“It's easy to make a buck. It's a lot tougher to make a difference.” ~ Tom Brokaw ~

Types of Search Engines

Before attempting to optimise your site, it is important to have a simple understanding of the different types of search engines and their functions.

Crawlers, robot-powered
Crawler-based search engines, such as Google, have three major elements:

1. Spider (or crawler robot) – The spider travels the Internet to visit webpages. When it comes across a site, it ‘reads’ the HTML code of your home page before following any links to other pages within the site. The spider returns to the site and crawls it on a regular basis, looking for changes. Google crawls sites on the web in descending order of their rankings, meaning the highest ranked pages are crawled first and most often.

2. Index – The findings of the spider’s work are stored and catalogued in the search engine’s index. This huge resource is updated with new information following repeat visits from the spider. Sometimes even though a site has been ‘spidered’ it may not have been ‘indexed’ yet, and is therefore unavailable to those searching with the search engine. Changes to your webpages will eventually be crawled, which will affect how you are listed.

3. Software – The search engines have complex programs sitting behind their search windows that we use for searching. An algorithm is used to work through the millions or billions of pages in its index so it can find matches to the search, before ranking them in order of what it believes is most relevant.

Directories, human-powered
Directories depend on humans for their listings, rather than robots. After submitting a short description of your entire site to human-powered directories, such as Yahoo, DMOZ Open Directory and Looksmart, a human editor will consider it, and even re-write it before it is added. A good site, with good content, is generally more likely to get reviewed and added for free than a poor site. Searching the directory provides matches only in the descriptions entered. Since the directory does not automatically update itself with content from all the websites listed, changes to your webpages have no effect on your listing.

Hybrids
More and more search engines are presenting their results as a combination of crawler-based results and human-powered listings. These are known as hybrid search engines and they generally favour one type of listing over another. (eg: MSN Search is more likely to present human-powered listings from Looksmart than crawler-based results provided by Inktomi.) It is therefore important that you optimise for both types.

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