Event Driven Architecture (EDA) is a style of software architecture based on real time flows of (you guessed it) events. EDA is a buzzword was being pushed by Gartner as far back as 2003. At the time, Roy Schulte of Gartner went so far as to say that in SOA, connecting services occurs in a linear, predictable sequence, whereas an event-driven architecture allows for multiple, less predictable, asynchronous events to happen in parallel and trigger a single action.
Not that many folks got excited about EDA as a buzzword (most seem to think it's just part of SOA), so Gartner Analyst Yefim Natis teamed up with Oracle to coin the phrase SOA 2.0 (which appears to be another way of reintroducing EDA) another term which got a few folks excited, but not in a good way. Despite the criticism (Mark Little of JBoss posted a notable criticism), EDA enthusiasts continue to develop architecture.
Whatever it is ultimately called, dynamic real-time systems involving the integration of services will continue to be of interest to SOA practitioners. An excellent article about Event-Stream-Processing tools (ESP)is provided here. This article states:
ESP enables an event-driven SOA to decipher causal (if A is followed by B followed by C), temporal (within four seconds), and spatial (within 10 feet) relationships among events - and can do so in real-time. This kind of "enterprise wiretap" lets a business continuously analyse key performance indicators in real-time, identify threat and opportunity in real-time, and act instantly. These capabilities require a new style of computing - stream computing - that can deliver the missing link between an event-driven SOA and real-time business insight.
The introduction to the article is savvy enough to point out that existing terms such as SOA and Enterprise Service Bus (ESB) are capable to answer these needs, but the article goes on to describe a well researched set of concepts that are in application at some large companies. Another article details how to implement EDA using Mule, an open source ESB.