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Chapter 4 of Inside the Java Virtual Machine
Network Mobility
by Bill Venners

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A New Software Paradigm

The shift away from the mainframe model towards the distributed processing model was a consequence of the personal computer revolution, which was made possible by the rapidly increasing capabilities and decreasing costs of processors. Similarly, lurking underneath the latest software paradigm shift towards distributed processing with network-mobile code is another hardware trend--the increasing capabilities and decreasing costs of network bandwidth. As bandwidth, the amount of information that can be carried by a network, increases, it becomes practical to send new kinds of information across a network; and with each new kind of information a network carries, the network takes on a new character. Thus, as bandwidth grows, simple text sent across a network can become enhanced with graphics, and the network begins to take on an appearance reminiscent of newspapers or magazines. Once bandwidth expands enough to support live streams of audio data, the network begins to act like a radio, a CD-player, or a telephone. With still more bandwidth, video becomes possible, resulting in a network that competes with TV and VCRs for the attention of couch potatoes. But there is still one other kind of bandwidth-hungry content that becomes increasingly practical as bandwidth improves: computer software. Because networks by definition interconnect processors, one processor can, given enough bandwidth, send code across a network for another processor to execute. Once networks begin to move software as well as data, the network begins to look like a computer in its own right.

As software begins to travel across networks, not only does the network begin to take on a new character, but so does the software itself. Network-mobile code makes it easier to ensure that an end-user has the necessary software to view or manipulate some data sent across the network, because the software can be sent along with the data. In the old model, software executables from a local disk were invoked to view data that came across the network, thus the software application was usually a distinct entity, easily discernible from the data. In the new model, because software and data are both sent across the network, the distinction between software and data is not as stark--software and data blur together to become "content."

As the nature of software evolves, the end-user's relationship to software evolves as well. Prior to network-mobility, an end-user had to think in terms of software applications and version numbers. Software was generally distributed on media such as tapes, floppy disks, or CD-ROMs. To use an application, an end- user had to get the installation media, physically insert them into a drive or reader attached to the computer, and run an installation program that copied files from the installation media to the computer's hard disk. Moreover, the end-user often did this process multiple times for each application, because software applications were routinely replaced by new versions that fixed old bugs and added new features (and usually added new bugs too). When a new version was released, end-users had to decide whether or not to upgrade. If an end-user decided to upgrade, the installation process had to repeated. Thus, end-users had to think in terms of software applications and version numbers, and take deliberate action to keep their software applications up-to-date.

In the new model, end-users think less in terms of software applications with discrete versions, and more in terms of self-evolving "content services." Whereas installing a traditional software application or an upgrade was a deliberate act on the part of the end-user, network-mobility of software enables installation and upgrading that is more automatic. Network-delivered software need not have discrete version numbers that are known to the end-user. The end-user need not decide whether to upgrade, and need not take any special action to upgrade. Network-delivered software can just evolve of its own accord. Instead of buying discrete versions of a software application, end-users can subscribe to a content service--software that is delivered across a network along with relevant data--and watch as both the software and data evolve automatically over time.

Once you move away from delivering software in discrete versions towards delivering software as self- evolving streams of interactive content, your end-user loses some control. In the old model, if a new version appeared that had serious bugs, an end-user could simply opt not to upgrade. But in the new model, an end- user can't necessarily wait until the bugs are worked out of a new version before upgrading to the new version, because the end-user may have no control over the upgrading process.

For certain kinds of products, especially those that are large and full-featured, end-users may prefer to retain control over whether and when to upgrade. Consequently, in some situations software vendors may publish discrete versions of a content service over the network. At the very least, a vendor can publish two branches of a service: a beta branch and a released branch. End-users that want to stay on the bleeding edge can subscribe to the beta service, and the rest can subscribe to the released service that, although it may not have all the newest features, is likely more robust.

Yet for many content services, especially simple ones, most end-users won't want to have to worry about versions, because worrying about versions makes software harder to use. The end-user has to have knowledge about the differences between versions, make decisions about when and if to upgrade, and take deliberate action to cause an upgrade. Content services that are not chopped up into discrete versions are easier to use, because they evolve automatically. Such a content service, because the end-user doesn't have to maintain it but can just simply use it, takes on the feel of a "software appliance."

Many self-evolving content services will share two fundamental characteristics with common household appliances: a focused functionality and a simple user-interface. Consider the toaster. A toaster's functionality is focused exclusively on the job of preparing toast, and it has a simple user-interface. When you walk up to a toaster, you don't expect to have to read a manual. You expect to put the bread in at the top and push down a handle until it clicks. You expect to be able to peer in and see orange wires glowing, and after a moment, to hear that satisfying pop and see your bread transformed into toast. If the result is too light or too dark, you expect to be able to slide a knob to indicate to the toaster that the next time, you want your toast a bit darker or lighter. That's the extent of the functionality and user-interface of a toaster. Likewise, the functionality of many content services will be as focused and the user-interface will be as simple. If you want to order a movie through the network, for example, you don't want to worry whether you have the correct version of movie-ordering software. You don't want to have to install it. You just want to switch on the movie-ordering content service, and through a simple user-interface, order your movie. Then you can sit back and enjoy your network-delivered movie as you eat your toast.

A good example of a content service is a World Wide Web page. If you look at an HTML file, it looks like a source file for some kind of program. But if you see the browser as the program, the HTML file looks more like data. Thus, the distinction between code and data is blurred. Also, people who browse the World Wide Web expect web pages to evolve over time, without any deliberate action on their part. They don't expect to see discrete version numbers for web pages. They don't expect to have to do anything to upgrade to the latest version of a page besides simply revisiting the page in their browser.

In the coming years, many of today's media may to some extent be assimilated by the network and transformed into content services. (As with the Borg from Star Trek, resistance is futile.) Broadcast radio, broadcast and cable TV, telephones, answering machines, faxes, video rental stores, newspapers, magazines, books, computer software--all of these will be affected by the proliferation of networks. But just as TV didn't supplant radio entirely, network-delivered content services will not entirely supplant existing media. Instead, content services will likely take over some aspects of existing media, leaving the existing media to adjust accordingly, and create some new forms that didn't previously exist.

In the computer software domain, the content service model will not completely replace the old models either. Instead, it will likely take over certain aspects of the old models that fit better in the new model, add new forms that didn't exist before, and leave the old models to adjust their focus slightly in light of the newcomer.

This book is an example of how the network can affect existing media. The book was not entirely replaced by a content service counterpart, but instead of including resource pointers (sources where you can find further information on topics presented in the book) as part of the book, they were placed on a web page. Because resource pointers change so often, it made sense to let the network assimilate that part of the book. Thus, the resource pointers portion of the book has become a content service.

The crux of the new software paradigm, therefore, is that software begins to act more like appliances. End-users no longer have to worry about installation, version numbers, or upgrading. As code is sent along with data across the network, software delivery and updating become automatic. In this way, simply by making code mobile, Java unleashes a whole new way to think about software development, delivery, and use.

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