Chapter Two
from many independent research fields (such as, discrete event simulation, active databases, network management, or temporal reasoning), and in different application fields (as business activity monitoring, market data analysis, sensor networks, etc.). Only in recent years has the term Complex Event Processing, CEP, emerged as a discipline of its own and as an important trend in industry applications where it is necessary to detect situations (specified as complex events) that result from a number of correlated (simple) events. CEP concept will be described in depth hereafter. More specifically, as represented in Figure 18, considering that sensor data is generally delivered as a stream, a sub-form of CEP known as Event Stream Processing (ESP) 66 can be used for searching different patterns in continuous streams of sensor data events.
Figure 18 Complex Event Processing (CPE) and Event Stream Processing (ESP) In the near future, some of the main challenges to be solved in the context of Virtual Sensors are: Seamless integration and interoperability of “real” and “virtual” sensors. This means that virtual sensors should be indistinguishable from real ones for the external or high level applications, but also for other sensors or system modules if necessary. This way, virtual sensors could be fed as input sensors for new virtual ones, making the flexibility and power of this approach almost unlimited. Support of (input) sensors and measurements heterogeneity. A virtual sensor should, ideally, be capable of handling input sensors of a very different nature. This results in a very powerful mechanism for implementing complex logics, also linking with CEP concepts. The integration of sensors capturing different phenomena may help 79