Title:
If BPEL were to be strictly a modelling language, then the inclusion
of both <sequence> and <flow> would be justifiable from the modelling
perspective. Perhaps we can make this claim for abstract BPEL?
On the other hand, "concrete" BPEL has a different purpose: it is an
executable description of a process. It may be appropriate for the
TC to create a formal semantics for the execution of each BPEL element, in
order that we may analyse and better understand what we are creating. Even
if we don't go as far as formalising the semantics, it is true that the simpler
the language, the easier it is to reason about. From this perspective, it
is entirely appropriate for Arkin to ask that the <sequence> activity
justify its existence, when equivalent structures exist elsewhere.
So what is our rational moving forward? Is this (primarily) a modelling
language, or an executable artifact? Or are there better criteria for resolving
these issues?
-Ron
Assaf Arkin wrote:
I agree.
If the distinction was made between doings thing in order or in parallel,
then I understand why you need two different activities. But we wouldn't
need links or serializable scopes. Currently the flow activity covers all
the cases from strictly serialized to strictly concurrent and all shades
in between, making the sequence activity nothing more than a convinience.
You need to support the complexity of synchronized activities to support
the flow activity, that's not easy but if you have the capability you might
as well use it all the way.
So the sequence activity does need to justify its existence, and it needs
a generic rational so we can decide what to do with other existing or proposed
"simplifications" to the language.
arkin
Eckenfels. Bernd wrote:
Hello Satish,
I honestly don't think <sequence> needs
to justify its existence.
Concurrency with synchronization can emulate sequentiality but that is
clearly a convoluted and expensive way to do the simplest kind of
orchestration.
This may be true from the standpoint of writing bpel by hand, but for sure
it is a non issue for implementation. Depending on your internal runtime
data model, a sequence is only an additional complication, provided the fact,
that you need to offer a implementation for flow, anyway. And since a sequence
does not forbid to have links in and out, it also means your engine has to
support the notion of synchronisation, anyway.
So we should make clear in the spec, that it is only a shortcut, for skipping
those links inside a sequential flow, but all other properties will apply,
anyway.
Greetings
Bernd
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