Utility Function Curve in Java Generating pdf417 in Java Utility Function Curve

Utility Function Curve using applet togenerate pdf417 on asp.net web,windows application QR Code Safty What happens pdf417 2d barcode for Java when the real-time system is late It misses its deadline then what The answer to that question determines where the system falls on the continuum from hard real time through soft real time to not real time.. Hard real-tim e systems cannot tolerate late results. Something unrecoverable happens: a person dies, a wing falls off the airplane, a million barrels of hot petroleum squirt onto the tundra, or something else unspeakable occurs. Hard real-time systems are difficult to code but simple to specify.

You have to establish that they will meet all their deadlines, but you do not have to decide what to do when the systems miss a deadline. It is like the question, "In the computer that sits in a bomb and tells it when to explode, what instruction do you put after the one that explodes the bomb " There are two questions when a system misses a deadline: 1. Should we bother to produce the result even though it will be late 2.

Should we execute a recovery routine If the result of the computation is worthless after the deadline, it makes no sense to waste computer time on it. Since the system might have missed the deadline because it was overloaded, wasting time could cause the system to miss other deadlines and convert the failure to meet a single deadline into a total shutdown. A missed deadline might require a response.

Failing to shut off the valve that fills a water tank on time could call for another valve to let some water out of the tank. Not responding to a database query on time could put up a "please wait" message on the user"s screen. A mistake in milling a part could call a human supervisor or kick the part into a scrap bin.

Utility is the economists" term for how valuable something is. Economists like to draw graphs, for example, the utility of a commodity as a function of how much you have of it. A graph (Figure 1-2) showing the utility of completion around the deadline characterizes some classes of real-time systems.

Figure 1-2. Punctuality utility functions. The first gra awt PDF-417 2d barcode ph in Figure 1-2 shows a utility function that would represent a non-real-time system. The value of completion declines slowly after the deadline, but there is barely a difference between completing on deadline and being seriously late. Think of mowing the lawn.

Getting it done earlier is better, but there isn"t any point at which it suddenly becomes urgent. The second graph shows a utility function for a soft real-time system. The value of completion has an inflection point at the deadline.

Late completion is worse than on-time completion, but the value stays positive for a while after the deadline. Think of fixing lunch for your children on a relaxed summer day. The children know the time they should be fed, and if you are late, they get fussy.

The level of hungry complaints gradually increases after the deadline, but nothing really bad will happen. On time is best, and the value of the computation drops significantly when the deadline is missed. The third graph represents a real-time problem with a serious time constraint.

After the deadline the value of completion quickly goes negative, but it does not become catastrophic. In this case, the slope of the curve decreases because the system can take remedial action. Think of a child flushing a T-shirt down the toilet.

The deadline for action is the moment before the child flushes. You would much rather stop him before he flushes. If you are late, you might be able to reach in and snag the shirt; that is unappealing, but not disastrous.

Still later there is a good chance you can recover the shirt with a plumber"s snake, but we are deep in negative utility. Still, nothing terrible has happened. The last graph represents classic hard real time.

A tiny interval after the deadline, the utility of completion goes to negative infinity. There probably is a utility value for a late result, but it is so negative that the creators of the system requirements don"t want the engineer to consider the option of occasionally missing. the deadline. Sticking with the children analogy, this is grabbing the child before she runs into traffic. Late is not an acceptable alternative.

Note The utility function graphs in Figure 1-2 show various behaviors before the deadline. The utility of early results is a whole different question. The functions show that early is the same as on time, early is a little worse than on time, and early is much worse than on time.

Since it is easy to delay the effect of an early computation, worrying about early results is generally not interesting..
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