[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: [schema] which assertions can't you express ?
Chiusano Joseph wrote: > Philippe Poulard wrote: > >>hi, >> >>An XML Schema is the expression of some assertions expected on an XML >>document class. > > > That's an excellent definition, one of many possible definitions. > > >>Assertions on XML documents ensure that applications >>will process them without causing faults. > > > If by "them" you mean XML documents, yes then that would not be true, as > there are many other factors - for example, did the schema i wasn't talking about a schema, but about assertions expected, that some may be express in a schema, others in programs cover all of > the required validations per the requirements (those that XML schema is > capable of covering)? And then there may be requirements that XML schema > cannot cover, some of which you discuss below. > > >>Expressing assertions with >>schemas ensure that applications developpers will spend most of their >>time in designing data process and few of their time in controlling them. > > > Again, it depends on the requirements and what is required beyond what > XML schema can handle and therefore may have to be enforced in > application code, database triggers, etc. > well, i don't talk yet about implementations, just about kinds of assertions, in the aim to draw up the list of those that could be expressed in a schema, and those that is a matter for applications however, when one thinks about xml documents all along their process chain, one may expect that the schema may cover some assertions at a time and others at another time, according to the life-cycle of the document, given by some accessible datas ; that's a requirement, i think ; an alternative solution is to have an external schema selector, that chooses the right schema from a set > >>Any schema technology is designed to cover numbers of assertions >>expressed. However, if think that the existing schema technologies (DTD, >>W3C XML Schema, Relax NG, Schematron) can't express some constraint types. > > > Speaking only for XML Schema, that is true. > > >>I have some ideas of what these constraint types might be, but I'd like >>to know, helped by your own experiences, which kind of useful assertions >>can't be expressed with these schema technologies (so frustrating). >> >>For example : >>-i'd like that the number of occurrences of an element is equal to a >>value of a given attribute (Schematron could do that) > > > Cannot be done with XML Schema. > > >>-i'd like that the value of a given attribute exists in my RDBMS > > > Cannot be done with XML Schema, but OASIS CAM can handle this. fine > > Hope that helps-- > thanks -- Cordialement, /// (. .) -----ooO--(_)--Ooo----- | Philippe Poulard | -----------------------
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