Event Driven Architectures

Came across a pretty cool open source product several weeks ago. It's an event stream processing engine called Esper developed by a couple guys who look like they have a lot of experience building systems for the financial sector. Makes sense since I can see a lot applications for EDA's in the financial domain. Esper defines its own EQL (event query language) that allows you to define SQL-like expressions to process against the stream of events coming in. Thus you can use EQL to define rules to correlate the events that are passing through. The thing I like about this product is its ability to take in XML messages as events. You can use XPath to define the properties of those XML-based events and then reference those events and properties in your EQL expressions. This has a lot of applicability in Web Services and ESB-based systems where you have a lot of XML messages being passed around. This could probably be used to implement the supply chain ESB scenario that I wrote about in this article.

EDA, esper