FEDAI , A. Shahir
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.
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.
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.
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.
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