Strong Typing in SGML and XML

Tim Bray tbray at
Tue May 6 19:24:11 BST 1997

At 09:44 AM 5/6/97 GMT, Peter Murray-Rust wrote:

>> 3. The syntax for dates and so on should match some ISO standard,
>>    but I haven't found which one yet.
>Do you mean you there are several and you haven't decided between them?
>I thought that people had converged on a single one (I can't remember
>the number, it's something like 8601).

I mean I spent half an hour poking around the Web and didn't come
up with anything right away.  If someone will send me a pointer to
the standard syntax, I'll put it in the draft.

>I don't find SQLSIZE 'obvious'

OK, all of the types but one need a single parameter; each parameter
is numeric, except for DATE, which is a boolean for timezone
existence.  I didn't want to make up different attributes for each one.
Yes, it's hopelessly overloaded.  Maybe it should just be called
XML-SQLPARAM.  It is *not* the case that there is a single concept
in SQL to which all these parameters map.

>In box 2 you have XML-MIN - I assume this is a typo.


>I found SIZE, MIN and MAX, very confusing.  I *think* that the text is 
>correct, but it's very easy to get lost.  Are we stuck with these?

Not stuck; this is the first ever draft.  Improvements welcome.

>4.5  Presumably SQLMIN<=SQLMAX? etc...


>4.6 Reference to SQL SCALE was unclear.  Is there a requirement for SQLSCALE
>as well or does this simply need rewriting.

Scale of a decimal fraction is the number of digits to the right of
the decimal point.

>4.7 I am not happy without exponential notation.  For example do we 
>really have to represent Avogadro's number (6.023E+23) as
>602300000000000000000000?  Surely we can use IEEE notation?

Yes, this has to be supported.  Somebody else pointed that out too.

>Is equality defined/definable for floating point?

Yes, because in the real world, there are no real numbers [sorry,
math joke] - what I mean is that floating point numbers exist either
as fixed-size binary objects in computer storage, or as strings of
digits, decimal points, and exponents, also in storage.  Either
way, equality tests are meaningful.  Given good implementations of
the IEEE rules, they are even useful.


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