4. Web Search Tools: Web Search Engines
Sometimes browsing isn't the best approach, particularly if you need rather specific information. Many people have used a web search engine at some point in their life.
Think of the Web as a book. A topic you're interested in may be in multiple places within that book. You can flip through it or you can go to index to look up your topic and find where it's mentioned. This is how a web search engine, or web index, works. It looks at all of the pages to which it has access to see where your term occurs.
Characteristics of web search engines:
|Size||They are huge. For example, Google, Yahoo!, and Bing all index billions of web pages. Want to see how things have changed over time? Check out Search Engine Watch's Search Engine Sizes page.|
|Built by||They are built and maintained by a software program called a robot, spider or crawler. This program roams the Web, collects information from pages, and stores this information in a database called its index.|
|Contents||The Index contains all of the words on each page that is included in it. This allows you to find rather obscure information, but also makes it harder to get good results for many searches.|
|Coverage||Each index has some unique content, and no one index covers all of the Web.|
|When||Ever have a web page in your search results that no longer exists or seems to not cover your search term(s)? This is because web pages can change quickly or even be deleted, while web search engines may take some time to catch up to these changes. What a search engine thinks is on a web page is really just a snapshot in time.|
Compare the results (types of pages, number of items, etc.) for a search for the word cantaloupes in the following search engines (clicking the link results in search being performed). You may notice each search engine has a different way of displaying results, which results float to the top, and how many results are found.
Some web search engines offer categorization of results - you can specify an area into which your topic falls. Many search engines let you limit results to news, images, or other categories.
Most web search engines choose one (or both) of these methods for ordering your search results:
- An algorithm is used to determine relevancy. This is a mathematical formula that takes into account factors such as number of times words appear, where words appear, and possibly other factors the search engine programmers deem important.
- Popular sites, whether those that see a lot of traffic or those the programmers deem as important, will often be nearer the top.
You may notice at most a few pages showing per site. Some sites cluster results from the same site. Examples:
View the Google Basics video.