On 22/04/2013 23:26, Bert Verhees wrote: > > Verstuurd vanaf mijn iPad > > Op 22 apr. 2013 om 23:19 heeft Thomas Beale <thomas.beale at > oceaninformatics.com> het volgende geschreven: > >> which rules is it breaking? As far as I know, openEHR XML documents validate >> normally against the schemas. > yes, I said it wrong, later in the message I said it better and I forgot to > remove this statement. > > So let me correct myself: > > You cannot represent all Archetype constraints in XML schema, you can of > course validate against the master scheme, but that is not very interesting. > To validate you need to validate against the constraints. That is the > important point of multi level modeling.
that's true if you try to use XSD in its native form. I have been saying the same thing for years. But you can represent archetypes in XML in another way - as a straight object serialisation of an AOM structure. Have a look at the XML output of the current ADL workbench. I didn't create an XSD for that, but it would certainly be possible. The XML format used by the Archetype Editor is of the latter form. > > I discovered some important problems, besides the restriction/extension > structure, which is quite disturbing. You are not allowed to restrict and > extend an derived element at the same time. Just for clarity, A restriction > in deriving in XML Schema is not the same as constraining in ADL. > Read the Priscilla Walmsley book on this, she explains it very well. yes, and she is correct, it's a mess. See my comments to Tim earlier ;-) But there is no danger of openEHR doing this, I think, since we know it won't work effectively. That's why all the > There are ways around this, but it is not very elegant. > > Another very important restriction for using XML Schema, in my opinion, is > that you cannot have two or more elements with the same name but a different > data type. This data type must be in detail the same. XML Schema regards an > Element with a Dv_Text as a different datatype from an Element with a > Dv_CodedText. > > Both elements will be called "items" in an XML schema representing an OpenEhr > data structure, and thus is not allowed having them different details in data > types. This brought Tim Cook to using the GUIDs in the element-names, which > is unworkable in my opinion, and above all, probably unnecessary, because in > RelaxNG this restriction does not exist. > > Other tricks are also possible, for example augmenting element-names during > validation-time, but also that is cumbersome code, and that just for avoiding > the problems of an ivory tower stupid W3C standard? > > So this is indeed an important restriction, which makes the clean use of XML > Schema impossible in OpenEhr-rm, or any other ADL based multi level modeling > system. Dirty use, tricks, ignoring validation errors, etc of course remain > possible. > > There are more restrictions, but less important. For example it is not > possible to support the Dv_Time constraint/pattern hh:??:??, same for > Dv_DateTime. In the Dv_Date is also a problem, but can be worked around by > the "alternative" rule, but on another way then it is meant to use. > > Anyway, after a few weeks I will probably define the OpenEhr RM and all > possible constraints in RelaxNG. > I agree with most of this, but I don't understand the issue - we don't do any of the above anyway. That's why we have ADL, AOM, and object transforms of the AOM... am I missing something? - thomas
