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Subject: RE: [wsbpel] Issue - 152 - New Proposal to Vote
Ron, The idea for option 2 is to declare the
reference scheme, which could be at the process level. In addition it can be declared by any activity
(which would then change the default for its children) similar to the suppress
join failure and query language attributes. This way one can declare a reference scheme
at the process level or a scope or an assign, etc. In this scenario, a BPEL4WS 1.1 process would
not change unless it used an assign to/from a partner link. In that case the process would simply
declare a <process reference-scheme=” http://schemas.xmlsoap.org/ws/2004/08/addressing” attribute. Also this seems more consistent with bpel’s query language support, which also declares an
external language dependency. Although
in the reference-scheme case we won’t have a default. You are right about EPR sources. Although in addition I could for see your
option number 1 being extended. For
example the process itself could be dealing with a “purchase order”
and the vendor’s EPR is looked up in a database via an invoke activity,
so it may not be exactly hard-coded. Also the scenario where one wants to look
at the EPR data in the process is easily accomplished. The reference-scheme declaration would
allow one to copy data from a partner link to a compatible message part or
element thereby allowing the policy use-case you described. In the service-ref case (the current one
we are debating) you never know as an implementer what you have under the
service-ref element. - Chris From: Ron Ten-Hove [mailto:Ronald.Ten-Hove@Sun.COM] Chris,
As you say, EPRs should hardly
affect the process logic itself. It would be a very odd process indeed that
needed to query the reference scheme as part of the business process. That
being said, one could imagine some scenarios in which certain aspects of the
EPR affect the logic of a business process, in an attempt to build some sort of
basic policy mechanism (eg, no sending sensitive messages to endpoints via
insecure transports). I should hope that this would be a very uncommon
practice! My feeling is that a reference-scheme
attribute is a good idea, although maybe not in a service-ref. For the
majority of cases it doesn’t affect the actual BPEL at all. The
reference scheme is typically between the engine and its receiving/invoking
layer(s). It never even shows up in your BPEL file unless you hard code a
literal to map to a partner link, which in my opinion is unlikely to be used
much. If a partner link is truly associated with a dynamic address then
the reference will be returned as the result of a service invocation (which may
call a database for instance). Also the idea that a scheme must have a
uniform root element to encapsulate it seems unnecessarily restrictive. I
can easily imagine a scheme where the content of the reference is a directory
location for looking up the service provider. In that example my scheme
would be reference-scheme=”http://.../ldap-reference”.
In my opinion the content model should not be forced to have one element with a
unique namespace. I actually have 2 alternative proposals,
but prefer option number 2. 1 – Make the reference-scheme a
required attribute. I use the same argument as was used for including an
import type in the bpel import, so one did not have to open up the import in
order to know how to handle it (or not for that matter). Suppose I
execute a service to lookup a service reference the bpel engine has to know how
to deserialize it and when an activity using it is called then there may be
more than one receiving/invoking layer which it may route it to. My
preference in an implementation would be to look at the root of the element to
know how to unpack it rather than peek in. We also need a
runtime fault like bpws:invalidReferenceScheme when an engine figures out that
it can’t handle a reference which has been moved into a partner. 2 - If a bpel process uses assigns to
partner links then we should require a reference-scheme attribute at the root
of the bpel process (or in an activity level) like query-language. Unless
this attribute is set assigns to Partner Links will not be allowed. This
eliminates the need for a reference-scheme attribute in the service-ref
itself. This way an engine won’t try to run a bpel process, which
utilizes a scheme it doesn’t handle. Then we don’t need a
bpws:invalidReferenceScheme, which is thrown after the poor user has already
done a lot of work and then realizes it isn’t any good. In this
case we don’t need to describe a service-ref at all since the bpel process
and static analysis can figure out if it is an improper assignment. Hope this helps, Chris |
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