Integration

I'm fairly new to ESB and BPEL, and am a little confused on one issue, where to do transformations. I read in "Wiring Through an Enterprise Service Bus" that transformations should be done in BPEL to remove any business logic from the ESB, but in a lot of the use cases I see, the transformations are being done in ESB. Is this more of a question of preference and performance, or does it really depend on the situation the data is being transformed in.

Basically I have a legacy system, whose messages get posted to a queue, that message is to be transformed into a canonical format, then from there get transformed again into the destination system's schema. I would think this would be most easily accomplished in ESB rather then BPEL.

Any insight is appreciated.