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Data Model WD

From: Jeni Tennison <jeni@jenitennison.com>
Date: Thu, 9 May 2002 06:06:34 -0400 (EDT)
Message-ID: <251473323306.20020509110629@jenitennison.com>
To: public-qt-comments@w3.org
Hi,

Congratuations on the new version of the Data Model WD. On the whole,
it's very clear and well put-together.

I see that you're considering what to do about anonymous types. I
don't think that using the empty sequence as their name will help,
since that's the only method of access to type information, and would
imply that:

<xs:element name="foo">
  <xs:complexType>...</xs:complexType>
</xs:element>

and:

<xs:element name="bar">
  <xs:simpleType>...</xs:simpleType>
</xs:element>

had the same type. But I think that it's important, particularly for
simple types, that they're not just ignored or substituted for
xs:anySimpleType, especially if you consider anonymous simple type
definitions nested within list and union types. For example:

<xs:simpleType name="listOfDatesIn2002">
  <xs:list>
    <xs:simpleType>
      <xs:restriction base="xs:date">
        <xs:minInclusive value="2002-01-01" />
        <xs:maxExclusive value="2003-01-01" />
      </xs:restriction>
    </xs:simpleType>
  </xs:list>
</xs:simpleType>

Say I had:

  <holidays xsi:type="listOfDatesIn2002">
    2002-05-06 2002-06-03
  </holidays>

I can't find the part of the Data Model WD that explains how the
[schema normalized value], which is the string "2002-05-06 2002-06-03"
gets turned into a sequence of AtomicValues, but I assume that's done
by splitting the string at spaces and querying the element's type
definition to get hold of the item type definition somehow (a
particularly complicated process when the item type is a union type).

It would be very unhelpful to have these values interpreted as strings
when they're obviously dates. I think that, at least with anonymous
simple types, it would be more helpful to use the base type of the
anonymous simple type than xs:anySimpleType. Perhaps anonymous complex
types could be treated similarly, although that case is more
complicated because of the different types of derivation that could
occur.


One thing that caused me some confusion on my first read was the way
that the typed value of elements is created (Section 4.2). It appears
that if an element to have a complex type in the schema, then
dm:typed-value returns an error, unless it's declared with the complex
type xs:anyType, in which case dm:typed-value returns its string
value. The more I think about it, the more it makes sense, since
xs:anySimpleType is a subtype of xs:anyType, and for consistency with
the treatment of well-formed documents, but it might be worth a note
or a bit of rephrasing.

By the way, I think that the changes that have been made here have
addressed the issue I raised about whitespace normalization of element
values (Issue-0073: Whitespace normalization of the string-value of
elements with simple content).


There's a small typo in Section 5 Atomic Values. It says:

 "XML Schema simple types can be derived by list. Values
  corresponding to such types are represented by a sequence of atomic
  values whose type is the base type."

Presumably you mean "whose type is the item type". The base type of a
list type (or a union type) is xs:anySimpleType.


The schema from Appendix D isn't valid at the moment, because the
complex type part-type has an xs:attribute within an xs:sequence. It
should be:

  <xs:complexType name="part-type">
    <xs:sequence>
      <xs:element name="mfg" type="xs:string"/>
      <xs:element name="price" type="xs:decimal"/>
    </xs:sequence>
    <xs:attribute name="name" type="part-name"/>
  </xs:complexType>

Even if it were valid, though, the instance document wouldn't be valid
against it. The instance document is:

<?xml version="1.0"?>
<p:part xmlns:p="http://www.example.com/PartSchema"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation = "http://www.example.com/PartSchema
                              http://www.example.com/PartSchema"
        name="NB-401-nutbolt">
  <p:mfg>Acme</p:mfg>
  <p:price>10.50</p:price>
</p:part>

in which the mfg and price elements are in the
http://www.example.com/PartSchema namespace. However, these elements
are declared locally within the schema (in the complex type definition
above), which means, by default, that they should be in no namespace.

You should either change the instance document so that the mfg and
price elements are in no namespace:

<?xml version="1.0"?>
<p:part xmlns:p="http://www.example.com/PartSchema"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation = "http://www.example.com/PartSchema
                              http://www.example.com/PartSchema"
        name="NB-401-nutbolt">
  <mfg>Acme</mfg>
  <price>10.50</price>
</p:part>

or add an elementFormDefault attribute with the value 'qualified' to
the xs:schema element in the schema:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           targetNamespace="http://www.example.com/PartSchema"
           xmlns="http://www.example.com/PartSchema"
           elementFormDefault="qualified">
  ...
</xs:schema>


I hope these comments are helpful.

Cheers,

Jeni
---
Jeni Tennison
http://www.jenitennison.com/
Received on Thursday, 9 May 2002 14:45:16 GMT

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