Mattias Bengtsson
If so, how do you specify where foreign namespaces are legal? If the top-level DTD specifies -- and thus needs to know, in advance, the details about -- the sub-namespaces, then what's the point of namespaces at all?
This is exactly what i'm also having trouble understanding. Need to read more!
I'm confused.
So am i. :)
Well - I just found some links. A schema can contain import statements, basically #include'ing other schemas: http://lists.xml.org/archives/xml-dev/200211/msg00880.html For DTD's, I think you'd have to write the DTD to use the prefix (I forget the proper name for it) and the local name - but I've lost the link that said so. So for both Schema and DTD validation, you'd need to know in advance all the tags you'd like to use, but Schema lets you more easily reuse 'chunks' of the document definition (or XML grammar). Stray thought: I'm currently working on a storage for various data types. Due to the variety, I'm considering XML rather than SQL, and it occurs to me that SQL relations are product types, while XML defines an algebraic data type. E.g., we can straightforwardly translate: <!ELEMENT element-name (child-name)> => data ElementName = ElementName ChildName <!ELEMENT element-name (child1,child2)> => data ElementName = ElementName Child1 Child2 <!ELEMENT element-name (child?)> => data ElementName = ElementName (Maybe Child) <!ELEMENT element-name (child*)> => data ElementName = ElementName [Child] <!ELEMENT element-name (child1|child2)> => data ElementName = ElementName1 Child1 | ElementName2 Child2 Well - presumably, something like that is exactly what you do to produce verifiable XML, right? In my mind, the 'algebraic' data types have always been a practical thing, but I suppose there is a formal framework where both Haskell data types and XML are unified as examples of 'algebraically complete' systems? Basica stuff I guess, it just never occurred to me to combine the terms 'universal algebra' and 'XML' before. :-) -k -- If I haven't seen further, it is by standing in the footprints of giants