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Rick Jelliffe:
> I think we need to draw the line between different kinds of "typelessness".
>
> There is
> * late binding (where the information needed for typing is only available
> at the last minute)
In my construction, I think this is the preference of most bohemians.
> * reflection (where the object carries its type information around)
Gah. Silly Java terminology ;-)
Can we just call this "intrinsic type". i.e. something that approximates
English usage?
> * casting (where the language or some context forces a thing to be
> treated a certain type)
Hmm. This to me is just late binding with language-specific details.
> * generic operations (where, rather than a thing having no type, it
> is deemed to have some very generic operations, such as equality testing
> only)
Yes. Yes. Yes. I think this is an *essential* conformance level for XML
data typing. If you put this generic power into a Turing complete language
such as XSLT, then you end up with all the power of static typing, yet much
more flexibility.
> * dynamic typing, where a value is looked at, and the type is selected from
> it according to lexical hints
Yes. This should be every bit as important as static typing. Also, the hints
should also be able to come from environment.
> * typelessness, at an extreme where an operation occurs without any
> checking on some kind of memory location or a pointer.
>
> The occurrences of these in XML might be
> * late binding, such as in XML Schemas when you may access base
> types very late
Unless XPath invokes the type without your explicitly telling it to do so.
Also, it seems to me that using a Schema is very early binding (i.e. during
validation, which is considered a phase in parsing). Why do you say it is
late?
> * reflection, such as using xsi:type to figure out the type
I don't understand this. I would say that reflection is more a matter of
using type() in XPath 2.0. xsi-:type is a type declaration, not a reflection
operator.
> * casting, such as where a query treats some text as a particular type
> * generic operations, pretty much what XML is without XML Schemas,
> wander around trees and look a strings.
Well not really. Fundamental specs such as XPath don't provide adequate tools
for generic processing. We've discussed this on XML-DEV before, and have an
idea what such a module might look like. Along comes XPath 2.0 which dumps 10
tons of cruft for static typing, and still not a peep for generic processing,
which, as you say is "XML is without XML Schemas". Doesn't that seem queer?
> * dynamic typing, such as the = operation in XSLT
Which is what I say we need more of, on the same modular basis as the need for
data typing.
That's all.
> I don't really see any typelessness at work in XML: it seems to be a property
> of languages rather than data.
Oh no. It is certainly a property of data.
--
Uche Ogbuji Fourthought, Inc.
http://uche.ogbuji.net http://4Suite.org http://fourthought.com
Tour of 4Suite - http://www.xml.com/pub/a/2002/10/16/py-xml.html
Proper XML Output in Python - http://www.xml.com/pub/a/2002/11/13/py-xml.html
RSS for Python - http://www-106.ibm.com/developerworks/webservices/library/ws-p
yth11.html
Debug XSLT on the fly - http://www-106.ibm.com/developerworks/xml/library/x-deb
ugxs.html
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