HTML

The Hypertext Markup Language is not a programming language. It is, as the name already says, a language to provide a text with formatting, to define how it looks like. With tags a text is for example marked as headline. A HTML document consists generally of a header, that contains some meta data, and a body, that contains the displayed text. A special type of HTML is XHTML, which is XML compliant HTML.

All pages in the World Wide Web contain mostly HTML. Nowadays a great problem is to define a web page that it looks nearly the same in all popular browsers (Internet Explorer, Firefox, Opera, Netscape, Chrome, Konqueror, Safari and more) and their different versions.

XML

The Extensible Markup Language is used for representation and storage of hierarchical structured data. It is distinguished because it is readable for computers and also for humans. A XML document consists essentially of elements (with a start and end tag, like <tag></tag>) and attributes (<tag attribute="value">content</tag>).

The XML specification only has a few, but clear rules how such an document could look like. The central rules are:

• Each XML document has exactly one root element
• Each element has a start and an end tag
• Each attribute in an element has an unique name

Because of this XML could be easily used to store and transfer different kinds of data. Additionally nearly every state-of-the-art programming language has easy mechanisms to parse XML documents.

CSS

Cascading Style Sheets (CSS) is a declarative language for stylesheets, which is commonly used in the web. In the CSS files the look and feel of a web page and the contained HTML elements is defined. With this the design and layout of a web page are separated. This increases the flexibility and eases the maintenance of an application.

Unfortunately the CSS declarations are interpreted differently by the common browsers (like Internet Explorer, Firefox, Opera). This could lead to discrepancies in the presentation of the contents. Therefor the open source framework YAML (Dirk Jesse) helps to have a consistent presentation of a web page or a web application in different browsers.

YAML

YAML could be described by the following words:

"Yet Another Multicolumn Layout" (YAML) is an (X)HTML/CSS framework for creating modern and flexible floated layouts. The structure is extremely versatile in its programming and absolutely accessible for end users.

YAML is not an out of the box layout. A lot of additions need to be defined to get a typical design of a web page. These changes are made in defined CSS files, to make an easy upgrade to newer versions of YAML possible.

JavaScript

JavaScript has, besides the name, nothing to do with the programming language Java. While Java is used for desktop or server side web applications, JavaScript is a scripting language which is executed on the client side in the web browser.

JavaScript essentially is used to make webpages more dynamic for end users. This fits perfectly to the static defined HTML code. Nowadays JavaScript is used more and more to provide a web page the look and feel of a desktop application. The keyword in this area is AJAX.

AJAX

AJAX originally stood for Asynchronous JavaScript and XML. It is used to let appear websites more dynamically to convey the look and feel of a desktop application. This includes that the usage of a website not only consists of a client request and a server reply. Needed Information is reloaded as necessary and without disturbance of the user's interaction with the website, as it would occur while an reloading of the whole site.

The additional required data is fetched through an further request which is unnoticed from the user, an integrated in the website. AJAX became it's name originally because this happened asynchronous (in background) and per exchange of XML. Meanwhile this can happen also synchronous and per other formats. AJAX improves the possibilties of web applications and therefore was an integral part (but not exclusive part, like often communicated) of the wave that is known under the name web 2.0.