Online Programz

Internet Address :

Devices connected to the internet are called nodes. Nodes that are computers are called hosts. Each node or hosts is identified by at least one unique 32 bit numbers called Internet address.

Internet address is written as four unsigned bytes, each ranging from 0 to 255. Bytes are separated by periods.

DNS :

DNS stands for Domain Name system which associates host names that human can remember easily.

Example :

152.2.21.1 is associated with domain name such as oit unc.edu.

Inet Address Class:

Inet Address class is an encapsulation of IP address. It can be used by other classes like socket, server socket, URL, Datagram Socket, Datagram Packet and more.

Function:

Inet Address can be specified as two fields

Host name – String _ contains names of the host.

Address- integer- contains 32 bit IP address.

The method of this class can’t be called directly

Stream:

A stream is a an abstraction that either produces or consumes information. A stream is linked to a physical device by the java I/O stream.

Types Of Stream:

• Byte Stream
• Character Stream

Byte Stream :

• Handles input and output of bytes.
• Classes: Input Stream and Output Stream (important classes)
• Methods: read(), write() (important methods)

Character Stream:

• Handles input and output of characters
• Classes: Reader and Writer (important classes)
• Methods: read() and write() (important methods)

There are some characteristics that distinguish SGML from other markup languages. They are

• Descriptive Markup : The tags are descriptive such that they will be understood as soon as they are seen by anyone.

Example To mark up a letter the tag can be given the name <letter>

To mark up a paragraph the tag can be given the name<paragraph>

The information about this tags is collected outside the document in separate programs.

• Type of  Document: SGML introduces the notion of a document type defination.
• Document Type Definition describes a model of the structure of the content of SGML Document. Each SGML document has its own DTD..

The document type Declration looks like <! DOCTYPE DTD.name[internal.subset] >

SGML stands for stands for standard generalized markup language. SGML is a meta language in which one can define markup language for documents.

Markup:

Markup language means a set of conventions used together for encoding texts. It must specify what effect is allowed, what is required and how style or effect is to be distinguished for text.

Need for SGML :

SGML was orginally designed to enable the sharing of machine readble documents in large products in Government legal and aerspace industry.

It is primarly used for text and database publishing.

Example :

Oxford English dictionary which was marked up completely in SGML.

SGML has no predefined tags of its own user can create tags of their own.

PERL stands for practical extension and Report language. It is one if the most widely usednlanguages for web programming today. PERL is commonly used because of its power, its flexiility and availability of preexisting scripts. It has powerful, text processing capabilitiesn and is arguably the most popular CGI scripting language.

Example program to print a line of text.

#!c:\.perl\bin\per1

#A first program in perl

print(”welcome to perl! \n”);

Thus program output is welcome to perl!

Here in the program #-> comment charactert to instruct the interpreter to ignore everything on the current line following #.

The file can be saved with extension .PL in the directory cgi.bin.

CGI stands for common gateway interface. CGI is a set of standards by which web servers can communicate with external program to handle the data from the form. This is due to reason that web server is not programmed to process the form data.

CGI doesn’t communicate directly with browser. The browser talks with server, server in turn talk with CGI program and CGI returns the answer to server and server talks to the browser.

Working Of CGI :

A CGI is only a program which are generally called scripts because they were written in UNIX and shell script and PERL. PERL is a interpreted and immediately compiled into machine instructions.C language is also used, but it is not called as script normally.After looking at CGI program, server access information from browser.Before launching the scripts, it prepares a number of variables called environment variables representing the current state of server. If server is busy with various scripts, CGI excutes its scripts at once each with its own environment.

TCP stands for transmission control protocol. It provides a means for the users to exchange data as streams of octets and these streams are transmitted in segments each in turn consists of TCP header and a portion of the users data.

• Data are passed to TCP by a user in a sequence of TCP send primitives
• The data are buffered in send buffer.
• TCP assembles the data from the send buffer in a segment and transmits the segment.
• The segment received by the TCP entity will be stripped off its header and the data is placed in the receive buffer.
• The user will be notified by the TCP deliver primitive that data are available for delivery.