WebLogic Event Server and WebLogic Server: What's the difference?

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Seth White's Blog | September 18, 2007   8:46 PM | Comments (0)

I had the chance to speak with a number of people -- developers, managers, consultants, and architects -- who stopped by the Event Server booth last week during BEAWorld in San Francisco.  I would like to say "Thanks" to everyone who took time to watch the Event Server demos and ask us questions.

One question that I heard come up in various forms at the booth was "What is the difference between WebLogic Event Server and WebLogic Server?".  Many folks were hearing about the Event Server for the first time and wondered if the Event Server was a layer of software that ran on top of WebLogic Server (WLS) or if it was a special version of WLS. These seemed like very reasonable questions -- after all Complex Event Processing (CEP) is a relatively new area for many people and the Event Server is a new product -- the first version, WebLogic Event Server 2.0, was released in July this year.

One of my previous blog entries, WebLogic Event Server and mSA,  touched on these questions somewhat.  The Event Server is best thought of as a separate software stack from WLS.  The Event Server is based on BEA's mSA architecture, however, so it is a completely modular server whose modules come from different sources, including the open source community.  As it happens, one source for the modules that are included in the Event Server is actually WebLogic Server.  But wait a minute, I just said that the Event Server was a separate piece of software from WLS, what's going on?

Some of what's going on is historical.  WLS predates mSA.  WLS contained a lot of cool stuff though, like JDBC connection pooling, and it made sense to turn those subsystems of WLS into mSA modules and reuse them in products like WebLogic Event Server.  So, the Event Server does contain pieces of WLS, but for the most part it's a different piece of software and a different application server.

There are many other differences between the Event Server (WL EvS) and WebLogic Server (WLS).  One is the application programming models that each support.  WLS supports J2EE as its primary programming model in addition to frameworks, like Spring, that make using J2EE easier.  The Event Server has a programming model that is based on Spring, but the Event Server's programming model extends the basic Spring programming model so that it provides a real-time container for complex event processing.  The most obvious extension to Spring is the CEP engine itself.  The CEP engine supports a SQL-based query language, called the Event Processing Language (EPL), for filtering, joining, and correlating real-time events.  Other extensions to Spring include custom tags for configuring the Event Processing Network (EPN) that makes up an application and dynamic configuration metadata for application components, among others.

Another thing that differentiates the Event Server and WLS is the types of applications that each application server hosts.  Most of the applications today that run on WLS are Web applications that human users interact with using a browser although, to be sure, there are a number of Web service apps and JMS apps also.  The Event Server, on the other hand, is an application server for hosting purely event driven applications.  Event driven applications are driven by other remote systems that generate events, like trade events from a stock exchange, instead of through human interaction with a browser.  The interaction between the Event Server and the systems that supply events is typically one-way, instead of the request-response style of interaction that is common for Web and Web service applications.  Event driven applications typically consume events from input sources and publish events or generate actions, such as triggering a BPM workflow, to a different set of output sources.

These are the major differences, but there are many additional things that could be mentioned such as the fact that the Event Server is designed for applications that have strict latency requirements.  This should be enough to give a general sense of how these two application servers stack up.

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