Restrictions on types

[Kim Lokøy]

I have the following class hierarchy / type hierarchy:

A
a
b
c

The xml schema is something like this:

<complexType name="A">
<sequence>
<element minOccurs="1" name="parent" type="A"/>
</sequence>
</complexType>
<complexType name="a">
<complexContent>
<extension base="A"/>
</complexContent>
</complexType>
<complexType name="b">
<complexContent>
<extension base="A"/>
</complexContent>
</complexType>
<complexType name="c">
<complexContent>
<extension base="A"/>
</complexContent>
</complexType>
A is the superclass of a, b and c. A defines a parent that is a pointer
to an instance of one of its subclasses. But there are some
restrictions of what parent can be in the different subclasses. The
following rules apply:

a.parent can be instance of a
b.parent can be instance of a or b
c.parent can be instance of a or b

Is there a way I can capture this in XML Schema? Is there a way to use
enumeration on types?

Thanks
Kim

[Henry S. Thompson]

Kim Lokøy writes:

I have the following class hierarchy / type hierarchy:

A
a
b
c

The xml schema is something like this:

<complexType name="A">
<sequence>
<element minOccurs="1" name="parent" type="A"/>
</sequence>
</complexType>
[Minor note -- this accepts only infinite documents -- minOccurs
maybe should be 0 ?]
<complexType name="a">
<complexContent>
<extension base="A"/>
</complexContent>
</complexType>
<complexType name="b">
<complexContent>
<extension base="A"/>
</complexContent>
</complexType>
<complexType name="c">
<complexContent>
<extension base="A"/>
</complexContent>
</complexType>
A is the superclass of a, b and c. A defines a parent that is a
pointer to an instance of one of its subclasses. But there are some
restrictions of what parent can be in the different subclasses. The
following rules apply:

a.parent can be instance of a
b.parent can be instance of a or b
c.parent can be instance of a or b

Is there a way I can capture this in XML Schema? Is there a way to
use enumeration on types?

I _think_ this would follow if you used restriction instead of
extension, but I can't be sure because I'm not clear what documents
you have in mind -- Is something such as

<root xsi:type='a'>
<parent xsi:type='b'>
<parent xsi:type='c'/>
</parent>
</root>

what you had in mind as OK, but

<root xsi:type='a'>
<parent xsi:type='b'>
<parent xsi:type='a'/>
</parent>
</root>

not OK?

ht
--
Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
Half-time member of W3C Team
2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
Fax: [phone], e-mail: [e-mail]
URL: http://www.ltg.ed.ac.uk/~ht/
[mail really from me _always_ has this .sig -- mail without it is forged spam]