unit 1 programming web vtu

8/22/2019 Unit 1 Programming WEB VTU

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Prasad B SAssistant Professor

Dept. of CSE\ISESDMIT, Ujire

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1960s- U.S Department of Defense (DoD) becameinterested in developing a new large scalecomputer network.

The DoDs Advanced Research Projects Agency(ARPA) funded the construction of the first suchnetwork established at UCLA in 1969 . Hence it wasnamed as ARPAnet.

Early use-simple text-based communicationsthrough e-mail.

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Other Networks (1970s-80s) BITNET( Because its Time network) by City University of

New York

CSNET (Computer Science Network) connected Universityof Delware, Purdue University, University of Wisconsin,RAND Corporation etc. Provided E-mail service.

NSEnet( National Science Foundation) in 1986 initially

connected five universities later connected manyorganization and establishment and connected 1millioncomputers by 1992. In 1995 it became known asInternet.

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The Internet is a global system of interconnectedcomputer networksthat use the standardInternet Protocol Suite (TCP/IP)

Since 1982, all connections use TCP/IP- TCP/IP

hides the differences among devices connectedto the Internet

It consists of millions of private, public,academic, business, and government networks oflocal to global scope that are linked by a broadarray of electronic and optical networkingtechnologies.

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All devices connected to the Internet areuniquely identified using IP address.

The Internet Protocol (IP) address of amachine connected to the Internet is a unique32-bit number.

IP addresses usually are written as four 8-bitnumbers, separated by periods.

New standard IPv6 128 bits.http://www.ip-adress.com/whois/devilsproxy.com

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http://www.ip-adress.com/whois/devilsproxy.comhttp://www.ip-adress.com/whois/devilsproxy.comhttp://www.ip-adress.com/whois/devilsproxy.comhttp://www.ip-adress.com/whois/devilsproxy.com


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Text based names to remember IP address technicallyknown as Domain Name System(DNS).

These names begin with the names of the hostmachine, followed by progressively larger enclosingcollection of machines, called domains.

There may be two, three or more domain names. DNSis of the formhostname.domainName.domainName .Example:vtu.ac.in First domain : Hostname

Second domain and so on : Domain of which firstdomain is a part Last Domain : Type of organization. Ex: .com, .gov,

.org, .in

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The DNS has to be converted to IP address beforedestination is reached because computer understands only

numbers.

The conversion is done with the help of name server.

As soon as domain name is provided, it will be sent acrossthe internet to contact name servers.

This name server is responsible for converting domain

name to IP, If one of the name servers is not able to convert

DNS to IP, it contacts other name server.

This process continues until IP address is generated. Oncethe IP address is generated, the host can be accessed.

The hostname and all domain names form what is known as

FULLY QUALIFIED DOMAIN NAME.

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In 1980s, different protocols on TCP\IP hadbeen developed to developed to support avariety of Internet uses. FTP To transfer files over Internet

Telenet- Remote login

Usenet Electronic bulletin board

mailto message over Internet

Drawback: User had to learn interfaces of all

the different protocols.

Solution: World Wide Web (WWW)

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1989: Tim Berners Lee and his group proposed a new

protocol for the Internet whose intention was to allowdocuments exchange.

The proposed new system was designed to allow auser anywhere on the Internet to search for andretrieve documents from the databases on anynumber of different document-serving computers.

The system used hypertext, which is text withembedded links to text in other documents to allownon-sequential browsing of textual material.

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Units of Web information: Pages Documents Resources

Documents are texts with embedded links toother documents, they mal also have images,sound recordings or other media. In suchcase it is called hypermedia.

These documents can be accessed by webbrowsers and are provided by web servers.

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It is important to understand that the Internetand the Web is not the same thing.

The Internet is a collection of computers and otherdevices connected by equipment that allows themto communicate with each other.

The Web is a collection of software and protocolsthat has been installed on most, if not all, of thecomputers on the Internet

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Client: Request for Information. Server: Provides service by providing

requested information.

Most application on WEB operates in thisclient\server configuration.

Client: Web Browser

Server: Web Server

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Documents provided by servers on the Web are

requested by browsers, which are programsrunning on client machines.

First browsers were text based, not capable ofdisplaying graphics, images, interface.

1993, Mosaic, first graphical interface browser,developed by NCSA ( National center for supercomputer application)

Resulted in explosive growth of web usage.


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Programs that provide documents to requestingbrowsers ( clients).

First two servers: Server at CERN in Europe Server at NCSA at university of Illinois

Commonly Used web servers: Apache Microsoft Internet Information Server (IIS)

Web browser specifies a address of a data file onserver or a program stored in the server that theclient wants executed, with the output of theprogram returned to the client.

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All the communications between a web client and a web serveruses the standard protocol HTTP

When a web server begins execution, It informs the OS under which it is running & it runs as a background

process

A web client or browser,

1. Opens a network connection to a web server,2. Sends information requests and possibly data to the server,3. Receives information from the server and4. closes the connection.

The primary task of web server is to1. Monitor a communication port on host machine,2. Accept HTTP commands through that port and3. Perform the operations specified by the commands.

When the URL is received, it is translated into either a filename ora program name.

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Common characteristics of web servers

Web servers have two main directories: 1. Document root (servable documents) 2. Server root (server system software)

The files stored directly in the document root are those availableto clients through top level URLs

The secondary areas from which documents can be served arecalled virtual document trees.

Many servers can support more than one site on a computer,potentially reducing the cost of each site and making theirmaintenance more convenient. Such secondary hosts are called

virtual hosts.

Some servers can serve documents that are in the document rootof other machines on the web; in this case they are called asproxy servers.

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Apache: Began as the NCSA server httpd Most widely used web server. Fast and Reliable Open source software and free Best available server for UNIX based systems

which is preferred for servers. Contains three configuration files:

Httpd.conf Srm.conf Access.conf

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Supplied with Microsoft windows serversystems.

Provides similar service to that of Apache.

IIS Snap-in is a window based (GUI)management program to configure the serverunlike configuration file of Apache.

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Uniform Resource Locators (URLs) are used to identify different kinds of

resources on Internet. If the web browser wants some document from web server, just giving

domain name is not sufficient because domain name can only be usedfor locating the server.

It does not have information about which document client needs.

Therefore, URL should be provided. The general format of URL is:

scheme: object-address

Example: http: www.vtu.ac.in/results.php The scheme indicates protocols being used. (http, ftp, telnet...) In case of http, the full form of the object address of a URL is as follows: http://fully-qualified-domain-name/path-to-document

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URLs can never have embedded spaces. It cannot use special characters like semicolons,

ampersands and colons The path to the document for http protocol is a sequence

of directory names and a filename, all separated bywhatever special character the OS uses. (forward orbackward slashes)

A path that includes all directories along the way is calleda complete path.

Example: http://www.vtu.ac.in/index.html

In most cases, the path to the document is relative tosome base path that is specified in the configuration filesof the server. Such paths are called partial paths.

Example: http://www.vtu.ac.in/

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A browser determines the format of adocument it receives by the help of MIME.

A web server attaches MIME formatspecification to the beginning of thedocument provided to browser.

When browser receives the document, it usesthe MIME specification to determine qwhat to

do. MIME specification have the following format:

type/subtype

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The most common types of MIME are texts,image and video.

Common text subtypes are plain and html.

Common image subtype gif and jpeg.

Common video subtype mpeg and quicktime.

Server determines the file type by usingfilenames extension.

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Name of experimental type begins with x. Ex: video/-x msvideo

Web provider can add an experimentalsubtype by having its name added to the listof MIME specification in web providersserver.

Web browser must supply a support program

called helper applications or plug-ins.

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All web communications and transactionsuses the same protocol HTTP.

Current version is HTTP1.1- stable, formallydefines as RFC 2616.

Two phases : Request Response

Each communication consists of two parts, a

header and a body. Header- Information about communication Body Data of the communication if any

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General form of an http request is as follows:1. HTTP method Domain part of the URL HTTP version

2. Header fields

3. Blank line

4. Message body Example:

GET /cs.uccp.edu/degrees.html HTTP/1.1

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Commonly used HTTP request methods

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Optional Header fields have four categories: General: For general information such as date Request: Included in the request headers Response: For response headers Entity: Used in both request and response headers.

- Common request fields: Accept: text/plain Accept: text/* If-Modified_since: date

- Common response fields: Content-length: 488 Content-type: text/html

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Host: hostname request field gives the nameof the host.

If the request has a body length of the bodymust given with a content-length field.

Header of a request must be followed by ablank line, which is used to separate theheader from the body.

GET , HEAD, DELETE methods do not havebodies.

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GET http://www.tiggerwigger.com/ HTTP/1.0

Proxy-Connection: Keep-Alive

User-Agent: Mozilla/5.0 [en] (X11; I; Linux 2.2.3 i686)

Host: www.tiggerwigger.com

Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg,

image/png, */ *

Accept-Encoding: gzip

Accept-Language: en

Accept-Charset: iso-8859-1, *, utf-8

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The general form of an HTTP response phase1. Status line

2. Response header fields

3. Blank line

4. Response body Status line

HTTP version three digit status code status code explain

HTTP/1.1 200 OK

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Common status codes: 404 not found

200- OK 500- Server encountered problem

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Several lines of information about theresponse header.

Content-type : only essential field.HTTP/1.1 200 OK

Date: Sat, 25 July 2009 20:15:11 GMTServer: Apache /2.2.3 (CentOS)

Last-modified: Tues, 18 May 2004 16:38:38 GMT

Etag: "1b48098-16a-3dab592dc9f80"

Accept-ranges: bytes

Content-length: 364

Connection: close

Content-type: text/html, charset=UTF-8

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Fertile ground for security problems. Transmit data without any interception and

corruption.

Security issues for a communication betweena browser and a server:

1. Privacy

2. Integrity

3. Authentication4. Nonrepudiation

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Encryption:Basic tool to support privacy andintegrity.

Symmetric and Asymmetric

Private-Key encryption and Public keyencryption

Public key encryption in 1976 by WhitfieldDiffie and Martin Hellman.

Most widely used public key encryption is RSAalgorithm -1977- by Ron Rivest, Adi Shamirand Leonard Adelman of MIT.

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Viruses, Zombies, worms, hacking .. Solution is to use Anti Virus software's and

keeping it up to date.

Virus examples: ILOVEYOU 2000

CodeRedvirus 2001

Blaster Worm 2003

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Most common tools used in the Webprogramming.

XHMTL, XML, Javascript, Java, Perl, PHP, Ruby,AJAX, Rails

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To describe the general form and layout of documents

An XHTML document is a mix of content and controls

Controls are tags and their attributes

Tags often delimit content and specify something about how the content should be

arranged in the document Attributes provide additional information about the content of a tag

Tools for creating XHTML documents

XHTML editors - make document creation easier, Shortcuts to typing tag names,

spell-checker,

WYSIWYG XHTML editors- Need not know XHTML to create XHTML documents

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Plug ins

Integrated into tools like word processors, effectively converting them to WYSIWYG

XHTML editors

Filters

Convert documents in other formats to XHTML

Advantages of both filters and plug-ins:

Existing documents produced with other tools can be converted to XHTML documents

Use a tool you already know to produce XHTML

Disadvantages of both filters and plug-ins:

XHTML output of both is not perfect - must be fine tuned

XHTML may be non-standard

You have two versions of the document, which are difficult to synchronize

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XML

A meta-markup language

Used to create a new markup language for a particular purpose or area

Because the tags are designed for a specific area, they can be meaningful

No presentation details

A simple and universal way of representing and transmitting data of any textual kind

JavaScript

A client-side XHTML-embedded scripting language

Only related to Java through syntax

Dynamically typed and not object-oriented

Provides a way to access elements of XHTML documents and dynamically change

them

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Flash

A system for building and displaying text, graphics, sound, interactivity,

and animation (movies)

Two parts:

Authoring environment

Player

Supports both motion and shape animation

Interactivity is supported with ActionScript

PHP

A server-side scripting language

Similar to JavaScript

Great for form processing and database access through the Web

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Ajax

Asynchronous JavaScript + XML

No new technologies or languages

Much faster for Web applications that have extensive user/server interactions

Uses asynchronous requests to the server Requests and receives small parts of documents, resulting in much faster responses

Java Web Software

Servlets server-side Java classes

JavaServer Pages(JSP) a Java-based approach to server-side scripting, an alternative

to servlets

JavaServer Faces adds an event-driven interface model on JSP

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ASP.NET

Does what JSP and JSF do, but in the .NET environment

Allows any .NET language to be used as a server-side scripting language

ASP.NET documents are compiled into classes

Ruby

A pure object-oriented interpreted scripting language

Every data value is an object, and all operations are via method calls

Most operators can be redefined by the user

Both classes and objects are dynamic

Variables are all type-less references to objects

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A development framework for Web-based

applications

Particularly useful for Web applications that

access databases

Written in Ruby and uses Ruby as its primary

user language Based on the Model-View-Controller architecture

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