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How Google Search Works & Search Algorithms

Posted by on in Search Engines
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For a typical query, there are thousands, even millions, of webpages with potentially relevant information.

So, how does Google figure out what to show in your search results? Well, the journey starts before you even type your search…

How Search organizes information

Before you search, web crawlers gather information from across hundreds of billions of webpages and organize it in the Search index.

The fundamentals of Search

The crawling process begins with a list of web addresses from past crawls and sitemaps provided by website owners. As our crawlers visit these websites, they use links on those sites to discover other pages. The software pays special attention to new sites, changes to existing sites and dead links. Computer programs determine which sites to crawl, how often and how many pages to fetch from each site.

We offer webmaster tools to give site owners granular choices about how Google crawls their site: they can provide detailed instructions about how to process pages on their sites, can request a recrawl or can opt out of crawling altogether using a file called “robots.txt”. Google never accepts payment to crawl a site more frequently — we provide the same tools to all websites to ensure the best possible results for our users.

Finding information by crawling

The web is like an ever-growing library with billions of books and no central filing system. We use software known as web crawlers to discover publicly available webpages. Crawlers look at webpages and follow links on those pages, much like you would if you were browsing content on the web. They go from link to link and bring data about those webpages back to Google’s servers.

Organizing information by indexing

When crawlers find a webpage, our systems render the content of the page, just as a browser does. We take note of key signals — from keywords to website freshness — and we keep track of it all in the Search index.

The Google Search index contains hundreds of billions of webpages and is well over 100,000,000 gigabytes in size. It’s like the index in the back of a book — with an entry for every word seen on every web page we index. When we index a web page, we add it to the entries for all of the words it contains.

With the Knowledge Graph, we’re continuing to go beyond keyword matching to better understand the people, places and things you care about. To do this, we not only organize information about webpages but other types of information too. Today, Google Search can help you search text from millions of books from major libraries, find travel times from your local public transit agency, or help you navigate data from public sources like the World Bank.

How Search algorithms work

You want the answer, not billions of webpages, so Google ranking systems sort through the hundreds of billions of webpages in our Search index to give you useful and relevant results in a fraction of a second.

These ranking systems are made up of a series of algorithms that analyze what it is you are looking for and what information to return to you. And as we’ve evolved Search to make it more useful, we’ve refined our algorithms to assess your searches and the results in finer detail to make our services work better for you.

Here are some of the ways Google uses Search algorithms to return useful information from the web:

Analyzing your words

Understanding the meaning of your search is crucial to returning good answers. So to find pages with relevant information, our first step is to analyze what the words in your search query mean. We build language models to try to decipher what strings of words we should look up in the index.

This involves steps as seemingly simple as interpreting spelling mistakes, and extends to trying to understand the type of query you’ve entered by applying some of the latest research on natural language understanding. For example, our synonym system helps Search know what you mean, even if a word has multiple definitions. This system took over five years to develop and significantly improves results in over 30% of searches across languages.

We also try to understand what category of information you are looking for. Is it a very specific search or a broad query? Are there words such as “review” or “pictures” or “opening hours” that indicate a specific information need behind the search? Are you searching for trending keywords that imply you want content published that day? Or are you searching for a nearby business and want local info?

Matching your search

Next, we look for webpages with information that matches your query. When you search, at the most basic level, our algorithms look up your search terms in the index to find the appropriate pages. They analyze how often and where those keywords appear on a page, whether in titles or headings or in the body of the text.

As well as matching keywords, algorithms look for clues to measure how well potential search results give users what they are looking for. When you search for “dogs” you likely don’t want a page with the word “dogs” on it hundreds of times. We try to figure out if the page contains an answer to your query and doesn’t just repeat your query. So Search algorithms analyze whether the pages include relevant content — such as pictures of dogs, videos, or even a list of breeds. Finally, we check to see if the page is written in the same language as your question in order to prioritize pages in your preferred language.

Ranking useful pages

For a typical query, there are thousands, even millions, of webpages with potentially relevant information. So to help rank the best pages first, we also write algorithms to evaluate how useful these webpages are.

These algorithms analyze hundreds of different factors to try to surface the best information the web can offer, from the freshness of the content, to the number of times your search terms appear and whether the page has a good user experience. In order to assess trustworthiness and authority on its subject matter, we look for sites that many users seem to value for similar queries. If other prominent websites on the subject link to the page, that’s a good sign the information is high quality.

There are many spammy sites on the web that try to game their way to the top of search results through techniques like repeating keywords over and over or buying links that pass PageRank. These sites provide a very poor user experience and may even harm or mislead Google’s users. So we write algorithms to identify spam and remove sites that violate Google’s webmaster guidelines from our results.

Considering context

Information such as your location, past search history and Search settings all help us to tailor your results to what is most useful and relevant for you in that moment.

We use your country and location to deliver content relevant for your area. For instance, if you’re in Chicago and you search “football”, Google will most likely show you results about American football and the Chicago Bears first. Whereas if you search “football” in London, Google will rank results about soccer and the Premier League higher. Search settings are also an important indicator of which results you’re likely to find useful, such as if you set a preferred language or opted in to SafeSearch (a tool that helps filter out explicit results).

In some instances, we may also personalize your results using information about your recent Search activity. For instance, if you search for “Barcelona” and recently searched for “Barcelona vs Arsenal”, that could be an important clue that you want information about the football club, not the city. You can control what search activity is used to improve your Search experience, including adjusting what data is saved to your Google account, at myaccount.google.com.

Returning the best results

Before we serve your results, we evaluate how all the relevant information fits together: is there only one topic among the search results, or many? Are there too many pages focusing on one narrow interpretation? We strive to provide a diverse set of information in formats that are most helpful for your type of search. And as the web evolves, we evolve our ranking systems to deliver better results for more queries.

Useful responses take many forms

Larry Page once described the perfect search engine as understanding exactly what you mean and giving you back exactly what you want. Over time, our testing has consistently showed that users want quick answers to their queries. We have made a lot of progress on delivering you the most relevant answers, faster and in formats that are most helpful to the type of information you are seeking.

If you are searching for the weather, you most likely want the weather forecast on the results page, not just links to weather sites. Or directions: if your query is “Directions to San Francisco airport”, you want a map with directions, not just links to other sites. This is especially important on mobile devices where bandwidth is limited and clicking between sites can be slow.

Thousands of engineers and scientists are hard at work refining our algorithms and building useful new ways to search. You can find some of our Search innovations below. With some 1600 improvements to Google Search in 2016 alone, these are just a sample of some of the ways we have been making Search better and better over time.

Answers from the Knowledge Graph

e.g. How tall is the Eiffel Tower?

In 2012, we launched the Knowledge Graph, our database of more than one billion real-world people, places and things with over 50 billion facts and connections among them. The world is made of real things, not just text strings. So we built the Knowledge Graph to show how things are connected. You can get quick answers to questions like “What is the Eiffel Tower?”, “How tall is it?”, “When was it first opened?” and then click to explore across the web.


Directions and traffic

e.g. Directions to O’Hare airport

It was always pretty obvious that when people searched on Google for an address — for example “Bushwood road” — they didn’t want a link to websites mentioning this street. They most likely wanted to know where it was and how to get there. So, we built a map that was clickable and draggable, making it super easy to explore.


Direct answers

e.g. Sundance Showtimes

Sometimes you want direct answers for certain queries so we team up with businesses that can deliver the information and services you are looking for and license their content to provide useful responses right on the Search results page. For instance, if you’re looking for the showtimes of movies at your local cinema, we partner with data providers that have up to date and reliable information about when films are showing in your area and with ticketing service providers to help you buy tickets. This is also how we can bring you the weather forecast and sports scores directly on the Search page.

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Featured snippets

e.g. When was the 21st amendment passed?

When you ask Google a question, our goal is to help you find the answer quickly and easily. Featured snippets help provide quick answers to questions by drawing attention to programmatically generated snippets from websites that our algorithms deem relevant to the specific question being asked. All Featured Snippets include a snippet of information quoted from a third party website, plus a link to the page, the page title and URL.

Featured snippets

Rich lists

e.g. Famous female astronomers

The best answer to your question is not always a single entity, but a list or group of connected people, places or things. So when you search for [California lighthouses] or [famous female astronomers], we’ll show you a list of these things across the top of the page. By combining our Knowledge Graph with the collective wisdom of the web, we can even provide lists like [best action movies of 2016] or [things to do in Rome]. If you click on an item, you can then explore the result more deeply on the web.

rich list

Answers before you have to ask

People expect information at their fingertips. That’s why the Google app on your smartphone incorporates shortcuts and a feed of useful information right onto the homescreen. This gives you access to in-depth experiences across sports, dining, entertainment and weather without having to type out a query.

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Evolving to meet the ever-changing web

The web is constantly evolving, with hundreds of new webpages published every second. That’s reflected in the results you see in Google Search: we constantly recrawl the web to index new content. Depending on your query, some results pages change rapidly, while others are more stable. For example, when you’re searching for the latest score of a sports game we have to perform up-to-the-second updates, while results about a historical figure may remain static for years at a time.

Today, Google handles trillions of searches each year. Every day, 15% of the queries we process are ones we’ve never seen before. Building Search algorithms that can serve the most useful results for all these queries is a complex challenge that requires ongoing quality testing and investment.

Source: This article was published google.com

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