>
> Perhaps we just disagree about how often interface changes are
> required in practice? In my experience (yes, I do have considerable
> experience with this approach 8-), it's *very* rarely necessary when a
> fully generic interface is used.
>
To me, this is not a technology issue. It's a recognition that in
the real world, things change. Any approach that tries to avoid
change is going to be more problematic than an approach that embraces
change.
If I have a generic interface that returns any valid XML message, all
I've done is push the logic that must turn that XML into something
meaningful out to the endpoints. If I have multiple consumers, each
consumer may now perform that logic differently. If the underlying
XML changes, which it will, each of the consumers that requires that
data will need to be touched. With no consistency on how that is
done, the cost of implementing that change is far higher than if the
service interface accurately described what was being exchanged. We
can employ techniques to maintain backwards compatibility to ensure
that only interested clients are impacted.
By advocating rigid stances that interfaces won't change, we set
ourselves up for failure when things do change. I'd much rather have
the development teams understand that things will change, and as a
result, they should embrace mature release management practices
allowing the change to be addressed in an organized, rather than
chaotic manner. I'll be the first person to admit that this is an
extremely difficult thing to do. Given the blurring of boundaries
that will occur with SOA, this will become more and more important.
Personally, I think we will we reach a point where an organization's
release and change management maturity will be one of the largest, if
not the largest, differentiator between the top tier of SOA adopters
and the rest of us.
-tb
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