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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Are people really using Identity constraints specified in
 Peter, Here's how VAM works in CAM right now. We have a simple precedence sequence. Again - in order to remain sane - and to allow implementers of CAM engines and writers of CAM templates - to do stuff that does not require Teraflops of processing power or excessive tearing of hair out! Anyway - the VAM is this - base rules are those in-line rules embedded into structure members, (or included via an included structure). These are overridden by any rules that match the same XPath target(s) that are declared in the the <BusinessContext> section of the template. Third - the <ContentReference> section provides default rules (typically retrieved from the central registry, but can be in-lined too) - that provide rules if neither the structure or context section provides any. Last but not least there is the <DataValidation> section - this is mostly for external calls to webservices - and so again - anything failing these checks will be rejected with an appropriate error - this section is optional though - an intended for backend internal integration needs against the actual data content - rather than structural checks. VAM is certainly a key thing to have explicit. Thanks, DW Quoting "Hunsberger, Peter" <Peter.Hunsberger@S...>: > w3c@d... writes: > > > Thomas, > > > > When I read this I feel good about how we have engineered CAM. > > > > These real world examples show that we have it right - since > > it can handle all of this in its stride. 3 different ways of > > looking at one value? No problems. And context driven - yes! > > I don't think it can be emphasized too much how important context > sensitive validation is required. The real world requirements are > simultaneously local and global. Two main issues arise: > > 1) what is best practice for determining context? A simple hierarchical > mapping works for only some subset of the problem. A complete rules > engine is complex and expensive. Similarly, an Ontological traversal is > complex and expensive. > > 2) Normalization. Static XML templates don't easily provide a useful > degree of normalization. Given the lack of a clear path for my first > issue this may not seem like a real problem yet, but we're already > running into it. Our business analysts have dumped many requirements on > us to allow them to reuse already existing template fragments (we use > them for presentation, styling and validation) across multiple contexts > when a portion of the template is identical. > > Currently for 1) we use a simple XSLT based rules engine traversing > multiple XML hierarchies. I know where I want to go with this and I > believe I can keep the processing costs reasonable and get an 80% > solution. The solution to 2 is joined at the hip with 1. As you > traverse the rules graph you locate pointers to the template fragments > needed to create the entire template; start globally, traverse to local, > (recursively use rules to determine how to combine the results). > > The implication for CAM is that, long run, you also need a VAM: a > Validation Assembly Mechanism. This may seem like overkill, but I > really think this is a multiple dimensional problem with the same > solution over each dimension: triples driven graph traversal. > > An interesting side effect of looking at the problem this way is that it > gives you a precise definition of ambiguity. Ambiguity arises when the > traversal over each dimension does not arrive at a single point but > rather some higher order space (be it 2D, 3D, or whatever). If you > arrive at such a space you have to either have defaults or a way to > alert some portion of the organizations involved that they have not yet > agreed on a workable solution; (local augmentation of the rules graphs > is likely the near term fix...). Now if only we really knew what each > dimension was (Zachman's architecture framework anyone ?: > http://www.zifa.com/). Clearly, MVC only captures a small portion of > the problem. > > > > > Sure people can bitch about this not being 'simple' - but the > > kind of use cases you have shown only proves you need strong > > adaptability and flexibility to solve these real world needs. > > > > Fortunately - unlike Tim's thoughts on XQuery - I feel very > > confident that CAM has managed to address the needs. > > > > It appears you're doing very good work on one portion of the problem. > However, watching the various standards chasing each other in circles > around the world, feeding on vast amounts of human resources, growing > ever fatter, and continually failing to simplify my life doesn't make me > have quite your confidence. > > > ----------------------------------------------------------------- > The xml-dev list is sponsored by XML.org <http://www.xml.org>, an > initiative of OASIS <http://www.oasis-open.org> > > The list archives are at http://lists.xml.org/archives/xml-dev/ > > To subscribe or unsubscribe from this list use the subscription > manager: <http://www.oasis-open.org/mlmanage/index.php> > > 
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