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Kinds of Search Engines and Directories

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Web directories

Web directories (also known as indexes, Web indexes or catalogues) are broken down into categories and subcategories and are good for broad searches of established sites. For example, if you are looking for information on the environment but are not sure how to phrase a potential topic on holes in the ozone, you could try browsing through the Open Directory Project's categories. In its "Science" category, there is a subcategory of "Environment" that has over twenty subcategories listed. One of those subcategories is "Global Change" and this includes the "Ozone Layer" category. The "Ozone Layer" category has over twenty-five references, including a FAQ site. Those references can help you determine the key terms to use for a more focused search.

Search engines

Search engines ask for keywords or phrases and then search the Web for results. Some search engines look only through page titles and headers. Others look through documents, using Google, which can search PDFs. Many search engines now include some directory categories as well (such as Yahoo).

Metasearch engines

These (e.g., Dogpile , Mamma , and Metacrawler ) search other search engines and often search smaller, less well-known search engines and specialized sites. These search engines are good for doing large, sweeping searches of what information is out there.

A few negatives are associated with metasearch engines. First, most metasearch engines will only let you search basic terms, so there are no Boolean operators or advanced search options. Second, many metasearch engines pull from pay-per-click advertisers, so the results you get may primarily be paid advertising and not the most valid results on the Web.