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From "Zubin Wadia" <zwa...@gmail.com>
Subject Re: Backward compatibility of compiled processes and live instances
Date Wed, 14 Nov 2007 18:24:36 GMT
Just to contribute, this is the IBM perspective on it:




On 11/14/07, Alex Boisvert <boisvert@intalio.com> wrote:
> Hi devs,
> We gathered at ApacheCon this week and yesterday discussed the thorny
> issue
> of long-term process instance compatibility.  The question, to put it
> succinctly, is how to continue the execution of live instances of process
> definitions compiled on previous versions of Ode into future versions of
> the
> software, despite changes and improvements to the engine.
> After discussing several alternatives, we are proposing the following,
> 1) For identification and tracking, we would encode an O-model version
> number in the compiled BPEL process files;  existing .cbp files with no
> version are assumed to be version 1.
> 2) We would keep and maintain different versions of the process definition
> model concurrently in the source tree.   Each version would be kept in a
> separate module with different package names to avoid name collision
> during
> serialization/deserialization, as well as to support concurrent class
> loading in the same engine.   It would be possible to compile processes
> into
> a specific O-model version by selecting which compiler version to use.
> 3) For convenience, we would bundle together the "
> org.apache.ode.bpel.runtime" package, the O-model and the compiler into a
> single module.  This would simplify comparing and tracking changes between
> versions.   (This would require some refactoring to handle compile
> dependencies)
> 4) The latest version of the O-model in trunk would always be considered
> under development and "unstable".  In other words, fair game for
> modification.  Only after an official release would this model be
> supported
> with respect to forward-compatibility, and at that point we would "freeze"
> this version and create a new one for future development.   By default,
> the
> engine would compile processes using the latest stable version.
> 5) At this point in time, version 1 is embodied by the O-model currently
> in
> the 1.1 branch, and version 2 is what's under development in the trunk
> now.
> We would therefore merge back the O-model from the 1.1 branch into the
> trunk
> to support both concurrently.
> 6) To keep the number of supported O-model versions to a manageable level,
> we anticipate to release new O-model versions every 6 months to a
> year.  The
> actual frequency would depend on developer and user interest, as well as
> the
> type of changes required for new features.  To strike a balance between
> backward compatibility and enhancements/progress, the project would
> concurrently maintain and provide support -- on the same Ode server
> instance
> -- for a "window" of O-model versions covering approx. 2 years [1].  It's
> anticipated that commercial vendors will be encouraged to provide
> longer-term support ;)   Older O-model versions would be supported on
> older
> versions of the server for a longer period, based on community involvement
> and interest.
> Feedback and questions are very welcome!
> Alex, Assaf, Maciej, Matthieu
> [1] We generally recommend breaking down long-running processes into
> shorter
> ones in order to support agile process improvement and change.  It's also
> wise to consider modeling long-running process instances as persistent
> external entities, as this approach generally offers higher levels of data
> and state manageability ( c.f. External Variables).

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