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Subject: Re: [wsbpel] Issue 11 - Call for Discussion
Yaron Y. Goland wrote:Looping to construct a variable is a good example of where the atomicity of <assign> is insufficient to hide the intermediate stages you are concerned about. This could be addressed in several ways:
Is there a requirement that variables be schema-valid during all stages of variable manipulation? Or should the requirement be the looser "variables should be schema-valid when used (directly or indirectly) in a message sent by <invoke> or <reply> activities? Or is there a more useful requirement in the arena? The assign mechanism, in all its various forms that we have seen in this forum, is essentially a piece of imperative code embedded in a declarative process model. This does introduce some form of "impedance" mismatch. However, I think you are overstating the problem by suggesting that this is too difficult to address. Imperative logic that manipulates any kind of structure will always introduce transient states that are illegal / nonsensical; this is a problem that has been with us since t = 0. :-) This is also a problem that has been addressed in the past, where t ≥ 0. Leveraging existing standards is a Good Thing, but being insufficiently prescriptive can harm portability. Leaving this completely open to the whim of BPEL engine providers harms the utility of the BPEL spec in this regard. (I believe the proposal Danny has put forward leverages the existing W3C DOM work to a high degree.) -Ron |
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