Google search is a Web search engine owned by Google, Inc., and is the most used search engine on the Web. Google receives several hundred million queries each day through its various services. Google search was originally developed by Larry Page and Sergey Brin in 1997.

PageRank

Google’s algorithm uses a patented system called PageRank to help rank web pages that match a given search string.

The PageRank algorithm computes a recursive score for web pages, based on the weighted sum of the PageRanks of the pages linking to them. The PageRank derives from human-generated links, and is thought to correlate well with human concepts of importance. The exact percentage of the total of web pages that Google indexes is not known, as it is very hard to actually calculate. Previous keyword-based methods of ranking search results, used by many search engines that were once more popular than Google, would rank pages by how often the search terms occurred in the page, or how strongly associated the search terms were within each resulting page. In addition to PageRank, Google also uses other secret criteria for determining the ranking of pages on result lists, reported to be a number over 200.

Search results

Google not only indexes and caches web pages but also takes “snapshots” of other file types, which include PDF, Word documents, Excel spreadsheets, Flash SWF, plain text files, online videos such as YouTube and much more. Except in the case of text and SWF files, the cached version is a conversion to (X)HTML, allowing those without the corresponding viewer application to read the file.

Users can customize the search engine, by setting a default language, using the “SafeSearch” filtering technology and set the number of results shown on each page. Google has been criticized for placing long-term cookies on users’ machines to store these preferences, a tactic which also enables them to track a user’s search terms and retain the data for more than a year. For any query, up to the first 1000 results can be shown with a maximum of 100 displayed per page.

Non-indexable Data

Despite its immense index, there is also a considerable amount of data available in online databases, which are accessible by means of queries but not by links. This so-called invisible or deep web is minimally covered by Google and other search engines and contains, for example, catalogs of libraries, official legislative documents of governments, phone books, and other content which is dynamically prepared to respond to a query.

Google optimization

Since Google is the most popular search engine, many webmasters have become eager to influence their website’s Google rankings. An industry of consultants has arisen to help websites raise their rankings on Google and on other search engines. This field, called search engine optimization, attempts to discern patterns in search engine listings, and then develop a methodology for improving rankings.

As Google’s algorithms and results have gained the trust of web users, commercial websites will profit from subverting these results by artificially inflating their rankings. Some search engine optimization firms have attempted to inflate specific Google rankings by various artifices, and thereby draw more searchers to their client’s sites. One of Google’s main challenges has been to weaken some of these attempts by reducing the ranking of sites known to use them.

Search engine optimization encompasses both “on page” factors (like body copy, title elements, H1 heading elements and image alt attribute values) and Off Page Optimization factors (like anchor text and PageRank). The general idea is to affect Google’s relevance algorithm by incorporating the keywords being targeted in various places “on page”, in particular the title element and the body copy (note: the higher up in the page, presumably the better its keyword prominence and thus the ranking). Too many occurrences of the keyword, however, cause the page to look suspect to Google’s spam checking algorithms.

Google has published guidelines for website owners who would like to raise their rankings when using legitimate optimization consultants.

Google dance

Google dance refers to the period of time when Google indices are tuned. This will often cause both a fluctuation in index size as well a significant change in a web site’s search result position. “Google Dance” also refers to the annual party at the Googleplex during the Search Engine Strategies San Jose conferences.