Friday, November 20, 2009

On Inexact events

Back to chapter 11 in the EPIA book that deals with challenges that developers and users of event processing systems should be aware. One these topics is the issue of inexact events. The basic assumption about current systems is this is a projection of the "closed world assumption" kind of thinking, which assumes that every event that is reported really happened, that every details in the event payload is accurate, and that every event that happened was indeed reported. In reality, one or more of these assumptions may be invalid from several reasons, as shown in the following figure:

As shown in this figure there are several reasons for making one or more of these assumptions invalid.

The source (e.g. sensor) may malfunction; if the source is an instrumented program, there may be a bug in the instrumentation.

The source (event producer) may be malicious, and send wrong information in order to sabotage the system.

The inexactness maybe a projection of temporal anomalies discussed before, e.g. derived event that has not been detected.

This inexactness may be propagated, as a derived event is derived from an event which is by itself inexact.

The source itself may be imprecise, thus some of the content may not be accurate.

The input events may be based on sample or estimates.

The uncertainty does not stop in event content, it also exists in the bridge between events and situations, I'll write on that topic in a separate posting.

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