The distribution view deals with how objects find and collaborate with each other even though they may be in different
address spaces. The distribution view includes policies for how the objects communicate, including the selection
and use of communication protocols.
In asymmetric distribution architectures, an object is dedicated to a particular address space at design
time. This makes finding that object simple during runtime because the other objects can be granted a prior
knowledge about how to locate and contact the object in question.
In symmetric distribution architectures, the location of an object isn't decided until runtime.
Symmetric architectures are useful for a complex system that must dynamically balance processing load over multiple
processors. When objects become ready to run, the distributed OS runs the object in an optimal locale, based on
the current loadings on the various processors. This improves overall performance, but at a cost--increased
complexity.
Selecting a distribution architecture is highly driven by the QoS of the collaboration. The most relevant QoS to drive the distribution
architecture include:
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Performance
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Worst case
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Average case
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Predictability
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Throughput
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Reliability
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Of message delivery
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Of message integrity
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Recurring (e.g., hardware) cost
The most important QoS requirements depend on the specific system that is being built. For example, in real-time
and embedded systems, performance can be crucial to success. In hard real-time and safety-critical systems,
worst-case delivery time is the most important.
You can represent the system by using class or structure diagrams. These diagrams show structural elements and
their relations. You can use sequence diagrams that show how these elements interact or state machines that
depict the behavioral specifications of individual elements.
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