Search engines are software systems that find web pages that match a search query, usually a set of words. They use programs known as spiders or crawlers to systematically scour the World Wide Web for information that matches a query. The result is displayed as a list of web pages in a form commonly known as a search engine results page (SERP). Search engines are the primary source of most Internet content, and they are also used in corporate environments to find and analyze data sets that may be too large or complex for manual processing.
The most important task of any search engine is indexing, which is the process of associating words and other definable tokens found on web pages with their domain names and HTML-based fields. These associations are then stored in a database and made available for searching.
Once a search engine has indexed all the pages that contain the keywords in a query, it can display the results in an ordered list for end-users. The order is based on the relevance of the results to the query, as determined by its algorithm. The results can include links to websites, images, news articles, videos or other files.
A common way to refine a search query is by using the boolean operators AND, OR and NOT to define a set of search terms that the search engine should look for in all of its records. Search engines typically search for the exact word or phrase that was entered, so putting words in quotation marks around the terms makes them look for only those items.
Search engines have a huge number of tools to help them deal with all kinds of content. They can handle text, XML, JSON, CSV, PDF, Office docs, images/video, GIS/Spatial and even custom formats. They can also quickly sort and score objects in a record set to create a retrieval set, then do a number of things with that set like on-the-fly regression analysis or aggregation.
Many of these search engine techniques require significant calculation at indexing time, when the search engine crawls new and changed web pages. This means that they cannot be implemented at search time, which can slow down the overall search process.
There are a few basic search engine techniques that all users should be aware of to get the best results from a search engine. They can include searching for word stems and phrases, using boolean operators and looking for proximity searches. A more advanced feature is the concept-based searching, which is a search method that looks at context to find useful results. It can be done with a tool called Lucene, which is integrated into most modern search engines. There are also specialized search engines for different types of media, such as video, music and images. These tools can be accessed from the links at the top of most search engines’ web pages. In addition, there are a variety of plugins and applications that can be used to enhance the functionality of a search engine.