Lists Home |
Date Index |
> 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:
> >(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
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
> 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
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
Debug XSLT on the fly - http://www-106.ibm.com/developerworks/xml/library/x-deb