In This Chapter

• Why you need to care how Google works
• The importance of PageRank
• Why you want spiders visiting your site
• Understanding relevance scoring
• Google versus Yahoo! Search and MSN Search

The previous chapters include many examples of Google searches that produce thousands or even millions of matches, but the question of how Google figures out which matches are relevant hasn't been addressed. There are actually two topics here, because Google uses a formula they call PageRank to calculate the relative importance of a site -- and the pages within the site -- to the overall web, and uses a different calculation that I call a Relevance Score to calculate the relevance of a page to a given search.

Let's start with a caveat, though: the exact details of the PageRank and relevance score calculations are the crown jewel of Google's intellectual property. There are some early academic papers by the founders that explain an early version of the PageRank formula, but no-one outside the company really knows how it works today. There are so-called "search engine optimization" (or SEO) experts who claim they have the secret to Google's calculations, but the assumptions they make are based on guesses from the community, not specific details from Google.

Note: This chapter contains the most accurate information possible, but Google doesn’t disclose the details of its search engine, so you’ll want to pop over to findability.info to check for updates or news.

As a result, the information in this chapter might well be wrong.

If it is wrong, it's only going to be wrong in the nuances, however, so the basic concept of PageRank being based on inbound links and relevance being based on a formula that calculates keyword frequency and keyword usage will still steer you right, and, most importantly, will still indicate how to restructure and rethink your online presence to maximize your findability.

Google isn't the only search engine online either. I'll talk briefly about the Yahoo! and MSN search engines, competitors that obviously aren't using the Google internal PageRank formula.

The basic concepts that underlie Google's formulas are elegant, logical, and ingenious, so these other sites must be using similar calculations. If you're using proper and legitimate methods to increase the quality of your pages, the layout of your site, and the value of your site to the online community, you'll be gaining relevance points on all three search engines, not just Google.