Abstract
Reactivity, the ability to detect events and react to them accordingly by executing appropriate actions, has long been studied in the field of Active Databases and more recently, in the context of theWorld Wide Web. A common approach for implementing reactive behaviour and evolution in the Web is the use of reactive languages. Such languages use reactive rules for describing the reactive behaviour of a system and in particular, Event-Condition-Action (ECA) rules. The declarative semantics of such rules specifies that upon event detection, if the system’s state satisfies the stated conditions then a group of actions are executed. One of the key aspects in the implementation of reactivity is thus the development of event detectors. These systems are responsible for registering event expressions, detecting the events specified by registered expressions and then notifying the interested systems about the occurrence of events. Events can be broadly classified into atomic and composite events. An atomic event is something that happens atomically (it occurs completely or not at all) at a given point in time. On the other hand, composite events are combinations of other events (atomic or composite). They represent situations that occur when their constituent events occur and they are expressed by expressions of an event algebra. In this work, we present the implementation of a complex event detector for the Web. It detects composite events specified by expressions of an illustrative sublanguage of the event algebra SNOOP. This notification system was implemented as a component of the General Framework for Reactivity and Evolution in theWeb [7], proposed by the Evolution and Reactivity Working Group of the REWERSE 1 project. In addition, we present a comparative analysis of some active languages and more specifically, of the event detectors used by them. The aim of this analysis was to compare different approaches for implementing such systems.

URL:
http://rewerse.net/publications/rewerse-publications.html#REWERSE-TR-2007-04

BibTeX:

@techreport{REWERSE-TR-2007-04,
	author = {Gastón E. Tagni},
	title = {An Approach to Complex Event Detection in the Web},
	institution = {Institute for Informatics, University of Munich},
	year = {2007},
	type = {{research report, REWERSE-TR-2007-04}},
	number = {REWERSE-TR-2007-04},
	note = {Master Thesis, Department of Informatics, New University of Lisbon, April 2007},
	url = {http://rewerse.net/publications/rewerse-publications.html#REWERSE-TR-2007-04}
}