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Subject: RE: [wsia] Can a producer make look & feel changes?
This thread of discussion has elucidated many interesting points about the value and drawbacks of both the property driven and stream oriented modifications to a service's output. Architecturally there is no reason to exclude one in favor of the other and discussions in the use case subgroup have brought out cases where one would be preferred to the other. Consider: - Need for a consumer to indicate the type of output a producer should generate (XHTML vs WML vs ....). Much easier with a property driven approach. - Desire of a consumer to supply input that the producer will use when generating its output (eg. a news service that a financial page wishes to configure for display with an End-User's portfolio ... with the news focussed on the portfolio items). Again easier with a property driven approach. - When wrapping a legacy web app, in many cases a producer can't (or won't) modify the app to use a property driven approach. The stream oriented adaptations then allow a robust means (as robust as the writer of the locators that point into the stream makes them) for a consumer to do things such as: - lookup values the producer has imbedded in the page - inserting related markup (such as cross-selling markup) - inserting content that is confidential between the consumer and the End-User - insert the validation or action processing desired by the consumer (eg. consider a consolidated shopping cart) As also mentioned by others, there are times when both the Producer and the Consumer wish to exert control over the markup (often for branding reasons). Supporting both means of modifying the markup allow the business entities standardized means to implement the choices made in their business arrangement. Eilon Reshef <eilon.reshef@webc To: "'Sean Fitts'" <sean@crossweave.com> ollage.com> cc: wsia@lists.oasis-open.org Subject: RE: [wsia] Can a producer make look & feel changes? 03/19/2002 11:27 PM > Just to clarify my earlier description with regards to your point below. The Consumer physically has access to the entire markup fragment, so when business arrangements permit, the Consumer can make any type of modifications to the markup. I guess one of the ideas we are trying to capture in the Customized scenario and in WSIA in general is an explicit well-defined interface that declares what are the customization options (and, possibly, and also arguably, how to implement them). The existence of such an interface (independently of the mechanism that's used to describe it) is implicitly assumed in many of the discussions, mainly for robustness reasons (the Producer is committed to support those adaptation points one way or another along application changes). Naturally, the interface can't capture all of the different customization options possible, only those predicted and supported by the Producer. It is then up to the business arrangements to define whether adaptations other than those defined in the WSIA interface are allowed (in which case the Consumer can freely play around with the markup), disallowed (in which case the Consumer can't do anything with the markup), or anything in between (e.g., allowed after a review by the Producer). I wouldn't suppose we - as a committee - can decide between those options; we can only come up with the interfaces and assume the business arrangements are taken care of. Hope that makes sense. Lastly, on the issue of property driven adaptation vs. markup driven adaptation, I wasn't present at the smaller group discussion, so I may be covering old ground. However, I have significant concerns about the property driven approach that extend beyond back-compatibility. To me, the property driven approach implies that the producer must predict all of the changes that a consumer may want to make (since they are responsible for implementing them). This may seem attractive from a Producer control standpoint (which I agree is an important issue), but I think it will have the effect of limiting the re-use of services. Certainly our experience to date suggests that it is very hard, if not impossible to predict the ways in which Consumers may want to adapt services and so I would argue we should err on the side of flexibility.
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