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Disclaimer:This presentation is prepared by trainees of baabtra as a part of mentoring program. This is not official document of baabtra –Mentoring PartnerBaabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt . Ltd
WWW History
• 1989-1990 – Tim Berners-Lee invents the World Wide Web at CERN– Means for transferring text and graphics
simultaneously– Client/Server data transfer protocol• Communication via application level protocol• System ran on top of standard networking
infrastructure
– Text mark up language• Not invented by Bernes-Lee• Simple and easy to use• Requires a client application to
render text/graphics
What Is the World Wide Web? The world wide web (web) is a network of
information resources. The web relies on three mechanisms to make these resources readily available to the widest possible audience:
1. A uniform naming scheme for locating resources on the web (e.g., URIs).
2. Protocols, for access to named resources over the web (e.g., HTTP).
3. Hypertext, for easy navigation among resources (e.g., HTML).
TYPES OF WEB
• Public web
• Invisible web/deep web
WWW Structure• Clients use browser application to send URIs via HTTP
to servers requesting a Web page• Web pages constructed using HTML and consist of
text, graphics, sounds plus embedded files• Servers respond with requested Web page• Client’s browser renders Web page returned by
server– Page is written using HTML– Displaying text, graphics and sound in browser– Writing data as well
• The entire system runs over standard networking protocols (TCP/IP, DNS,…)
Standard Generalized Markup Language (SGML)
• Based on GML (generalized markup language), developed by IBM in the 1960s
• An international standard (ISO 8879:1986) defines how descriptive markup should be embedded in a document
• Gave birth to the extensible markup language (XML), W3C recommendation in 1998
SGML Components
SGML documents have three parts:• Declaration: specifies which characters and
delimiters may appear in the application• DTD/ style sheet: defines the syntax of markup
constructs• Document instance: actual text (with the tag) of the
documentsMore info could be found:
http://www.W3.Org/markup/SGML
HTML Background
• HTML was originally developed by Tim Berners-Lee while at CERN, and popularized by the Mosaic browser developed at NCSA.
• The Web depends on Web page authors and vendors sharing the same conventions for HTML. This has motivated joint work on specifications for HTML.
• HTML standards are organized by W3C : http://www.w3.org/MarkUp/
HTML FunctionalitiesHTML gives authors the means to:• Publish online documents with headings, text, tables,
lists, photos, etc– Include spread-sheets, video clips, sound clips,
and other applications directly in their documents• Link information via hypertext links, at the click of a
button• Design forms for conducting transactions with
remote services, for use in searching for information, making reservations, ordering products, etc
Sample Webpage
Sample Webpage HTML Structure
<HTML>
<HEAD>
<TITLE>The title of the webpage</TITLE> </HEAD>
<BODY> <P>Body of the webpage
</BODY>
</HTML>
HTML Structure
• An HTML document is divided into a head section (here, between <HEAD> and </HEAD>) and a body (here, between <BODY> and </BODY>)
• The title of the document appears in the head (along with other information about the document)
• The content of the document appears in the body. The body in this example contains just one paragraph, marked up with <P>
HTML Hyperlink
<a href="relations/alumni">alumni</a>• A link is a connection from one Web resource to
another• It has two ends, called anchors, and a direction• Starts at the "source" anchor and points to the
"destination" anchor, which may be any Web resource (e.g., an image, a video clip, a sound bite, a program, an HTML document)
Resource Identifiers
URI: Uniform Resource Identifiers• URL: Uniform Resource Locators• URN: Uniform Resource Names
Introduction to URIs
Every resource available on the Web has an address that may be encoded by a URI
URIs typically consist of three pieces:• The naming scheme of the mechanism used to
access the resource. (HTTP, FTP)• The name of the machine hosting the resource• The name of the resource itself, given as a path
URI Example
http://www.w3.org/TR • There is a document available via the HTTP protocol• Residing on the machines hosting www.w3.org• Accessible via the path "/TR"
ProtocolsDescribe how messages are encoded and exchangedDifferent Layering Architectures• ISO OSI 7-Layer Architecture• TCP/IP 4-Layer Architecture
ISO OSI Layering Architecture
ISO’s Design Principles
• A layer should be created where a different level of abstraction is needed
• Each layer should perform a well-defined function• The layer boundaries should be chosen to minimize
information flow across the interfaces• The number of layers should be large enough that
distinct functions need not be thrown together in the same layer, and small enough that the architecture does not become unwieldy
TCP/IP Layering Architecture
TCP/IP Layering Architecture
• A simplified model, provides the end-to-end reliable connection
• The network layer – Hosts drop packages into this layer, layer routes
towards destination – Only promise “Try my best”
• The transport layer– Reliable byte-oriented stream
HTTP Basics• Protocol for client/server communication– The heart of the Web– Very simple request/response protocol– Relies on URI naming mechanism
• Three versions have been used– 09/1.0 – very close to Berners-Lee’s original – 1.1 – developed to enhance performance, caching,
compression– 1.0 dominates today but 1.1 is catching up
GET Method in HTTP
HTTP Response Codes
• 1xx – Informational – request received, processing• 2xx – Success – action received, understood, accepted• 3xx – Redirection – further action necessary• 4xx – Client Error – bad syntax or cannot be fulfilled• 5xx – Server Error – server failed
Domain Name System DNS (domain name service): mapping from domain
names to IP addressIPv4: • IPv4 was initially deployed January 1st. 1983 and is
still the most commonly used version.• 32 bit address, a string of 4 decimal numbers
separated by dot, range from 0.0.0.0 to 255.255.255.255.
IPv6: • Revision of IPv4 with 128 bit address
Top Level Domains (TLD) Top level domain names, .com, .edu, .gov and ISO 3166
country codesThere are three types of top-level domains:• Generic Domains were created for use by the
Internet public • Country code domains were created to be used by
individual country • . arpa domain Address and Routing Parameter Area
domain is designated to be used exclusively for Internet-infrastructure purposes
Registrars
• Domain names ending with .aero, .biz, .com, .coop, .info, .museum, .name, .net, .org, or .pro can be registered through many different companies (known as "registrars") that compete with one another
• InterNIC at http://internic.net• Registrars Directory:
http://www.internic.net/regist.html
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