Stateful means the computer or program keeps track of the state of interaction, usually by setting values in a storage field designated for that purpose. Stateless means there is no record of previous interactions and each interaction request has to be handled based entirely on information that comes with it.
One year ago I penned Event Processing in Twitter Space, and today parts of the net are buzzing about Twitter.
In a nutshell, Twitter is a one-to-many communications service that uses short messages (140 chars or less). Following on the heels of the blogging phenomena, Twitter has been primarily used for microblogging and group communications.
Twitter, and Twitter-like technologies, has great promise in many areas. For example, you could be subscribed to the @tsunamiwarning channel on your dream island vacation and get instant updates on potential disasters. A team of people working in network management could subscribe to the @myserverstatus channel and receive updates on their health of their company IT services. Passengers could subscribe to the @ourgatestatus channel and follow up-to-date information on their fight.
Twitter was created to answer the simple question, “What are you doing now?”
It is from this operational asymmetry that complexity in event processing is required. In other words, as distributed networks grow in complexity, it is difficult to determine causal dependence when trying to diagnosis a distributed networked system. Most who work in a large distributed network ecosystem (cyberspace) understand this. The CEP notion of “the event cloud” was an attempt to express this complexity and uncertainly (in cyberspace).
The one, really big, difference between Complex Event Processing and traditional BRMS tools is that the former is loosely associated with EDA and decisions that are based on multiple events, whereas the latter is more associated with conventional request-reply SOA and automating decisions made in managed business processes.
Rule-processing is just a style of computation. Of course it is used in BRMS, but it is also used in CEP. CEP systems typically employ rules-based processing to infer higher-order events by matching patterns across many event streams within the event ‘cloud’. BRMS’s use rule processing to match patterns within data tuples representing business-orientated data. CEP systems may support the use of advanced analytics to manage predictive analysis, reasoning under uncertainty and other requirements in relation to the event cloud. Some of the better BRMS’s offer similar analytics in regard to processing business data.
Some definitions key on the question of the probability of encountering a given condition of a system once characteristics of the system are specified. Warren Weaver has posited that the complexity of a particular system is the degree of difficulty in predicting the properties of the system if the properties of the system’s parts are given. In Weaver’s view, complexity comes in two forms: disorganized complexity, and organized complexity. [2] Weaver’s paper has influenced contemporary thinking about complexity. [3]
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J. Schiefer, S. Rozsnyai, C. Rauscher, and G. Saurer. DEBS '07: Proceedings of the 2007 inaugural international conference on Distributed event-based systems, page 198--205. New York, NY, USA, ACM, (2007)