The advantage of executable content is one that all programmers know: the power of computers comes from the fact that they can be programmed. The growth of the use of computers has come from our ability to simply extend their capabilities whenever we have needed to. Up until very recently, when it has come to web-based information systems, all we have been able to change is the information servers. The browser has been a fixed quantity, forcing us to feed it data in a fixed format.
With the advent of executable content, we are in a situation where we can simply decide how we want to implement a connection between the user and the information we wish to provide. We can then program both the server and the browser to provide us with the desired behaviour. If, for instance, it turns out better to provide a specialized, constantly available server for a certain type of information (maybe a constantly updated database), then static web technology gives us a major headache: web servers receive requests, upon which they start up programs. If one wishes to use them to connect to a more sophisticated server, one has to get the web server to open up a connection to the more sophisticated server, relay data between it and the user, and generally oversee and convert all the communication between the database and the user. This is slow, and highly inefficient. With executable content, however, the initial web-page can contain the software to talk directly to the server, cutting out the inefficient middle-man from the communication. The user to information link now becomes a dynamic quantity.
An even better property of executable content is that the computing involved in the information exchange becomes distributed: the server's job is now to simply provide information, whereas the browser's job can include sophisticated presentation of that information, without using up the server CPU. This is very important, when one takes into account how much unused computing power is available on the modern scientist's desk. The browser has become programmable. The difference in web capability is the difference between having a television on your desk versus having a fully functional computer on your desk.
The approach described here represents a radical change in the way that we handle information on the internet, described by some as being as radical a change as the URL system that allowed the creation of the web. The URL and HTML systems gave us a simple mechanism for referring to information and then specifying what local programs could be run to use that information. Executable content, and the object-oriented approach to network services and information, allows us place any resource onto the network, as long as we can write a Java-based tool that can use that resource.