"Web search technology is a huge subject, encompassing:
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networking (spidering the web),
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string and markup-language manipulation (parsing HTML)
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proprietary file formats (searching Word, Excel, PDF, etc)
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language and text-parsing (finding words & sentences in documents, stemming and other linguistic analysis),
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algorithms (finding matches, AND/OR queries, combining multiple word results)
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performance (both increasing spidering speed, and making large catalogs fast to search)
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user interface (presenting search input options, and results)
Searcharoo.net hardly touches the surface on any of these topics 
but it does attempt to introduce them with an open-source C# implementation of a search engine that you can download and use on your website."
