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Search Engine Basics   «Prev  Next»
Lesson 1

How Search Engines and Directories work

Up to this point in the course, you have not done any searching (unless you have tried a search with some of the sites you visited in the last module).
Now that you have been introduced to different search services and to some challenges of searching, you can begin to practice some searches.
The searching exercises in this module let you compare different categories of information retrieval services and different services in the same category.
This module will also discuss in more detail the concepts and functions of directories and search engines, including their advantages and disadvantages compared to other information retrieval service categories, how they can complement each other, and why one may be more appropriate than the other in a particular search.
An understanding of how each type of search service functions will help you to create more effective search strategies.
After completing this module, you will be able to:
  1. Describe how directories are created and organized, their advantages and limitations
  2. Describe how a search engine creates and maintains its database of sites
  3. Ask a search engine to find information with a search query
  4. Explain how a search engine's database affects your results


Click the link below to consider what makes using a search engine or directory an easy or a difficult experience.
How search engines work
Search Engine Optimization (SEO) is the activity of optimizing web pages or whole sites in order to make them search engine friendly, thus getting higher positions in search results. This tutorial explains simple SEO techniques to improve the visibility of your web pages for different search engines, especially for Google, Yahoo, and Bing.

How does a Search Engine Work?

Search engines perform several activities in order to deliver search results.
  1. Crawling: Process of fetching all the web pages linked to a website. This task is performed by a software called a crawler or a spider (or Googlebot, in case of Google).
  2. Indexing: Process of creating index for all the fetched web pages and keeping them into a giant database from where it can later be retrieved. Essentially, the process of indexing is identifying the words and expressions that best describe the page and assigning the page to particular keywords.
  3. Processing: When a search request comes, the search engine processes it, i.e., it compares the search string in the search request with the indexed pages in the database.
  4. Calculating Relevancy: It is likely that more than one page contains the search string, so the search engine starts calculating the relevancy of each of the pages in its index to the search string.
  5. Retrieving Results: The last step in search engine activities is retrieving the best matched results. Basically, it is nothing more than simply displaying them in the browser.
Search engines such as Google often update their search algorithms several times per month. When you see changes in your rankings, it is due to a new algorithm being implemented.