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Survival of the Fittest Jini Services, Part I
Ensure the Quality of Web Services in the Age of Calm Computing
by Frank Sommers
First Published in JavaWorld, April 2001

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Spheres of Control

I'd like to conclude this article by revisiting an idea originally suggested in the late 1970s by two IBM researchers, Charles T. Davies and Larry Bjork. Extending their revolutionary idea might provide a unifying metaphor for the issues of dependability guarantees of Web-based object services.

In this scenario, when you request the planning of a trip from the system -- interfacing it via any user interface that the service provides, be it voice, a computer, and so forth -- the trip-planning service will locate all the component services needed to accomplish this objective, and bring them under a sphere of control. A sphere of control (SoC), thus, is a logical grouping of services on the network, which share a similar set of guarantees. This is illustrated in Figure 5.


Figure 5: Dynamic spheres of control

To quote from Davies' paper, "Data Processing Spheres of Control" (IBM Systems Journal, 1978):

The kinds of control considered, for which there are potentially many instances, are process atomicity, process commitment, controlled dependence, resource allocation, in-process recovery, post-process recovery, system recovery, intraprocess auditing, interprocess auditing, and consistency.... Spheres of control exist for other purposes ... examples are privacy control, transaction control, and version control for both data and procedures.

At the outset of a new SoC, services agree upon this common set of guarantees, and then interact inside this control regime. A sphere of control, therefore, would be a "contract," which services deployed by organizations or individuals could use when interacting with one another on the object Web. An SoC would have both quantitative and qualitative guarantees for each participant service, and for the SoC as a whole. SoCs, therefore, would become a unit of trust and execution on the object Web.

An SoC would be represented as an object, which is saved persistently, even after the lifetime of the process it facilitates. The advantages of its persistence are evident when we consider either auditing or reversing a process. In the latter case, suppose your trip planning was done via an SoC, and you needed to cancel your trip. Since your process used many services, you'd need to instruct each one to reverse its original action. Why not delegate this job to your SoC object representing the trip reservation? Since it has the information of what steps were taken, which services were used, and what agreements were made between each service, it could arrange a reverse action with each service.

All your SoC objects would be available on the Web (for your own use only), and you could perform auditing and action reversal from virtually anywhere. With this in place, you could ask your car to find the restaurant you liked so much a few months before: your car would provide an interface, possibly via voice, to a space where all your SoC objects are accessible. A service could find the SoC objects that have restaurant services as participants, some of which you might have marked at the time as being excellent (using your PDA). It could then read a few attributes, such as the restaurant's name, from these back to you via the car's speaker system. You could then instruct your car to make a reservation at the desired restaurant, which it will do by creating a new SoC with the object representing the restaurant on the network. This is calm computing in action.

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