An important part of the litmus test is the application-deployment mechanism. Applications should be able to run without needing client software or plug-ins to be installed prior to connection. This dynamic deployment mechanism enables all or part of the application to be downloaded to the client machine and run locally, allowing the application to benefit from local machine services such as the display, input devices, and local interactive controls in the user interface. Application performance and interactivity are made possible because code is downloaded and run on the local machine.
What parts of the application really need to be downloaded and run? Certainly not the application logic. Application logic interacts with data not on the client machine (for example, corporate databases, data repositories, and shared information services). In addition, the application logic I’m talking about consists of C++ objects running on the server.
The part of the application that gets downloaded and run on the client machine is the presentation layer. But how do you get the presentation onto the client machine? This presentation layer includes the GUI elements along with just enough application logic to convert user interface events into object state changes. These state changes, and only these state changes, are what your client will send across the Internet to the server.
One way to do this is by using what I call “Just Enough Java.” This use of Java is simply pragmatic. Besides providing a dynamic download of the presentation layer, Java offers platform independence, effectively making your Visual C++ applications cross-platform. In addition, as a client-side solution, Java takes advantage of its virtual-machine security model.