T he enterprise service bus (ESB) is a hot topic today. Many vendors are either building new products in this category or dressing up their existing products to pitch as ESBs. However, there is no clearly accepted definition of what an ESB is, what its architecture should be, or what its programming paradigm should be. Definitions range from saying that it is nothing and wholly unneeded to saying it is everything and has all the capabi- ties of a full integration suite with built-in orchestration, data aggregation, and web services management capabilities. Architectures range from being...