xml-dev - element order restrictions?

[glen.albert@autodesk.com]

I've run into a roadblock on a schema I'm developing. I'm not sure if it's a
problem with my implementation or if it's an issue with the validator I'm
using.

I have a CoordGeom (Coordinate Geometry) element to define Civil Engineering
and Surveying features such as road alignments or property boundaries. This
element is an ordered collection of mixed element types (lines, curves and
spirals). In the instance document, the elements need to appear in order as
the geometric feature is traversed. Stripped down to its basic form the
CoordGeom definition is as follows;

	<element name="CoordGeom">
		<complexType>
				<element ref="Line" minOccurs="0"
maxOccurs="unbounded"/>
				<element ref="Curve" minOccurs="0"
maxOccurs="unbounded"/>
				<element ref="Spiral" minOccurs="0"
maxOccurs="unbounded"/>
		</complexType>
	</element>

An instance may appear as follows.

	<CoordGeom>
		<Line>
			<Start>5632.87775300 3944.16966200</Start>
			<End>5632.87775300 4044.16966200</End>
		</Line>
		<Line>
			<Start>5632.87775300 4044.16966200</Start>
			<End>5782.87775300 4044.16966200</End>
		</Line>
		<Curve>
			<Start>5782.87775300 4044.16966200</Start>
			<End>5832.87775300 3994.16966200</End>
			<Center>5782.87775300 3994.16966200</Center>
		</Curve>
		<Line>
			<Start>5832.87775300 3994.16966200</Start>
			<End>5832.87775300 3944.16966200</End>
		</Line>
	</CoordGeom>

Is this allowed or do I need to take a different approach? The validator
that I'm using expects all Line elements to occur before a Curve element is
encountered. I've tried various approaches, but haven't been able to come up
with a simple solution.


Thanks,
Glen Albert


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