Web service platforms take root in enterprise: move toward event-driven architecture predicted

America's Network, Nov 1, 2004 by Fiona Chau

"SOA can be implemented using an asynchronous publish-and-subscribe approach or with a broker mechanism that dishes out messages to the appropriate service. From this perspective EDA can be viewed as a subset of SOA--the component of SOA that deals with event-based messaging," Glikson says.

Standards needed

One marked difference between SOA and EDA is the lack of standards for event-driven systems. While event notification has been part of the SOAP protocol from the start, it doesn't provide all of the details necessary for an event-driven publish-and-subscribe environment, which not only raises implementation issues between different Web services products, but also interoperability issues between SOA and EDA.

Industry players and standard bodies like OASIS are already addressing this through several standardization initiatives.

EDA vs SOA at a glance

EDA                                 SOA

Based on real-time events, mostly   Demand-services based (e.g.
asynchronous and unpredicatable,    request for information) i.e.
typically models are long-running   mostly synchronous
business processes

Clients and servers decoupled       Clients and servers loosely
                                    coupled

Many-to-many publish/subscribe      One-to-one request/reply (Pull)
(Push)

One-way guaranteed event delivery   Bi-directional, but no delivery
                                    guarantee

Ideal for parallel processes,       Ideal for sequential or straight
events (triggers and joins) and     through processing and composite
exception handling across           applications where all associated
disconnected systems                systems and services are available

Standardization is in progress      Basic standards are maturing, and
with services standards being put   now the next frontier is to evolve
into place to address EDA           and support standards for EDA

Uses event descriptor metadata      Uses interface metadata

Sink (recipient) determines flow    Client directs flow

Can react to new external input     Closed to unforseen input once a
while process is light              flow is started