Re: [xml-dev] XML schema type question

["Jeff Greif" <jgreif@alumni.princeton.edu>]

Thanks, Jeni.  This seems a good approach.  Your patient and thoughtful
responses on this list to various practical and theoretical questions are
greatly appreciated

I think one of the reasons this kind of thing is difficult is that there is
only a way to distinguish between the type of an element (including its
attributes and outside-the-angle-brackets content) and the type of the
content alone.  If this were possible, then you would be able to say that in
general, the element foo supported attributes a and b, and allowed anyType
for content, and a particular instance element named foo had content of type
xsd:boolean.  So along with xsi:type it would be nice to have
xsi:content-type.

What I wound up doing is cruder -- I used an no-attribute intermediate
element, as in
  <complexType name="fooType">
    <sequence>
       <element name="value" type="anyType"/>
    </sequence>
    <attribute name="a" ...>
    <attribute name="b" ...>
  </complexType>

  <element name="foo" type="fooType">

and in the instance
   <foo a="x" b="y"><value xsi:type="xsd:boolean">true</value></foo>
   <foo a="xx" b="yy">
       <value xsi:type="someComplexType>
           <someComplexElt>...</someComplexElt>
       </value>
   </foo>

Jeff


----- Original Message -----
From: "Jeni Tennison" <jeni@jenitennison.com>
To: "Jeff Greif" <jgreif@alumni.princeton.edu>
Cc: <xml-dev@lists.xml.org>
Sent: Friday, September 27, 2002 2:11 AM
Subject: Re: [xml-dev] XML schema type question


> Hi Jeff,
>
> > I've seen the XML Schema Type Library's "text" type, supporting
> > arbitrary mixed content. I have been unable to figure out how to
> > define a complex type whose contents are any simple type value or
> > any single element, but not a mixture, where an element of this
> > special type has a certain set of attributes That is, I'm trying to
> > define
> >
> > <element name="foo">
> > <complexType >
> >    ??? some kind of restriction of anyType with either simple or complex
content
> >    <restriction base="anyType">
> >      ???
> >      <attribute name="a" ...>
> >      <attribute name="b" ...>
> >    </restriction>
> >   ???
> > </complexType>
> > </element>
> >
> > so I can say in instance docs
> >
> > <fooList>
> >    <foo a="x" b="y" xsi:type="xsd:boolean">true</foo>
> >    <foo a="xx" b="yy" xsi:type="SomeComplexType">
> >       <someComplexType>...</someComplexType>
> >    </foo>
> >     ...
> > </fooList>
>
> I don't think that you can do precisely what you want, particularly
> because if you do xsi:type="xs:boolean" then you're saying "the foo
> element is (the simple type) xs:boolean", which isn't true because it
> has attributes.
>
> What you can do, I think, is as follows. Start off with a general
> complex type for your element which is *mixed* (allows both text and
> element content) and has the attributes that you want to be common to
> all your foo elements:
>
> <xs:element name="foo" type="_fooType" />
>
> <xs:complexType name="_fooType" abstract="true" mixed="true">
>   <xs:attribute name="a" type="xs:string" />
>   <xs:attribute name="b" type="xs:string" />
> </xs:complexType>
>
> You can then derive, by restriction, from that type in two ways.
> First, you can derive types that have complex content and *aren't*
> mixed (don't have textual content):
>
> <xs:complexType name="_fooComplexContentType" abstract="true">
>   <xs:complexContent>
>     <xs:restriction base="_fooType" />
>   </xs:complexContent>
> </xs:complexType>
>
> Second, you can derive types that have simple content of a type of
> your choice:
>
> <xs:complexType name="_fooSimpleContentType" abstract="true">
>   <xs:simpleContent>
>     <xs:restriction base="_fooType">
>       <xs:simpleType>
>         <xs:restriction base="_fooSimpleType" />
>       </xs:simpleType>
>     </xs:restriction>
>   </xs:simpleContent>
> </xs:complexType>
>
> <xs:simpleType name="_fooSimpleType">
>   ...
> </xs:simpleType>
>
> Finally, you can derive the concrete types that you want to use in
> your instance from these types, by extension (to add element content
> to the empty _fooComplexContentType) or restriction (to specify the
> allowed values of the _fooSimpleType).
>
> (It's *so* much easier in RELAX NG...)
>
> Cheers,
>
> Jeni
>
> ---
> Jeni Tennison
> http://www.jenitennison.com/
>
>
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