A versatile event notification service

1
A versatile event notification service
Motivation Event notification servers are used
as the basic middleware infrastructure for
software systems in a vast set of application
domains (e.g., user and software monitoring,
computer-supported cooperative work, awareness,
workflow management, mobile applications, etc.).
Event notification servers implement a
distributed publish/subscribe service, allowing
information producers to publish events, while
information consumers subscribe to and receive
events of interest as notifications. Subscribers
express interest in a subset of events through
the use of content-based queries called
subscriptions. These subscriptions are handled by
the notification service that routes events from
consumers to interested parties as the events are
produced in the system. The increasing popularity
of this paradigm has created demands for new
functionality exceeding the simple publication
and subscription of events. Current commercial
and research infrastructures address this problem
by developing infrastructures with specific
functionality. These implementations, however,
provide poor extensibility, configurability, and
support for dynamic change, making those
solutions not versatile enough to support various
requirements. Up to now, developers have had
basically three options when choosing an event
notification service to support their
applications 1. Use one-size-fits-all
solutions such as CORBA Notification Service
(CORBA-NS) or READY.
2. Rely on application-specific notification
servers, such as Khronika and CASSIUS, for
example, which are specially designed to support
groupware and awareness applications or even
Yeast and GEM, which are specialized,
respectively, for advanced event processing for
locally networked applications and for
distributed applications monitoring.   3. Use
more generic but simpler notification servers,
such as Siena and Elvin, which provide simplified
content-based subscription and Internet-scale
support. All these solutions provide poor or no
support for selection and customization of the
services required by each application domain, a
feature that is important in the context of
constantly changing and evolving applications, or
in large organizations, where different
application domains need to be integrated.
Versatile Event Notification Service Our
research focus is to address these problems by
providing an extensible and configurable
architecture for the implementation of
domain-specific event notification services.
YANCEES (Yet Another Configurable and Extensible
Event Service) provides a common framework based
on extensible event, subscription, notification,
protocol, and resource models, over which
different configurations, with functionality
demanded by heterogeneous application domains,
can be developed. Extensibility is provided by
the combination of plug-ins and extensible
languages. Configurability is achieved by the use
of configuration managers, while dynamism is
provided by dynamic parsers.
Figure 1 Yancees enhances publishers and
subscribers with plug-ins and languages that
provide a versatile platform for supporting a
large set of applications.
2
Extensible Architecture Yancees dynamism and
architecture rely on the combination of
extensible languages, defined in XML, and
plug-ins. The new functionality defined in a
language is matched by plug-ins installed in the
server. Dynamic parsers combine existing plug-ins
in expression evaluation trees that address the
specific requirements of each subscription. This
approach allows the allocation of resources
according to the subscribers need, besides
promoting the reuse of plug-ins. Yancees core
functionality is built upon current content-based
publish/subscribe systems as Siena, Elvin,
CORBA-NS and others. This approach enables
compatibility with and integration of different
event notification networks. Current Status The
core functionality illustrated in Figures 1 and 2
are currently available. YANCEES currently
extends Elvin and Siena notification services and
provide Java RMI integration. Future
implementations will include support for web
protocols (Web services), server-side plug-ins
providing most functionalities found in current
event notification services, including mobility
and awareness support client-side plug-ins,
including graphical subscription editors and
components, and integration with current software
development tools such as Eclipse.
Figure 2 Plug-ins, filters and services
implement the functionalitydemanded by the
notification, subscription, protocol, and
eventmodels, achieving the versatility demanded
by new applications
Figure 3 Parsers dynamic allocate plug-ins to
provide thefunctionality demanded by each
subscriber
Effort sponsored by the Defense Advanced Research
Projects Agency (DARPA) and Air Force Research
Laboratory, Air Force Materiel Command, USAF,
under agreement number F30602-00-2-0599. Funding
also provided by the National Science Foundation
under grant numbers 0083099, 0205724, and
0326105 and CAPES (grant BEX 1312/99-5). The
content of the information does not necessarily
reflect the position or the policy of the
Government and no official endorsement should be
inferred.
Contact Information Professor David F.
Redmiles Roberto S. Silva Filho Cleidson R. B. de
Souza Information and Computer Science University
of California Irvine, California
92697-3425 redmiles, rsilvafi,cdesouza_at_ics.uci.
edu 949-824-3823, 4121, 7308 949-824-1715
To learn more about YANCEES and have access to
a prototype of the system and documentation,
please visit the website http//isr.uci.edu/proje
cts/yancees
December 2003