other websites that cater to the topics for study and research.
Intute also provides free of cost over 60 free online tutorials to learn effective internet research skills. Tutorials are step by step guides and are arranged around specific subjects.4. Complete Planet
For a really effective Deep Web search, try out the Advanced Search options where among other things, you can set a date range.
5. Infoplease
Infoplease is an information portal with a host of features. Using the site, you can tap into a good number of encyclopedias, almanacs, an atlas, and biographies. Infoplease also has a few nice offshoots like Factmonster.com for kids and Biosearch, a search engine just for biographies.
6. DeepPeep
DeepPeep aims to enter the Invisible Web through forms that query databases and web services for information. Typed queries open up dynamic but short lived results which cannot be indexed by normal search engines. By indexing databases, DeepPeep hopes to track 45,000 forms across 7 domains.
The domains covered by DeepPeep (Beta) are Auto, Airfare, Biology, Book, Hotel, Job, and Rental. Being a beta service, there are occasional glitches as some results don’t load in the browser.7. IncyWincy
IncyWincy is an Invisible Web search engine and it behaves as a meta-search engine by tapping into other search engines and filtering the results. It searches the web, directory, forms, and images. With a free registration, you can track search results with alerts.
8. DeepWebTech
DeepWebTech gives you five search engines (and browser plugins) for specific topics. The search engines cover science, medicine, and business. Using these topic specific search engines, you can query the underlying databases in the Deep Web.
9. Scirus
Scirus has a pure scientific focus. It is a far reaching research engine that can scour journals, scientists’ homepages, courseware, pre-print server material, patents and institutional intranets.
10. TechXtra
TechXtra concentrates on engineering, mathematics and computing. It gives you industry news, job announcements, technical reports, technical data, full text eprints, teaching and learning resources along with articles and relevant website information.
Just like general web search, searching the Invisible Web is also about looking for the needle in the haystack. Only here, the haystack is much bigger. The Invisible Web is definitely not for the casual searcher. It is a deep but not dark because if you know what you are searching for, enlightenment is a few keywords away.
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