Cracking the Code: How Does a Search Engine Work?

How Does a Search Engine Work?
Search engines are software that help web users search for information on the Internet. They let the Internet users find what they are looking for, by crawling the web to index pages so as to render the most relevant and the best results for the different types of web searches conducted by users. This Buzzle article tells you how search engines work.
What is a Search Engine?
By definition, an Internet search engine is an information retrieval system, which helps us find information on the World Wide Web. The Internet facilitates global sharing of information. But it is an unstructured database that needs some kind of organizing for effective retrieval of information when searched for. This information database is growing exponentially, making the task of searching for information on the web, rather difficult. This highlights the need of a tool to manage, filter, and retrieve information from this oceanic web. A search engine serves this purpose.
How Search Engines Work
Internet search engines or web search engines as they are also called, are engines that search for and retrieve information on the web. Most of them use a crawler-indexer architecture. They depend on their crawler modules.
Crawlers, also referred to as spiders, are small programs that browse the web. They are given an initial set of URLs whose pages they retrieve. They extract URLs that appear on the crawled pages and give this information to the crawler control module. The crawler module decides which pages to visit next and gives their URLs back to the crawlers.
The topics covered by different search engines vary according to the algorithms they use. Some search engines are programmed to search sites on a particular topic while crawlers in others may be visiting as many sites as possible.
The crawl control module may use the link graph of a previous crawl or use the usage patterns to help in its crawling strategy.
The indexer module extracts words from each page it visits and records its URLs. It results into a large lookup table that gives a list of URLs pointing to pages where each word occurs. The table enlists those pages, which were covered in the crawling process.
A collection analysis module is another important part of the search engine architecture. It creates a utility index. A utility index may provide access to pages of a given length or pages containing a certain number of pictures on them.
During the process of crawling and indexing, a search engine stores the pages it retrieves. They are temporarily stored in a page repository. Search engines maintain a cache of pages they visit so that retrieval of already visited pages expedites.
The query module of a search engine receives search requests from users in the form of keywords. The ranking module sorts the results.
The crawler indexer architecture has many variants. It is modified in the distributed architecture of a search engine. These search engine architectures consist of gatherers and brokers. Gatherers collect indexing information from web servers while brokers give the indexing mechanism and the query interface. Brokers update indices on the basis of the information received from gatherers and other brokers. They can filter information. Many search engines of today use this type of architecture.
Search Engines and Page Ranking
When we submit a query to a search engine, results are displayed in a particular order. Most of us tend to visit the pages in the top order and ignore those beyond the first few. This is because we consider the top few pages to bear the most relevance to our query. So all are interested in ranking their pages in the first ten results of a search engine.
The words you specify in the query interface of a search engine are the keywords which are sought by search engines. The engines present a list of pages relevant to the queried keywords. During this process, search engines retrieve those pages which have frequent occurrences of the keywords. They look for interrelationships between keywords. The location of keywords is also considered while ranking pages that contain them. Keywords that occur in the page titles or in the URLs are given greater weight. A page having links that point to it makes it more popular. If many sites link to a page, it is regarded as valuable and more relevant.
There is a ranking algorithm that every search engine uses. The algorithm is a computerized formula devised to match relevant pages with a user query. Each search engine may have a different ranking algorithm, which parses the pages in the engine's database to determine relevant responses to search queries. Different search engines index information differently. Because of this, a particular query put to two distinct search engines may fetch pages in a different order or even retrieve different pages. The keyword as well as the website's popularity are factors which contribute to determining relevance. The click-through popularity of a site is another determinant of its rank. This popularity is the measure of how often the site is visited.
Webmasters try to trick search engine algorithms to increase the rankings of their websites. The tricks include populating the home page of a site with keywords or the use of meta-tags to deceive ranking strategies. But search engines are smart enough. They keep revising their algorithms and counter-program their systems so that we as searchers don't fall prey to illegal or unethical practices of webmasters.
If you are a serious searcher, understand that even the pages beyond the first few may have well-written content. However, good search engines give every good web page the position it deserves. The competition is tough, and one has to be the best to rank in the top few search engine results. This is the case with at least good search engines, which are obviously also the most used. Due to increasing competition on the web, and with the search engines implementing intelligent ranking strategies, users today are assured of finding the most relevant and the best pages for their search queries.