What are the responsibilities of an Orchestration engine vs a Message Driven System.
If I have to build a system which have to string together different independent components(cross-technology/platform components which need not expose a web service end point), which is the toolset to be chosen?
Is there a better option?
While this question is tagged Java, I'm afraid to say the best tool I've seen if you really have to go this route is Microsoft's BizTalk Server.
When I had to do an evaluation of this type of product (and this was a few years back) it was head and shoulders above the competition with the main features being:
In the end we choose to keep-it-simple and went the messaging route, although this does require you've got control of all the participants, which may not be the case.
Use openESB with netbeans editor or any other open source BPEL engines which provides standard way or orchestrating the process. if you think performance is very important than standardization you can try out some proprietary ESB or BPM tools like Jboss jBPM or mule ESB etc.
Please note BPEL can be used only to consume Web Services if your components are not web services then you may have to use some ESB like Mule which can support some 200+ protocols with extensions.
When deciding if you should use Orchestration or Message Directed work flow, the big question you face is, do you think it will be necessary to change your orchestration work-flow on a regular basis. If you think the Business Process needs to be flexible because it is subject to change, then adopt a Canonical Message format and use Orchestration which will minimise he impact of changing relationship between service. If you think the work-flow is stable you can adopt a message driven work-flow.