clarification on WMS 1.3.0 BoundingBox

[Kralidis,Tom [Ontario]]

Hi: for WMS 1.3.0, (OGC 06-042) Section 7.2.4.6.8 states:

'WMS service metadata shall declare one or more bounding boxes (as
defined in 6.7.4) for each Layer.  A Bounding Box metadata element may
either be stated explicitly or may be inherited from a parent Layer....'

However, in http://schemas.opengis.net/wms/1.3.0/capabilities_1_3_0.xsd,
wms:Layer allows 0..* of wms:BoundingBox.

Which one is definitive?  The body of the document?  If yes, do we need
a change request?

Thanks

..Tom

================================
Tom Kralidis
Senior Systems Scientist
Geospatial Coordination Office
Chief Information Officer Branch
Environment Canada
Tel: [phone]
http://www.ec.gc.ca/
 
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[Keith Pomakis]

Kralidis,Tom [Ontario] wrote:

> Hi: for WMS 1.3.0, (OGC 06-042) Section 7.2.4.6.8 states:
>
> 'WMS service metadata shall declare one or more bounding boxes (as
> defined in 6.7.4) for each Layer.  A Bounding Box metadata element may
> either be stated explicitly or may be inherited from a parent Layer....'
>
> However, in http://schemas.opengis.net/wms/1.3.0/capabilities_1_3_0.xsd,
> wms:Layer allows 0..* of wms:BoundingBox.
>
> Which one is definitive?  The body of the document?  If yes, do we need
> a change request?

In my opinion, an XSD schema document need not (and in general cannot)
capture all of the nuances of what the specification defines as a legal
XML document.  In this particular situation the specification states
that each layer MUST have a bounding box, but that that bounding box
MAY be inherited from a parent layer.  However, the layer inheritance
rules aren't captured by the XSD schema document.  The schema COULD be
made more complicated by distinguishing between top-level layers (which
would have bounding box multiplicity of [1..*]) and non-top-level layers
(which would have bounding box multiplicity of [0..*]).  This would
allow a validator to check a little bit more.  But it still wouldn't
be a complete validation because interitance rules like "the bounding
boxes of a layer must lie spatially within the bounding boxes of it
ancestor layers" still aren't captured by the schema.

In summary, I think it's important to recognize the limitations on the
validation power of XSD schema documents and to not waste too much energy
(and add too much complication) trying to combat this.

---
Keith Pomakis <pomakis@...>
Senior Software Developer, CubeWerx Inc.
15 rue Gamelin, Gatineau, Québec J8Y 3B5
Phone: [phone] x202, FAX: [phone]
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