In web applications, if you are able to do smt with html, then you won't use jsp and so on.. The rule of thumb is if you could carry out smt with a lighter,simpler technology, then choose it (at least i treat in this way). So, when we should choose bpel and when we should avoid using it and go on with ordinary web services?
this issue had been discussed here:
this evaluation is worth to note down: http://jeff-davis.blogspot.com/2007/08/whats-wrong-with-bpel.html
it has not bothered me before, but it seems that if bpel is necessary and completely handles bpm was also a controversial issue.. this is a famous article on this: http://www.infoq.com/articles/bpelbpm
btw, the title of this post is copied from here: http://dltj.org/article/bpel-in-fedora/, such a funny title:)
to sum up, i am still not sure when to use bpel :( however, now i am aware of the ongoing debates.. in fact, i also want to spend time on understanding if xml is only for data and xml should not be used to program, before going further with bpel..