At a previous job, there was lots of talk about "Enterprise Service Bus" (ESB). I read parts of a conceptual book about it, but never really understood how you would implement/integrate it in concrete terms. I'm familiar with SOA/queueing/directory services/etc. but I don't understand what exactly an ESB is.
Is it a concrete thing (service/server/broker/etc.) that you just hook all your apps up to it in different ways, or is it more just a conceptual way to design systems?
Any explanations or links to good examples would be greatly appreciated. Thanks.
Answer
It's a fairly high level concept of abstraction. The central concept is that the ESB provides the middleware and interfaces that allow businesses to connect their applications without writing code.
This could include mediation to reconcile incompatible protocols, data, and interaction.
The idea of a central bus on which everything passes gives opportunity for additional layers of abstraction. Using industry standards to "plug" other applications, clients, and such into this bus makes it so that connecting new services, data sources, clients with disparate needs is relatively easy.
Actual implementations
As far as actual implementations, that's the domain of very large enterprise support businesses. While it's very buzzwordy, the goal is an ideal that on some small level can be understood through comparison with the internet:
Similarity to Internet
One big communications bus with widely different uses and data, but all running standardize protocols.
One can, in fact, write an HTTP to FTP connector that would allow browsers to access FTP sites without invoking an FTP client (usually built into the browser now).
Mashups
Mashups demonstrate an interesting implementation - take some bus route data from the San Francisco authority, map from google, and sushi bar locations from yahoo with ratings and run a simple query that gives you the closest sushi bar, weighting it so that you'd be willing to travel a little further for a better bar.
All completely different services, incompatible by themselves, but using standard connectors (yahoo pipes, for instance) they can be pulled together into a cohesive and useful whole.
-Adam