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Re: Data Model WD

From: Jeni Tennison <jeni@jenitennison.com>
Date: Thu, 23 May 2002 11:05:01 +0100
Message-ID: <121327954723.20020523110501@jenitennison.com>
To: Marton Nagy <MARTON.NAGY@saic.com>
CC: public-qt-comments@w3.org
Hi Marton,

Thanks for getting back to me about my comments. Just to pick up on
one of them.

> You are right. At the time of the publication we took a very simple
> approach for handling restrictions of simple types: we just used
> xs:anySimpleType to label those. Since then, we have revisited this
> decision and will likely do what you suggest: label these
> restrictions with the name of the base type (if that has a name), or
> walk up the type hierarchy till we find one that is named and use
> that.
> Also note that the data model already handles list types. If your
> example would just be a list of dates (rather than a list of
> restrictions of dates), the atomic values in the sequence would be
> properly labeled with xs:date. So once we fix the algorithm of
> obtaining the type name of a subtype the whole example will be
> handled properly.

That sounds great. As you revisit this, here's another example (which
I had posted to XML-Dev) that demonstrates a problem with lists of
union types:

Say you have:

<xs:simpleType name="commandType">
  <xs:restriction base="xs:token">
    <xs:enumeration value="moveto" />
    <xs:enumeration value="lineto" />

<xs:simpleType name="commandOrCoordType">
  <xs:union memberTypes="commandType xs:integer" />

Imagine a commandOrCoord attribute with type commandOrCoordType:


In the PSVI, the commandOrCoord attribute information item has a
schema normalized value of "moveto", a type definition of
commandOrCoordType and a member type definition of commandType.

In the XQuery/XPath 2.0 data model, the attribute node has a type of
commandOrCoordType and a typed value with the value 'moveto' and the
type commandType. That's all fine, because you can get the type of the
single value from the member type definition of the PSVI.

Now consider:

<xs:simpleType name="pathType">
  <xs:list itemType="commandOrCoordType" />

and a path attribute with the type pathType:

  path="moveto 100 300
        lineto 200 400 300 300"

The PSVI contains a path attribute information item with a schema
normalized value of "moveto 100 300 lineto 200 400 300 300", a type
definition of pathType and no member type definition.

To satisfy its requirement that atomic values are always of atomic
types, the XQuery/XPath 2.0 data model needs to translate this into an
attribute node whose typed value is the sequence ('moveto', 100, 300,
'lineto', 200, 400, 300, 300), with the 1st and 4th items being atomic
values of the type commandType and the rest of the items being atomic
values of the type xs:integer.

I don't think that the current data model WD describes how you get
from the schema normalized value and the type definition of pathType
to the sequence of commandTypes and integers. I believe that it
requires a separate invocation of the schema validator to work out the
member type of the items in the sequence, since the information about
the types of individual values isn't present in the PSVI.



Jeni Tennison
Received on Thursday, 23 May 2002 06:10:34 UTC

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