Introduction to Web

Introduction To Web
The term “web” means the internet service for navigating through Web pages. The protocol used for this type of communication is the HTTP (Hyper Text Transfer Protocol), which explains the fact that you’re entering URLs that begin with http://.

The HTTP protocol is currently at version 1.1 (specified by the W3C). Now the HTTPS (Secure HTTP) is increasingly used with the use of electronic commerce systems because it is a secure protocol for costing requests exchanged between the browser and the server.

Today, WAP (Wireless Application Protocol) allows a WAP-compatible mobile phone to communicate with the WAP gateway to the mobile operator. The papers will then be converted according to the HTTP protocol by the bridge. The latest version of WAP specified by the WAP Forum (the authority to define the WAP standard) is version 1.1 (early 2001).

HTML and static pages
The standard now established for the dissemination of documents on the web is HTML (HyperText Markup Language). HTML is used to define the presentation of the document and hyperlinks to other documents using formatting tags. The W3C, the body responsible for standardizing Internet standards currently (early 2001) specified the HTML version 4.01. The DHTML (Dynamic Hypertext Markup Language) which we often hear is not a language itself. It is actually a set of additional languages to HTML and to make a web page more dynamic. These languages are:

• HTML 4.0 or higher
• JavaScript, to perform operations on the client browser.
• The DOM (Document Object Model) defining a tree of objects representing the structure of the document. This allows manipulating all objects in the document.
• The style sheets (CSS - Cascading Style Sheets), combining them in one document defining the styles of each tag of a Web page or an entire site.

The dynamic web pages
A “static page” is a web page consisting of a text files containing HTML code and possibly images and links to other documents. A site consists of static Web pages and will be called “static website. A static website is sufficient when it contains a few dozen pages, but its operations and its updating can quickly reach the following limits:

• Maintenance difficult due to the requirement to manually change each page (especially in cases where all pages have the same menu).
• Unable to return a custom page as the visitor.
• Unable to create a page dynamically as entries in a database.

That is why solutions to automate the generation of web pages on the server have been developed. There are many ways to implement a scripting language on the web server, including the most common are:

• The first historically known as CGI (Common Gateway Interface) was to interpret programs (usually written in Perl or C), then return to their content compatible with the HTTP protocol.
• The language ASP (Active Server Pages) Microsoft has simplified the writing of these scripts by manipulating objects in VBScript.
• The PHP (Hypertext Preprocessor) employs its own language (derived from C and Perl) and allows many features (equivalent to those of technology ASP).
• The language JSP (Java Server Pages) is the latest among these technologies. It allows you to use the power of Java to create dynamic web pages.

Java and Web
Java has long been mainly used to write applets, i.e. small programs running on the client browser, within a web page, thus make the page more interactive (but also much slower).
Java is now used mainly on the side of the web server for the following reasons:

• Java is portable (it can run on any platform).
• Java is safe (it was designed not to cause runtime error may create security vulnerabilities for the server).

Thus, there are different entities Java:

• Servlets, to make treatment as the user’s query (access to databases with JDBC, communication with other servlets through technology RMI, interrogation of LDAP, …).
• The JSPs representative HTML code in Java which is called.
• The EJB (Enterprise JavaBeans), components written in Java objects residing on an application server to access their methods.

XML
HTML quickly showed its limits, not only by its limited number of tags, but by the impossibility of separating content and presentation, which induces a problem of simple updates of the presentation. Thus, XML offers itself as a meta-language, i.e. a language used to define a new language (new tags). In addition, since XML separates the presentation of data, it is possible to exchange documents in XML format without influence on the shape of them. This enables consumers to make simple adaptation of content to a browser or to any display device (in this way, the WML (Wireless Markup Language) is an implementation of XML for viewing pages web on mobile handsets).
XSL (eXtensible Stylesheet Language) allows you to format a XML document using formatting rules to form a document in another format (HTML, WML, PDF, LaTeX, …)
XML organizes information using a tree structure defined by the DOM (Document Object Model), it is possible to browse an XML document with a parser (also called parser), that is to say program using a library function (API for Application Program Interface) to read and edit an XML document.