Google is a popular search engine that helps users find information on the internet. It crawls websites to index their content, analyzes the indexed information and stores it in vast databases, then retrieves relevant pages for user queries by ranking pages according to their algorithms. Other search engines and tools include Yahoo, Bing, subject directories that organize information by topic, metasearch engines that search multiple engines simultaneously, and specialized engines for specific subjects like health, movies or jobs.

1. CS 101
USE OF SEARCH ENGINE(S). IDENTIFYING AND EXPRESSING INFORMATION NEEDS SEARCHING AND COLLECTING
INFORMATION
BY GULSHAN KUMAR MAHESHWARI
QAU_ISLAMABAD

7. IR Attempts to find relevant documents to respond to a users request.

8. SEARCH ENGINE
• Search engine is the popular term for an information retrieval (IR) system.
• Helping people find what they’re looking for
• Starts with an “information need”
• Convert to a query
• Gets results
• It is web site that provides the facility to find the required web sites on a particular topic.
• Search engines are very powerful tools for finding information. It search the required web site and display them
to the user.
Examples:
• Google
• Yahoo
• Ask

9. SEARCH SERVICES
• Search services are organizations that maintain databases accessible through websites to help you find
information on the internet.
• Search services also maintain search engines, programs that enable you to ask questions or use keywords
to help locate information on the web.
• Search services compile their databases by using special programs called spiders —also known as crawlers,
bots (for “robots”), or agents —that crawl through the World Wide Web, following links from one web
page to another and indexing the words on that site.

10. THREE BASIC STAGES FOR A SEARCH ENGINE
1: Crawling-- where content is discovered
Crawling is where it all begins – the acquisition of data about a website. This involves scanning the site and getting a
complete list of everything on there – the page title, images, keywords it contains, and any other pages it links to – at a bare
minimum.
• A web crawler (also known as a web spider or web robot).A crawler is a program that visits Web sites and reads their pages and
other information in order to create entries for a search engine index.
2: Indexing: where it is analysed and stored in huge databases
• Indexing is the process of taking all of that data you have from a crawl, and placing it in a big database. Imagine trying to a make a
list of all the books you own, their author and the number of pages. Going through each book is the crawl and writing the list is the
index. But now imagine it’s not just a room full of books, but every library in the world. That’s pretty much a small-scale version of
what Google does.
• All of this data is stored in vast data-centres with thousands of petabytes worth of drives.

11. THREE BASIC STAGES FOR A SEARCH ENGINE
3: Ranking & Retrieval: where a user query fetches a list of relevant pages
• The last step is what you see – you type in a search query, and the search engine attempts to display the most
relevant documents it finds that match your query. This is the most complicated step, but also the most relevant to
web developers and users. It is also the area in which search engines differentiate themselves (though, there was
some evidence that Bing was actually copying some Google results). Some work with keywords, some allow you to
ask a question, and some include advanced features like keyword proximity or filtering by age of content.
• The ranking algorithm checks your search query against billions of pages to determine how relevant each
one is. This operation is so complex that companies closely guard their own ranking algorithms as patented
industry secrets.

12. QUERY
• In general, a query (noun) is a question, often required to be expressed in a formal way.
• A search engine query is a request for information that is made using a search engine. Every time a user
puts a string of characters in a search engine and presses "Enter", a search engine query is made.
• User enters into a web search engine to satisfy his or her information needs.

16. SEARCH ENGINES DIFFER IN WHAT THEY COVER
• Search engines list their results according to some kind of relevance ranking, and different search
engines use different ranking schemes. Some search engines, for instance, rank web pages according to
popularity (frequency of visits by people looking for a particular keyword), but others don’t.

17. WEB SEARCH TOOLS
Four Web Search Tools:
1. Individual Search Engines
2. Subject Directories
3. Metasearch Engines
4. Specialized Search Engines

18. 1:INDIVIDUAL SEARCH ENGINES
• An individual search engine compiles its own searchable database on the web. You search for
information by typing one or more keywords, and the search engine then displays a list of web pages, or
“hits,” that contain those keywords, ordered from most likely to least likely to contain the information
you want. Hits are defined as the sites that a search engine returns after running a keyword search.
• Examples of this kind of search engine are Ask, Bing, Google, and Yahoo!

19. 2: SUBJECT DIRECTORIES
• Unlike a search engine, a subject directory is created and maintained by human editors, not
electronic spiders, and allows you to search for information by selecting lists of categories or topics,
such as “Health and Fitness” or “Science and Technology.” Directories tend to be smaller than search
engine databases, usually indexing only the top-level pages of a website. Subject directories are best for
browsing and for searches of a more general nature.21 Examples of subject directories are Beaucoup!,
Galaxy, Google Directory, LookSmart, Open Directory Project, and Yahoo! Directory.

20. 3: METASEARCH ENGINES
• A metasearch engine allows you to search several search engines simultaneously. Metasearch engines are very
fast and can give you a good picture of what’s available across the web and where it can be found. Examples are
Clusty, Dogpile, Mamma, MetaCrawler, and Webcrawler.
4: SPECIALIZED SEARCH ENGINES
There are also specialized search engines, which help locate specialized subject matter, such as material about
movies, health, and jobs.

21. GOOGLE
Results

22. Lab activity