Event-Based System for Generation of Traffic Services in Road Congestions - Foundations on Natural and Artificial Computation - page 204

Fig. 2. Event flow among main entities of the system

of situations at each consequent time. More complex events are formed from the
collection of more entities and their relations. Complex events are built from
simpler events, applying analyzes of complex pattern detection, correlations,
hierarchical rules and temporal relations of cause and belonging.
For the implementation of CEP modules in trac centers, it was decided
to employ Esper [5], a CEP/ESP engine in open code, implemented in Java
and currently available over GPL license. Esper brings its own language for EPL
queries (Event Processing query Language) based on SQL. Apart from launching
continuous queries about event flows, this language makes it possible to launch
triggers if a pattern has been detected in the event flow.

4 Trac Congestion Detection Services

Open Geospatial Consortium (OGC) defines a series of standards for web-based
services exploiting geographical information based on non-proprietary Internet
standards, such as World Wide Web (WWW) of HTTP, Uniform Resource
Locators (URLs), Multipurpose Internet Mail Extensions (MIME), Extensible
Markup Language (XML) and other standards related to web-based services such
as WSDL (Web Services Description Language) or SOAP (originally standing
for Simple Object Access Protocol). These standards include Web Map Service
(WMS) and Web Feature Service (WFS), employed in the implementation of
the trac center system under consideration.
WMS service produces dynamically a map with spatially referred data. This
standard interprets a map as a representation of geographical information over
a digital image file, and not the data themselves. Following this, trac center