What is markup? 

A markup language allows regular text like this, to be marked with special symbols (called tags) that tell a program, like this web-browser, how to display the text.

HTML is probably the best-known markup language. All web pages use tags that begin with a "<" and end with a ">". For example part of an HTML file might look like.

<I><B>Hi there</B></I>

When you see it in your web browser it looks like: Hi there

Some tags change the way text looks, others change the way it behaves. A hyperlink is an example of changing behavior.

What is UIML? 

UIML stands for "User Interface Markup Language."  UIML is an XML language for defining user interfaces.

Most XML languages are used for defining documents. In other words, they allow programs to break up alot of words, pictures and other data into useful chunks that can be processed by a program.

UIML, on the other hand is used for defining the actual interface elements. This means the buttons, menus, lists and other controls that allow a program to function in a graphical interface like Windows or Motif.

UIML is used to define the location, and design of controls. It also defines actions to take when certain events take place.

Users create events when they interact with the interface by typing a key on the keyboard or moving and clicking the mouse.

What is XML? 

XML stands for "Extensible Markup Language."  It's a standard way to define new, special-purpose languages.

To understand it, think of an HTML file on your computer.  That file contains a textual description of a document or Web page.  The description contains markup:  things that look like <p> and <title>, to mark things like the start of a paragraph or title.  These things in angle brackets are called tags. 

But suppose you want to describe something other than a document or a Web page?  Do you define a new language?  If you did that, the world might one day have millions of languages, creating a tower of Babel. 

Instead, the idea behind XML is to use the same rules to create new languages. Each new markup language has tags that are customized for the specific purpose at hand.  In our case, we use a customized set of tags for describing user interfaces, in a language called the UIML (User Interface Markup Language).  Because one can define their own tags, the language is "extensible". 

XML is on its way to becoming an open standard.  It is currently a W3C recommendation. 

For more information on XML, visit "Frequently Asked Questions about the Extensible Markup Language" or the W3C XML site.

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