xml-dev - Re: Basic XMLSchema questions

[Brett McLaughlin <bmclaugh@algx.net>]

Alan Santos wrote:
> 
> > Dah!  I'm asleep today... the reason you need <type> is because you can
> > specify explicit named types:
> >
> > <type name="myType">
> >   <element name="nestedElement" type="string" />
> >   <element name="anotherNestedElement" type="integer" />
> > </type>
> >
> > <element name="myElement" type="myType" />
> >
> > There is no way without the <type> element construct to specify a name
> > for a non-primitive data type without really blowing away any idea of
> > congruity across the element space.  So we have the "type" element.
> >
> > Make sense?
> >
> 
> Yes it does now.
> 
> Syntactically it appears to be legal to simply have <type> on it's own,
> outside of any elements.  Is it simply a stylistic difference to define it
> inside another element?

Nope.  This:

<element name="element1">
  <type>
    <element name="element2" type="string" />
  </type>
</element>

is an implicit element type.  It is used right there and not
referenceable by any other element.

This:

<type name="type1">
  <element name="element2" type="string" />
</type>

is an explicit element type and is referenceable by other elements:

<element name="element1" type="type1" />

This:

<type>
  <element name="element2" type="String" />
</type>

is absolutely useless, as it is not referenceable by any other element,
and is not implicitly assigned to any other element.

Finally, the last permutation:

<element name="element1">
  <type name="type1">
    <element name="element2" type="string" />
  </type>
</element>

is legal, and the type is referenceable by other elements, but is bad
form (IMHO).  If you have a type that will be used multiple times, put
it on its own (explicit type).  If it is only used once, use an implicit
type within the element definition.  Things like this are very
confusing.

-Brett

> 
> thanks,
> alan

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