Chapter 9: Search
Robot ExclusionBefore getting too involved putting yourself in every search engine, remember that it isn't always a good idea to have a robot index your entire site, whether it is your own internal search engine or a public search engine. First, some pages such as programs in your cgi-bin directory don't need to be indexed. Second, many pages may be transitory, and having them indexed may result in users seeing 404 errors if they enter from a search engine. Finally, you may just not want people to enter on every single pageparticularly those pages deep within a site. So-called "deep linking" can be confusing for users entering from public search engines. Because these users start out deep in a site, they are not exposed to the home or entry page information that is often used to orient site visitors.
Probably the most troublesome aspect of search engines and automated site gathering tools such as offline browsers is that they can be used to stage a denial of service attack on a site. The basic idea of most spiders is to read pages and follow pages as fast as they can. If you tell a spider to crawl a single site as fast as it possibly can, all the requests to the crawled server may very quickly overwhelm it, causing the site to be unable to fulfill requeststhus denying services to legitimate site visitors. Fortunately, most people are not malicious in spidering, but it does happen inadvertently when a spider keeps reindexing the same dynamically generated page.
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