The Internet
The Internet
The internet is a public global area network which is used to
transport data between computers, each of which is called a
host, connected to the internet.
transport data between computers, each of which is called a
host, connected to the internet.
The internet is used for different applications, including:
- File transfer (FTP)
- Messaging
- The World Wide Web
The terms "Internet" and "World Wide Web" are not
synonymous, although they are often loosely used as though
they were.
synonymous, although they are often loosely used as though
they were.
The World Wide Web
The world wide web is an application of the internet
which uses clients (web browsers) to send requests to
servers (web servers), and which then typically format
files which are received from the web server as graphical
page to be displayed on the client computer.
which uses clients (web browsers) to send requests to
servers (web servers), and which then typically format
files which are received from the web server as graphical
page to be displayed on the client computer.
Client Side Dynamic Web Pages
JavaScript is a programming language (originally called
LiveScript, and not derived from Java) which can be
embedded in the text of a web page. The JavaScript is
interpreted by an interpreter on the client computer, and the output of the JavaScript program is incorporated into the
displayed page.
LiveScript, and not derived from Java) which can be
embedded in the text of a web page. The JavaScript is
interpreted by an interpreter on the client computer, and the output of the JavaScript program is incorporated into the
displayed page.
Java is a programming language which can be embedded by
reference in a web page. The Java is then loaded as a
separate file from the web server, and is executed by a
Java Virtual Machine (JVM on the client computer, and
the output of the Java program is incorporated into the displayed page.
reference in a web page. The Java is then loaded as a
separate file from the web server, and is executed by a
Java Virtual Machine (JVM on the client computer, and
the output of the Java program is incorporated into the displayed page.
Server Side Dynamic Web Pages
PHP is also a programming language which can be embedded
in the text of a web page, but the code is executed on the
server, not on the client machine. The output of the php
program is sent to the client browser as a web page, with the
program replaced by its output.
in the text of a web page, but the code is executed on the
server, not on the client machine. The output of the php
program is sent to the client browser as a web page, with the
program replaced by its output.
A PHP script can access a database, and incorporate the
data into a web page. The database can be on a separate
server, accessed through a local area network. The PHP
script sends SQL statements to the database engine
program, which retrieves the data from the database,
and sends it back to the PHP script.
data into a web page. The database can be on a separate
server, accessed through a local area network. The PHP
script sends SQL statements to the database engine
program, which retrieves the data from the database,
and sends it back to the PHP script.
General Remarks
These cases are representative, not all inclusive.
JavaScript programs can be included in a web page by
reference, and retrieved from the server as a separate file.
CGI programs, usually written in Perl, also execute on
the server. The techniques can be combined; a web page
processed by a PHP script can also incorporate Java applets
and JavaScript code.
JavaScript programs can be included in a web page by
reference, and retrieved from the server as a separate file.
CGI programs, usually written in Perl, also execute on
the server. The techniques can be combined; a web page
processed by a PHP script can also incorporate Java applets
and JavaScript code.
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