On Wed, 22 May 2002 14:32:10 -0700, [EMAIL PROTECTED] wrote: > > Torsten, > > I guess it depends on what one means by constraint. XForms allows > constraint dependency rules described using XPath. So if you have > two fields, "CLASS_RANK" and "CLASS_SIZE" you can (I think) write a > rule that says "value of CLASS_RANK must be less than or equal to > CLASS_SIZE", i.e, something like: > > <xforms:bind ref="instance/CLASS_RANK" isValid="current() > <= ../instance/CLASS_SIZE" /> > > But even if you have such an XPath expression, it's just text to a > parser-- nothing to parse. And so, very difficult to translate into > javascript. If instead you have a regex constraint you don't need > to parse it, just drop the string into a javascript object and > create the handlers that call the right method..
I agree. XPath translation to JavaScript would essentially mean implementing a full blown XPath processor in JavaScript. But perhaps a better approach is to make use of the JXPath engine, which is an XPath processor working on Java beans or DOM trees, and have it execute the constraints. The JXPath based implementation however would work on the server side only, for complex client side validation you're still left with no support. But see below for an idea. > Anyway, I need to handle forms that have much more complicated dependencies > than the simple CLASS_SIZE/CLASS_RANK example given. Such dependencies > are easy to "describe" in javascript, difficult to describe in > XPath/Schematron. > So now I'm thinking about some kind of "ur-language" Quick question: what is "ur-language"? > for describing dependency (and other?) relationships, abstract > enough to be translateable into Schematron rule markup, javascript > procedural code, or whatever else is needed. I don't have an example handy, but in the case of constraints that need to apply on one-to-many type of relationships, it might be very difficult to do it. You might need to have "for-each", "if" and other normal programming language constructs to express these dependencies and constraints. SQL reference integrity checks are the closest examples for such dependencies. Perhaps the easiest way to deal with such problems is to split the solution: use simple schema validation to express how individual values should look like, and describe more complex dependencies in a normal programming language like JavaScript. With continuations-based flow control of pages, where form input is collected in JavaScript variables, is very easy to implement this higher level validation right in JavaScript. For the client side, the data collected at every point in the multi-page form can be placed inline as part of a script to be loaded in the client browser. The same validation functions that operate on the server side can then be executed on client browser, if this is desired. Of course there are lots of details that need to be figured out. Perhaps a good idea at this point is to see some realistic requirements, so if you have an example you could share with us it would be great. Regards, -- Ovidiu Predescu <[EMAIL PROTECTED]> >>> I'm in the job market again, check out my resume and qualifications at: http://www.geocities.com/SiliconValley/Monitor/7464/ (Apache, GNU, Emacs ...) --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, email: [EMAIL PROTECTED]
