Browsing the World Wide Web

1. Browsing the World Wide Web

2. Browsing Service • Allows one to conveniently obtain and display information that is stored on a remote computer • A browser (like Netscape, Explorer) can: • Obtain data (text, audio, video) from remote computers as a result of a request • Display the retrieved information • Store the retrieved information • Print a copy of the data • Follow a reference Computer Networks Applications

3. Browsing vs. FTP • Both browsing and FTP provide mechanisms for retrieving data from remote computers • However, browsing: • Allow users to view data without necessarily requiring knowing the names of the individual files. • Displays the content of documents to users. • A document on one computer can point to documents stored on different computers a user can jump from one computer to another without knowing or caring about which computers are being accessed. Computer Networks Applications

4. Hypertext • Information is stored as a set of documents; • Menus (pointers) are embedded in a document in order to make them easier to understand; • The combination of text and menus is called hypertext • Note: not all documents referred by a page reside on the same computer; • Mosaic---the first browser which displayed hypertext. Computer Networks Applications

5. Hypermedia • Multimedia computer--- a computer equipped with dedicated hardware that can display pictures or play video; • Hypermedia documents---documents that may include beside text information, other types of data including pictures, audio, video; • As for textual reference, the non-textual data can reside on different computers; • World Wide Web---an example of hypermedia browsing media. Computer Networks Applications

6. Hypermedia (cont.) • Netscape, Explorer---browsers displaying hypermedia documents. • The text corresponding to a link is displayed in a different color; • To select an item, one has to click it; • When an item is selected the browser: • Obtains the document • Displays the document. Computer Networks Applications

7. Browser Functionality • A menu and a series of buttons allow a user to: • Print; • Save; • Navigate back and forth; • Find a word in a page; • View the source of a document; • Maintain a list of document bookmarks. Computer Networks Applications

8. Document address---URL • URL an acronym for Uniform Resource Locator • An URL contains: • The protocol that a browser should use to retrieve the document (usually HTTP). • The domain name (address) of the computer on which the server is running • Location and name of the document; • Ex: http://www.rutgers.edu/almaMater/almamater.shtml Computer Networks Applications

9. URL (cont.) • Not all elements in a URL are required; • If an element is not given, the browser provides a default value; • EX: • The default protocol is HTTP • The default name of a file is index.html; • In a domain address, the default computer name is www, and the default type is com. • The address “cnn” will be expanded by the browser to: “http://www.cnn.com/index.html” Computer Networks Applications

10. URL (cont.) • Note: • The vast majority of the URLs addresses call the server-computer: “www”; • However, it is not necessary---but it makes the address (and server location) easier • Moreover, a server may have a different name, and “www” is just an alias. • The name and the alias(es) correspond to the same IP address. • EX: the server “athos.rutgers.edu” with IP address 128.6.25.4 has the alias “www.cs.rutgers.edu”. Computer Networks Applications

11. How a browser works • Uses the client server paradigm: • The client is the browser program • The server: the remote HTTP server which serves requests; • A browser connects with one server at a time: • it retrieves the server address: • establishes a connection with it; • makes a request, • receives and displays the data, and • closes the connection. Computer Networks Applications

12. HTTP: Hypertext Transfer Protocol • It allows a client to request a specific item, which a server returns • HTTP requests are sent as text encoded in ASCII; • Two main operations: • GET request a document from the server • PUT (POST) sends data to the server; Computer Networks Applications

13. Browser Architecture • Because a URL can specify a different service, a browser may handle several services a browser consists of all software needed to support these services; • When a request is made, the interface (or controller) extracts the prefix, and uses it to choose the appropriate software; Computer Networks Applications

14. Conclusion • A browser integrates access to multiple Internet services into a single system. Computer Networks Applications