With the ubiquity of sensor networks and smart devices continuously collecting more and more data, we face the challenge to analyze an ever growing stream of data in near real-time. Being able to react quickly to changing trends or to deliver up to date business intelligence can be a decisive factor for a company’s success or failure. A key problem in real time processing is the detection of event patterns in data streams.

          Complex event processing (CEP) addresses exactly this problem of matching continuously incoming events against a pattern. The result of a matching are usually complex events which are derived from the input events. In contrast to traditional DBMSs where a query is executed on stored data, CEP executes data on a stored query. All data which is not relevant for the query can be immediately discarded. The advantages of this approach are obvious, given that CEP queries are applied on a potentially infinite stream of data. Furthermore, inputs are processed immediately. Once the system has seen all events for a matching sequence, results are emitted straight away. This aspect effectively leads to CEP’s real time analytics capability.

          Consequently, CEP’s processing paradigm drew significant interest and found application in a wide variety of use cases. Most notably, CEP is used nowadays for financial applications such as stock market trend and credit card fraud detection. Moreover, it is used in RFID-based tracking and monitoring, for example, to detect thefts in a warehouse where items are not properly checked out. CEP can also be used to detect network intrusion by specifying patterns of suspicious user behaviour.



Monitoring and alert generation for data centers:

Assume we have a data center with a number of racks. For each rack the power consumption and the temperature are monitored. Whenever such a measurement takes place, a new power or temperature event is generated, respectively. Based on this monitoring event stream, we want to detect racks that are about to overheat, and dynamically adapt their workload and cooling.

For this scenario we use a two staged approach. First, we monitor the temperature events. Whenever we see two consecutive events whose temperature exceeds a threshold value, we generate a temperature warning with the current average temperature. A temperature warning does not necessarily indicate that a rack is about to overheat. But whenever we see two consecutive warnings with increasing temperatures, then we want to issue an alert for this rack. This alert can then lead to countermeasures to cool the rack.

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