Cart
|
[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] 'document types' was ...Re: Re: Flexible Schemas
 Nicolas Lehuen wrote: >... You summed it up perfectly : RDDL is for namespaces only. It > won't work for document types. So let's try to solve the problem of document > types together. To the best I can tell an XML 'document type' would refer to that which is defined by a 'document type definition' i.e. a DTD. A 'document type', then, is refered to by the <!DOCTYPE declaration, i.e. a PublicID/SystemID. Catalogs are a terrific way to associate document types with 'stuff'. This, of course, is mostly orthogonal to the namespace of the root element of a document. It is not completely orthogonal because XML 1.0 defines an 'element type' simply as the name of an element (no hierarchy, inheritance etc.). The namespace name of the root, or document, element of a document is of course _part_ of the element's QName. So one can correctly call the 'document _element_ type' the QName of the document element. What is the relationship between the namespace name of the document element and its XML type? To the extent that an element is said to be 'contained' in its namespace, a namespace can be thought of as a container for such types. To be perfectly clear, however, a namespace should not be equated with a type. In my mind one of the most important reasons to propose RDDL in the first place was the fear that namespaces would be incorrectly equated with types. A DTD calls itself a type definition, and by extension a schema can be thought of as a type definition (both are properly collections of type definitions but nonetheless). If a namespace name were to directly reference a schema definition, this improper equation might become a de facto standard, and this is exactly what we wanted to avoid. Regarding the 'problem of document types' either it is completely specified by a DTD, or else we are extending 'document type' into the schema realm (fair enough). Personally I think the issues related to schema composition, especially across schema languages is an interesting one. Some time ago I sketched some thoughts regarding a simple 'schema algebra' http://www.openhealth.org/RDDL/SchemaAlgebra , ( this is not part of the RDDL spec), precisely as an attempt to write down some principles in a logical fashion, and in a way that does not depend on the intracasies of DTDs, XML Schema, RELAXNG etc. I would say, however, that the 'problem', if you define it as: how do we validate an XML document instance whose type definitions can be _derived_ from their namespaces, but without respect to a particular single schema. Firstly I don't know what the term 'valid' means in such situatuions (that would be up to the specifics of the schema language). So in general, the answer to many questions regarding 'document type' fall outside the scope of RDDL. On the other hand, for the reasons I have outlined above, at the very least it is important NOT to directly relate a namespace to a single schema, and this is what RDDL prevents. > > I hope you have understood that I'm OK with RDDL for namespace description > (apart a few critics). But it is only provided that RDDL is not used for > what is not meant, i.e. a substitute for a resource directory for document > types. > That would be an OASIS Catalog. Designed to locate a Document Type Definition given a Public Identifier. Jonathan 
|
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! 
Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|
|||||||||
