FEDAI , A. Shahir
This paper will present general information about
the web and discusses some of the authoring techniques. We will start with HTML and JavaScript and
then look at other technologies such as ASP and java.
The concept of the World Wide Web, or simply the
web, was born in 1983 at the CERN labs in Geneva. Tim Berners-Lee at CERN was looking for a way to disseminate
information in a platform independent manner.
The scheme he devised was placed in the public domain in 92, thus the
start of the web.
The original documents used in the web were in a new
format called HTML. HTML stands for
Hyper Text Markup Language and is the publishing language of the web. HTML is a language that consists of
predefined tags. All documents begin and end with the
<HTML>…</HTML> tags. There are other tags for images, lines,
paragraphs and so on. These tags are
included with the text and tell the browser whether the text is to be a
paragraph, a heading, an image, a table, etc.
HTML is static by nature. It is
there to present the information to the user.
While HTML creates basic, static web pages of text
and graphics only, scripting languages add the extra dimension of being able to
accept information from the user and being able to return results that depend
on the users input.
There are three major scripting languages Jscript,
VBScript and JavaScript.
JavaScript is the original scripting language for
the browser. Although the syntax is
similar to java, they are not to be confused.
Java is a complete programming language while JavaScript is not.
For example, while JavaScript can control browser
behavior and content, it is not capable of drawing graphics on the HTML
document. JavaScript is designed to
create small, efficient programs, which can do many things such as performing
repetitive tasks and handling events generated by the user.
Microsoft with Internet Explorer 3 introduced
VBScript. VBScript is based on the
syntax of Visual Basic.
The code for all the scripting languages mentioned
above can be viewed by going to the source command on the browser.
This is a set of extensions to HTML and will make
use of some of the properties of the HTML 4.0 standard. The techniques used will allow you to
position elements exactly and move them around without a page refresh.
Dynamic HTML is not a new language or new set of
tags. It is just a way to manipulate
the document. This is done by the
Document Object Model. This is a way to
represent the web page in way that it’s content is easily accessible by the
scripting language. The document object
is made up of properties, methods and events, which can be accessed directly by
the script code. This will allow the
page to become dynamic.
ASP or Active Server Pages are server side text files that are
processed by the server. ASP files
contain both scripting and HTML. Although, the scripting part of an ASP file
can be written using JavaScript, VBScript is the scripting language that is
used most often. An ASP file can be
saved with an asp extension or the code can be contained within the <%…%>
tags. In both cases the server will
translate the code.
Active Server Pages enables the server and the client to communicate via
the HTTP protocol of the World Wide Web.
When a client sends a request to the server, it is directed to the
appropriate ASP page and after it is processed it is sent back to the client. Most times this involves interacting with a
database, which is one of the reasons why ASP is used.
The two most common HTTP request types are the GET and POST
methods. A get method retrieves
information from the server. For
example, to get an image or a file. The
POST method posts information to the server.
Some common uses of post requests are to send the information from an
HTML form to the server. This
information could be used to search the Internet or to query a database and
find matches.
ASP code is very secure and cannot be viewed by anyone using the
browser’s source command. The code is
ran at the server and is inaccessible by the client’s browser.
Java is a cross platform language for developing
applications. The idea is to use java
code in the form of applets, which are essentially java components that can be
inserted into the web page by using the <applet> tag. Java enjoys better functionality then some
scripting languages in areas such as graphics and file-handling and strong
database support through JDBC (Java Database Connectivity). Java can provide these powerful features
without compromising the security of any system. The reason is that these applets will run at a so-called sandbox
and out of the system. Microsoft and
Netscape browsers both have built in java support. Java code is used with the <OBJECT> or <APPLET> tags
which tell the browser to download a java file from the server and execute the
file at the browser using the built in Java Virtual Machine. This is the reason why it takes time to
download java applets and run them.
ActiveX Controls
These are self-contained programs or
components. ActiveX controls are
usually written in Visual Basic or C++ and when added to a web page they
provide specific functionality. An
example of this might be a timer, client authentication, graphs or database
access. ActiveX controls are added to
the HTML page and used with the <OBJECT> tag. The code for the ActiveX controls is executed by the browser. Microsoft developed ActiveX controls and
although they are compatible with the HTML standard, they are not supported by
most browsers without an ActiveX plug-in.
ActiveX components on the other hand are use for server side
functionality.
CGI stands for common gateway interface and is a mechanism for creating scripts on the server, which in tern can be used to create dynamic web pages. CGI technologies have been around for a while and there are many web pages that use them in conjunction with a scripting language. CGI allows the user to invoke another program such as Perl on the server to create a dynamic web page. The CGI will pass the user’s data to the program and it will be processed to provide functionality. One of the problems with using CGI is that it must be used with a program that can manipulate text and be able to communicate with other software. Some of the languages that can do this and work on any operating system are C, C++ and Perl.
There are other technologies for developing web
pages. Some of these are ColdFusion and
Java Server Pages that work like ASP as a server side solution. But the most common ones are the
technologies mentioned above.
Here are examples of some of the techniques we
looked at in this paper.
The first one is an example of a static html
page. The second is an example of an
interactive page that uses JavaScript to take information from the user and
calculate the payments for a house. The
third is an example of a Java Applet and will not execute properly with
Internet Explorer.
1.
Java2
in 24 hours by Rogers Cadenhead, SAMS 1999
2.
Internet
and the World Wide Web How to program by Deitel, Deitel & Nieto, Prentice
Hall 2000
3.
Active
Server Pages in 24 Hours by Wille and Koller, SAMS 1999