A Brief Overview of the VIOLA Engine, and its Applications

Viola is a tool for the development and support of visual interactive media applications. Possible viola applications range from a simple clock to a World Wide Web hypermedia browser (ViolaWWW). ViolaWWW is what most people equate with "Viola". It's a convenient association, but it is important to keep in mind that ViolaWWW (the Viola−based World Wide Web browser) is just an application, albeit the most significant, of the Viola toolkit/language system. And, that Viola can be used to build many other applications. This paper will briefly gloss over the basics of the Viola engine, then briefly describe some Viola applications. The first section is a little thick with technical material, so if you're more interested in what Viola can do, read the Applications section first. At the basic level, the Viola system is a combination of the following major subsytems: An object oriented system. A scripting language for programming the behaviour of objects. A graphical user interface toolkit. Special applications supporting libraries, such as for XPM, GIF, and WWW. The basic motivation for an object model is to control complexity: to provide a relatively simple way of data encapsualization; for improving the size scalability and reusability. The single inheritance classing model used in viola defines the basic types, or "classes", of object instances. Many of these predefined class types happen to be GUI oriented, because of the current application emphasis on hypermedia. But, many classes are non−visual and have nothing to do with GUIs. An object model is enforced to control complexity: to provide a relatively simple