Search engine (computing)
 | This page or section may contain link spam masquerading as content. |
A search engine is a program designed to help find information stored on a computer system such as the World Wide Web, or a personal computer. The search engine allows one to ask for content meeting specific criteria (typically those containing a given word or phrase) and retrieves a list of references that match those criteria. Search engines use regularly updated indexes to operate quickly and efficiently. Without further qualification, search engine usually refers to a Web search engine, which searches for information on the public Web. Other kinds of search engine are enterprise search engines, which search on intranets, personal search engines, which search individual personal computers, and mobile search engines such as Upsnap.
Some search engines also mine data available in newsgroups, large databases, or open directories like DMOZ.org. Unlike Web directories, which are maintained by human editors, search engines operate algorithmically. Most web sites which call themselves search engines, are actually front ends to other search engines owned by other companies. The typical user will often not know which underlying search engine they are using.
History
| Timeline | ||
|---|---|---|
| note: "Launch" refers only to web availability of original crawl-based web search engine results. | ||
| Year | Engine | Event |
| 1993 | Aliweb | Launch |
| 1994 | WebCrawler | Launch |
| 1994 | Lycos | Launch |
| 1995 | AltaVista | Launch (part of DEC) |
| 1995 | Excite | Launch |
| 1996 | Inktomi | Founded |
| 1996 | Ask Jeeves | Founded |
| 1997 | Northern Light | Launch |
| 1998 | Launch | |
| 1999 | AlltheWeb | Launch |
| 2000 | Teoma | Founded |
| 2004 | Yahoo! Search | Final launch (first original results) |
| 2004 | MSN Search | Beta launch |
| 2005 | MSN Search | Final launch |
The first Web search engine was "Wandex", a now-defunct index collected by the World Wide Web Wanderer, a web crawler developed by Matthew Gray at MIT in 1993. Another very early search engine, Aliweb, also appeared in 1993, and still runs today. The first "full text" crawler-based search engine was WebCrawler, which came out in 1994. Unlike its predecessors, it let users search for any word in any web page, which became the standard for all major search engines since. It was also the first one to be widely known by the public. Also in 1994 Lycos (which started at Carnegie Mellon University) came out, and became a major commercial endeavor.
Soon after, many search engines appeared and vied for popularity. These included Excite, Infoseek, Inktomi, Northern Light, and AltaVista. In some ways they competed with popular directories such as Yahoo!. Later, the directories integrated or added on search engine technology for greater functionality.
Search engines were also known as some of the brightest stars in the Internet investing frenzy that occurred in the late 1990s. Several companies entered the market spectacularly, recording record gains during their initial public offerings. Some have taken down their public search engine, and are marketing enterprise-only editions, such as Northern Light.
Before the advent of the Web, there were search engines for other protocols or uses, such as the Archie search engine for anonymous FTP sites and the Veronica search engine for the Gopher protocol.
Around 2001, the Google search engine rose to prominence. Its success was based in part on the concept of link popularity and PageRank. How many other web sites and web pages link to a given page is taken into consideration with PageRank, on the premise that good or desirable pages are linked to more than others. The PageRank of linking pages and the number of links on these pages contribute to the PageRank of the linked page. This makes it possible for Google to order its results by how many web sites link to each found page. Google's minimalist user interface was very popular with users, and has since spawned a number of imitators.
Google and most other web engines utilize not only PageRank but more than 150 criteria to determine relevancy. The algorithm "remembers" where it has been and indexes the number of cross-links and relates these into groupings. PageRank is based on citation analysis that was developed in the 1950s by Eugene Garfield at the University of Pennsylvania. Google's founders cite Garfield's work in their original paper. In this way virtual communities of webpages are found. Teoma's search technology uses a communities approach in its ranking algorithm. NEC Research Institute has worked on similar technology. Web link analysis was first developed by Dr. Jon Kleinberg and his team while working on the CLEVER project at IBM's Almaden research lab. Google is the most popular search engine at this moment in time.
Yahoo Search
In 2002, Yahoo! acquired Inktomi and in 2003, Yahoo! acquired Overture, which owned AlltheWeb and AltaVista. Despite owning its own search engine, Yahoo initially kept using Google to provide its users with search results on its main web site Yahoo.com. However, in 2004, Yahoo! launched its own search engine based on the combined technologies of its acquisitions and providing a service that gave pre-eminence to the Web search engine over the directory.
Microsoft
The most recent major search engine is MSN Search, owned by Microsoft, which previously relied on others for its search engine listings. In 2004 it debuted a beta version of its own results, powered by its own web crawler (called msnbot). In early 2005 it started showing its own results live. This was barely noticed by average users unaware of where results come from, but was a huge development for many webmasters, who seek inclusion in the major search engines.
At the same time, Microsoft ceased using results from Inktomi, now owned by Yahoo.
This meant the market was now dominated by Google, Yahoo, and Microsoft. The other large (self described) search engines tend to be "portals" that merely show the results another company's search engine (like MSN Search used to do). The other "true" search engines (those that provide their own results), like GigaBlast, have vastly less market presence than the big three. However, since site usage is proprietary information, it's often difficult to determine which sites are most popular.
Challenges faced by search engines
- The web is growing much faster than any present-technology search engine can possibly index (see distributed web crawling).
- Many web pages are updated frequently, which forces the search engine to revisit them periodically.
- The queries one can make are currently limited to searching for key words, which may result in many false positives.
- Dynamically generated sites may be slow or difficult to index, or may result in excessive results from a single site.
- Many dynamically generated sites are not indexable by search engines; this phenomenon is known as the invisible web.
- Some search engines do not order the results by relevance, but rather according to how much money the sites have paid them.
- Some sites use tricks to manipulate the search engine to display them as the first result returned for some keywords. This can lead to some search results being polluted, with more relevant links being pushed down in the result list.
How search engines work
A search engine operates, in the following order
- Crawling
- Deep Crawling Depth-first search (DFS)
- Fresh Crawling Breadth-first search (BFS)
- Indexing
- Searching
Web search engines work by storing information about a large number of web pages, which they retrieve from the WWW itself. These pages are retrieved by a web crawler (sometimes also known as a spider) — an automated web browser which follows every link it sees. The contents of each page are then analyzed to determine how it should be indexed (for example, words are extracted from the titles, headings, or special fields called meta tags). Data about web pages is stored in an index database for use in later queries. Some search engines, such as Google, store all or part of the source page (referred to as a cache) as well as information about the web pages, whereas some store every word of every page it finds, such as AltaVista. This cached page always holds the actual search text since it is the one that was actually indexed, so it can be very useful when the content of the current page has been updated and the search terms are no longer in it. This problem might be considered to be a mild form of linkrot, and Google's handling of it increases usability by satisfying user expectations that the search terms will be on the returned web page. This satisfies the principle of least astonishment since the user normally expects the search terms to be on the returned pages. Increased search relevance makes these cached pages very useful, even beyond the fact that they may contain data that may no longer be available elsewhere.
When a user comes to the search engine and makes a query, typically by giving key words, the engine looks up the index and provides a listing of best-matching web pages according to its criteria, usually with a short summary containing the document's title and sometimes parts of the text. Most search engines support the use of the boolean terms AND, OR and NOT to further specify the search query. An advanced feature is proximity search, which allows you to define the distance between keywords.
The usefulness of a search engine depends on the relevance of the results it gives back. While there may be millions of Web pages that include a particular word or phrase, some pages may be more relevant, popular, or authoritative than others. Most search engines employ methods to rank the results to provide the "best" results first. How a search engine decides which pages are the best matches, and what order the results should be shown in, varies widely from one engine to another. The methods also change over time as Internet usage changes and new techniques evolve.
Most web search engines are commercial ventures supported by advertising revenue and, as a result, some employ the controversial practice of allowing advertisers to pay money to have their listings ranked higher in search results.
The vast majority of search engines are run by private companies using proprietary algorithms and closed databases, the most popular currently being Google, MSN Search, and Yahoo! Search. However, Open source search engine technology does exist, such as ht://Dig, Nutch, Senas, Egothor, OpenFTS, DataparkSearch and many others. Mozdex.com aims to be the first publicly-available web search server using this technology.
See also
- Data mining
- History of the Internet
- List of search engines
- Metasearch engine
- Search engine optimization
- Search engine spammer
- Web indexing
- Search marketing
- Local search
External links
- On Search, the Series, Tim Bray, 2003 — A series of essays on search engine techniques.
- "How to Search and Find Whatever is Most Important to You", using Google as an example, by Alex Linsker, 2005.