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> At 02:43 PM 12/4/2002 -0500, Rich Salz wrote:
> >I hope the following is concrete enough.
>
> Yes - thanks for this! This is exactly the kind of concrete example I am
> looking for.
>
> >Imagine the following element:
> ><pi>3.14159265358979323846264338327950288419716939937510582097494459230781640628620899
> ></pi>
> >
> >(See http://www.joyofpi.com/pi.htm for details).
> >
> >Suppose you are building a web services front-end to Macsyma (or
> >Mathematica). You might be tempted to add this attribute (assuming the
> >"obvious" xmlns declarations)
> > xsi:type=xsd:float
> >
> >The problem is, that if you use something like DevStudio.Net and its
> >wizards, you've guaranteed to have lost precision. That's a shame,
> >because the math tool has effectively infinite precision, but my
> >XML/WS/XSD tool artificially limits itself to IEEE floats because it
> >thinks it's doing me a favor by making it trivial to generalize object
> >serialization through XML.
>
> Well, there's a problem you will encounter earlier. Float and double are
> restricted to 32 and 64 bits respectively:
>
> >3.2.4 float
> >
> > [Definition:] float corresponds to the IEEE single-precision 32-bit
> > floating point type [IEEE 754-1985].
> >
> >3.2.5 double
> >
> > [Definition:] The double datatype corresponds to IEEE
> > double-precision 64-bit floating point type [IEEE 754-1985].
>
> That means that your document would not validate if you used these
> datatypes.
This does not follow from what you quoted. Many IEEE systems will accept
literals expressed in arbitrary local format, and convert to value space
accordingly. I think it is broken for WXST to say that providing extra
precision is a validation error. It is much less broken to say that the extra
precision is discarded. But then you're right back to the value-space
problems Rich brought up.
> Of course, if you *did* use these datatypes, then a wizard could
> make safe assumptions about precision,
A wizard could also make such safe assumptions given a simple set of modular,
generic constraints that complement rather than complicate the lexical basis.
> but your example precludes use of
> these types.
>
> There *is* a datatype that I could use to represent Pi to ten thousand
> digits (or one million if I bought the book):
>
> >3.2.3 decimal
> >
> > [Definition:] decimal represents arbitrary precision decimal
> > numbers.
>
> If the document uses this datatype, then the Wizards had better be aware of
> what the phrase "arbitrary precision" means.
So do tell. What *does* that mean? I assume it means "limited by machine
resource constraints"? I don't see that such a vagary provides any interop
benefits whatsoever.
> Using the datatype is a clear
> warning to applications. Without the datatype, an application might
> encounter decimals of very different sizes, but not be aware that arbitrary
> precision numbers might arise until they encounter the first REALLLY BIG
> number.
I don't understand the gain you see here. I'm thinking as someone who writes
software, and I'm not sure how the xsd:decimal has helped me here. Certainly,
since I want to stay paid by my client, I'm not going to allocate all
available memory for every number that is marked as xsd:decimal. How I would
actually code it probably depends on whether I were working in a static or
dynamic library. In the former case, I guess the need for static type
declations is some weak justification, but I would hope that my language
provides enough generic escapes to write things more efficiently, anyway. In
the case of dynamic languages, I see no reason why I wouldn't allocate
structures for numbers as I come across them, adjusting for size as I need to.
So I am completely missing what that data type buys me.
> Of course, you can write schemas that use decimals of fixed precision too.
> In either case, the schema is explicit about the kinds of data applications
> should be prepared to handle.
>
> So isn't the use of datatypes more helpful than harmful in this case?
No. In fact, your examples demonstrate just one more bit of poison introduced
by careless use of data types: false promises.
--
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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