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DEBS08(5) - Event-based Constraints

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Old 07-07-2008
DEBS08(5) - Event-based Constraints
vincent
Mon, 07 Jul 2008 12:41:24 +0000
Another paper at the Distributed Event Based Systems conference was on “Event Based Constraints for SensorNet Programming”. I had high hopes for an interesting paper on goal-driven CEP, but in fact the authors (from Brown University, USA) seemed to define “constraint” as a synonym of “filter” (as in “temporal, spatial, attribute-based or existential constraints on some event”). So there was no CLP-type relaxing of constraints during event processing to try and achieve some goal.
The paper did describe some an interesting approach to distributed CEP, using spatial and temporal event processing elements to divide up a high-datarate environment (detecting people being chased in a crowd). The main problem was, as always in distributed event processing (without a shared memory bus), ensuring that all possible event correlations can take place (with the right event being in the right processor at the right time). Probably for some sensor processing, though, a 100% success rate is not a requirement (i.e. if someone runs across an “event process boundary”, they will be presumably be picked up by the next event processor at some point).
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LEARN ABOUT DEBIAN

event::generic

Event::generic(3pm)					User Contributed Perl Documentation				       Event::generic(3pm)

NAME

       Event::generic - generic event handling

SYNOPSIS

	use Event::generic;

	$source = Event::generic::Source->new;

	$w = Event->generic(source => $source, ...);
	$w = $source->watch(...);

	$source = $w->source;
	$w->source($source);

	$source->event;
	$source->event($data);

	$data = $event->data;

DESCRIPTION

       This module provides a watcher type within the "Event" framework.  You must understand the architecture of the "Event" system in order to
       understand this document.

       This module provides a system of reified event sources and watchers watching those sources.  Events are generated solely by a method on the
       event source object.  The events may carry arbitrary data to the event handler callbacks.  This module is intended for situations where the
       events of interest are best determined by Perl code.

CLASSES

       Event::generic::Source
	   A reified event source.

       Event::generic
	   A watcher that can watch "Event::generic::Source" event sources.

       Event::Event::Dataful
	   A (target) event that can carry arbitrary data.

EVENT SOURCE CLASS

   Constructor
       Event::generic::Source->new
	   Creates and returns a new event source.

   Methods
       $source->event
       $source->event(DATA)
	   The invocation of this method is a source event for watchers of the event source.  When this method is called, each active watcher of
	   the event source generates a target event.  The DATA, if supplied, is copied into the target event objects, from which it can be
	   retrieved using the "data()" method.

       $source->watch(ATTR => VALUE, ...)
	   Generates and returns a new watcher, configured to watch this event source.	The standard watcher attributes may be specified as
	   arguments.  The watcher returned is an ordinary "Event::generic", and may be reconfigured to watch a different event source.

WATCHER CLASS

   Type-specific attributes
       source => $source
	   The event source to watch.  This must be either an "Event::generic::Source" object or "undef".  When set to "undef", no source is being
	   watched, and the watcher cannot be started.

EVENT CLASS

   Type-specific methods
       $event->data
	   Returns the data associated with the event, which may be any scalar.  This is read-only, and is set by the event source.

SEE ALSO

       Event

perl v5.14.2							    2007-05-22						       Event::generic(3pm)