DIVA is designed as a distributed object oriented system. The DIVA components are written in C++ and Java, and can run on different platforms. We use the Common Object Request Broker Architecture (CORBA) to let our distributed objects communicate with each other. CORBA (Orfali & Harkey, 1997; Siegel, 1996) abstracts from hardware, operating systems and programming languages. By using the interface definition language (IDL) to describe the interfaces between components and by making use of the object request broker (ORB), distributed components are able to communicate.
Voyager (ObjectSpace, 1997) is an agent ORB written purely in Java, which supports CORBA. Voyager allows us to use mobile objects, a feature which CORBA does not have. We use Voyager to construct the mobile controller components. These components are able to "dock" at a user environment and can subsequently show their user interface on the screen to let the user interact with it.
We use VRML (ISO, 1997) as the main visualization tool. The users are able to navigate through the VRML worlds by using a VRML-browser. The External Authoring Interface (EAI) makes it possible to control the VRML worlds dynamically via the Java and Javascript languages.
The visualization gadgets in the presentation component are represented by mobile display agents. These agents are constructed using Voyager. Display agents can also "dock" in a user environment and, in addition, get access to the local VRML world. They collect the needed information from shared concept spaces to build and maintain the 3D visualization.
The combination of CORBA and the Web enables access to information resources by means of HTML, Java and VRML (see also Rohrer & Swing, 1997). For example, the simulation and shared concept space can be hosted on a Unix server while the presentation components are executed in a Web-browser on Windows client machines.