Cart
|
[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XML-with-datatypes -- a sketch proposal
 Vladimir Gapeyev wrote: > > On Thu, 13 Oct 2005, Mail wrote: > >> However, I don't think it is really that hard to extend XML further to >> make it strong typed. XML was initially designed without Namespace, >> and it is now patched with namespace and everyone is happy to accept it. I second Amelia's laughter on this point. > I think you idea of introducing datatypes as an add-on similar to > namespaces (or xml:ID) can be carried out by adding a bit more semantics > to the xsi:type attribute, and moving it from WXS to XML Core. An > important thing, I believe, would be to provide a framework for defining > datatype identifiers and declaring them on document nodes, but to leave > actual definitions of the datatype identifiers, lexical and semantic > spaces, outside the specification and in the hands of the users and > organized user groups. There's a complexity cost to any addition to the core. Even if the proposal were all advantage and no disadvantage, it still might well not be worth it. So far I don't see a compelling benefit to doing this. > E.g. here is an example of a document that conforms to the hypothetical > XML-with-datatypes: > > <?xml version='1.0'?> > <order xmldt:currency="my:banks:currency:format" > xmldt:date="http://www.w3.org/2001/XMLSchema/date" > xmldt:text="http://www.standardsbody.org/xmld/1.0/pcdata" This document is namespace malformed. You need to declare the xmldt prefix. > - The document above is XML-conformant. But not namespace conformant > - The xmldt attribute is reserved by the "Datatype definitions for XML" > specification. It's not an attribute. It's a namespace prefix. Reserving these is *BAD*. URIs matter. Prefixes don't. That's at the heart of namespaces. That xml: is an exception is grandfathered in, and this causes major problems for implementations. > - In the root element, xmldt binds datatype URIs to short names. The > URIs, as well as lexical and semantic spaces for values of the > corresponding datatypes, are defined by user groups, or just agreed upon > between two > developers. Why does this need to go into the core then? Why do such agreements need a separate lexical space/ What's wrong with GIs? > - On elements that carry datatype values, xmldt declares the datatype, > by referring to a short name. names would need to be prefixed and namespace qualified. > - A conformant XML processor checks that all referenced types are > declared, and passes information about the type to the application > whenever a typed node is encountered. Why would I want to do this? Most of the time I don't validate already. > Notes / Questions: > > - It is possible for a conformant processor to pass the type information > to the application by returning a parsed semantic value instead its raw > lexical text -- according to the conventions established between the > processor and the application. Not in any current API; and probably not in any API if the type system is extensible. I once tried to design a new version of SAX that could do this just with schema types. I couldn't figure out how. > - This offers datatypes only for elements, but not for attributes. Is > this a big disadvantage? Only in so far as types matter at all. > - I suspect that the effect of this proposal can be achieved today via > WXS xsi:type or notations, but this would still require one to use > schemas, even in a project where the requirement is just to know > datatypes at the leaves, but process the tree structure dynamically. Is > such a requirement uncommon? You can use xsi:type without pulling in a schema. -- Elliotte Rusty Harold elharo@m... XML in a Nutshell 3rd Edition Just Published! http://www.cafeconleche.org/books/xian3/ http://www.amazon.com/exec/obidos/ISBN=0596007647/cafeaulaitA/ref=nosim 
|
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
|
|||||||||
