19-04-2011, 10:23 AM
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ABSTRACT
A web search engine is a program designed to help find information stored on the World Wide Web. Search engine indexes are similar, but vastly more complex that back of the book indexes. The quality of the indexes, and how the engines use the information they contain, is what makes or breaks the quality of search results.
The vast majority of users navigate the Web via search engines. Yet searching can be the most frustrating activity using a browser. Type in a keyword or phrase, and we're likely to get thousands of responses, only a handful of which are close to what we looking for. And those are located on secondary search pages, only after a set of sponsored links or paid-for-position advertisements. Still, search engines have come a long way in the past few years.
Although most of us will never want to become experts on web indexing, knowing even a little bit about how they're built and used can vastly improve our searching skills.
This paper gives a brief introduction to the web search engines, architecture, the work process, challenges faced by search engines, discuss various searching strategies, and the recent technologies in the web mining field
INTRODUCTION
A web search engine is a program designed to help find information stored on the World Wide Web. 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 are essentially massive full-text indexes of web pages. They use regularly updated indexes to operate quickly and efficiently. The quality of the indexes, and how the engines use the information they contain, is what makes -- or breaks -- the quality of search results. Search engine indexes are similar, but vastly more complex that back-of-the-book indexes. Knowing even a little bit about how they're built and used can vastly improve the searching skills.
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. 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 search engines owned by other companies.
History:
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. More recently search engines are also coming online which utilise XML or RSS. This allows the search engine to efficiently index data about websites without requiring a complicated crawler. The websites simply provide an xml feed which the search engine indexes. XML feeds are increasingly provided automatically by weblogs or blogs. Examples of this type of search engine are feedster, with niche examples such as LjFind Search providing search services for Livejournal blogs.
THE WORKING PROCESS
The Architecture:
Search Engines for the general web do not really search the World Wide Web directly. Each one searches a database of the full text of web pages selected from the billions of web pages out there residing on servers. When we search the web using a search engine, you are always searching a somewhat stale copy of the real web page. When you click on links provided in a search engine's search results, you retrieve from the server the current version of the page.
The outline process of web search engine architecture is:
Working Process:
To find information on the hundreds of millions of Web pages that exist, a search engine employs special software robots, called spiders or Crawler, to build lists of the words found on Web sites. When a spider is building its lists, the process is called Web crawling. They find the pages for potential inclusion by following the links in the pages they already have in their database (i.e., already "know about"). They cannot think or type a URL or use judgment to "decide" to go look something up and see what's on the web about it.
If a web page is never linked to in any other page, search engine spiders cannot find it. The only way a brand new page - one that no other page has ever linked to - can get into a search engine is for its URL to be sent by some human to the search engine companies as a request that the new page be included. All search engine companies offer ways to do this.
