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Conflict between BBX001 and MPD001 when using BoundingBox in IfcMappedItem #510

@fg55b

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@fg55b

Greetings everyone!

I encountered a potential conflict between rules BBX001 and MPD001 when validating IfcShapeRepresentations containing IfcMappedItems. This issue was found while using a 'BoundingBox' representation as the source for an IfcMappedItem. The details of the failing instance structure are illustrated in this diagram.

As shown in the diagram, the product has a representation with RepresentationIdentifier set to 'Box'. However, since this shape representation references an IfcMappedItem in the Items attribute, its RepresentationType is expected to be 'MappedRepresentation', as defined in the formal proposition CorrectItemsForType (function IfcShapeRepresentationTypes).

Rule BBX001 stipulates that if the RepresentationIdentifier is 'Box', the RepresentationType must be 'BoundingBox'. Conversely, according to MPD001, the validator expects the RepresentationIdentifier to correspond to that of the mapped representation, which is 'Box' in this case. Therefore, a contradiction is unavoidable for this specific configuration.

Are Bounding Boxes intended to be valid targets for IfcMappedItem? If so, should BBX001 be updated to accept 'MappedRepresentation' as a valid RepresentationType when the RepresentationIdentifier is 'Box'?

Additional Note:
Regarding rule MPD001, I noticed that the 'expected' and 'observed' values in the validation log appear to be swapped, as shown in the diagram.

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