RE: [xml-dev] XQuery types was Re: [xml-dev] Yet another plea for XUpdate...

["Dare Obasanjo" <dareo@microsoft.com>]

We all understand what you are saying but when most of us say "type
system" we aren't talking about your definition of it. In my world,
there are data types and there are constraints which are not mutually
exclusive but not interchangeable either. E.g. the diffence between a
database column called AGE of data type INTEGER and a constraint (CHECK
AGE > 0 ). 

W3C XML Schema and XQuery mix both notions and still try to call it the
same thing which they clearly are not. Given the SQL update statement 

	UPDATE students 
	SET age = ( age - 10); 
     
Although we can tell that the value being assigned to the column is of
the correct "type" at compile time, we cannot tell if this statement
violates the CHECK constraint until runtime when we actually look at the
value in the table. 

Now this is the point I've been trying to make and one can clearly see
that the static type analysis phase can be considered unecessary in
checking if the update is valid since the CHECK constraint covers it and
more. 

Of course, looking at it from a different perspective static types are
constraints as well, they just happen to be evaluated at a different
time. I assume this is the perspective you are taking, non? 

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> -----Original Message-----
> From: Jonathan Borden [mailto:jborden@attbi.com] 
> Sent: Monday, May 06, 2002 8:38 AM
> To: James Clark; Dare Obasanjo
> Cc: xml-dev@lists.xml.org
> Subject: Re: [xml-dev] XQuery types was Re: [xml-dev] Yet 
> another plea for XUpdate...
> 
> 
> James Clark wrote:
> 
> >For example, in his recent book
> > "Types and Programming Languages" Benjamin Pierce (one of the XDuce
> > authors) offers the following definition:
> >
> > "As with many terms shared by large communities, it is difficult to 
> > define "type system" in a way that covers its informal usage by 
> > programming language designers and implementors but is 
> still specific 
> > enough to have any bite.  One plausible definition it this:  A type 
> > system is a tractable syntactic method for proving the absence of 
> > certain kinds of program behaviors by classifying phrases 
> according to 
> > the kinds of values they compute."
> >
> > This is the sense in which the term "type system" is being 
> used when 
> > the XQuery folks talk about the "XQuery type system".
> >
> 
> CLASSIFY: To place objects, words, or situations into 
> categories according to defined criteria for each category.
> 
> As I've said.
> 
> Jonathan
> 
> 
> 
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