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Subject: Re: [wsbpel] implicite links of the runtime engine (was: Implicit<sequence> macro)


Satish Thatte wrote:

>All true, except for the simple matter of analyzing the implications of
>concurrency for access to shared data or being able to recognize the
>patterns where concurrency is absent and thus concurrency control is not
>required.  In particular, if a sequence has incoming and outgoing links,
>and is now replaced with a flow with links itself, I submit that
>recovering the original pattern and its simple inexpensive
>implementation would be challenging.  
>
This type of analysis should be done, regardless of whether <sequence> 
is used. Further, it is not that difficult to distinguish sequential 
chains of activities, if one models the process as a (suitably 
annotated) DAG, rather than an XML tree.

(Control of concurrent access to process instance state is a topic we 
need to delve into separately. Is there such a thing as a "safe" BPEL 
process, in this regard? Can we create a formal semantics of execution 
to aid in verifying safety properties?)

>
>In other words, we would be raising the bar for implementers of both
>tools and runtime engines, especially if we expect them to cater to the
>prejudices of those who prefer the "block structured" approach rather
>than the "linking activities" approach that Assaf seems to like these
>days.
>
I'm not sure I understand this final comment. Eliminating <sequence> 
does not change the basic topology of such process graphs.

As for "raising the bar" for implementors: I'd issue the standard word 
of warning about "premature optimization." As a colleague of mine is 
fond of saying, we have to paint the dragon before we can slay it.

Cheers,
-Ron




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