How do search engines work?

Searching the world wide web

The world wide web is made up of nearly 2 billion websites.

Each has its own , or web address.

You'll know the URL of some of your favourite webpages. You use this to visit these webpages.

What happens if you want to go to a webpage and you don't know the URL?

What are search engines?

A search engine is a that finds webpages on the web.

You type in the words that you want information on.

The search engine then looks for webpages that contain that information.

A search engine is a bit like a librarian.

When you go to the library, you can ask a librarian to find books on your favourite topic.

The librarian searches through an index to find the books.

The index contains key information about each book in the library.

The librarian then tells you the titles of the books that they have found.

How a search engine works

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You type the keywords or a question into the search engine
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The program searches the index for webpages that link to your keywords or question
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The program decides which pages are the most useful to you
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The program ranks (puts in order) the webpages so the most useful are at the top
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The search engine shows the webpage it has found for you

Are all search engines the same?

There are different search engines that you can use to help you find webpages. We use most search engines in a similar way.

We need to think about the words that we use in our searches. Typing in wellington will return information on:

the capital city of New Zealand
wellington boots
a type of food

By adding extra words to the search, such as Wellington, New Zealand we can get more accurate results.

Some search engines only search for certain content. They might only search for news stories, facts or images.

Other search engines are designed for children to use. These search engines do not look at pages that are unsuitable for a child.

How do search engines make an index?

A search engine makes an using a web crawler.

A web crawler is an automated program that automatically browses the web and stores information about the webpages it visits.

Every time a web crawler visits a webpage, it makes a copy of the page and adds the URL to the index.

It also adds details of the content on the page, keywords and the type of media.

When you type words into a search engine, it searches its index for matches to your words.

How do search engines order results?

Search engines use to order the list of webpages they return.

The webpages that are placed at the top of the list are usually the most useful to you. All the webpages have been visited by the search engine’s web crawlers.

So the next time you use a search engine to find information, remember that web crawlers have created an index and an algorithm was used to rank the results.

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