XSD File Issues

[Eddie-Hartman]

I also ran into this issue: #987 (comment) and then changed to unbound/grabbed the latest dev version.

@aothms Since you asked, using the latest dev version IFC4X3_DEV_f498d15 file, I tried generating C# classes using https://github.com/mganss/XmlSchemaClassGenerator/

I've had success with this in the past with files like the Common Alerting Protocol: https://www.fema.gov/emergency-managers/practitioners/integrated-public-alert-warning-system/technology-developers/common-alerting-protocol

And here was the result:

Generated Type 'https://standards.buildingsmart.org/IFC/RELEASE/IFC4/3/DEV/f498d15:IfcBinary' is not declared, or is not a simple type.
Generated Invalid content type derivation by restriction. If the derived content type is Empty, then the base content type should also be Empty or Mixed with Emptiable particle according to rule 5.3 of Schema Component Constraint: Derivation Valid (Restriction, Complex).
Generated Type 'https://standards.buildingsmart.org/IFC/RELEASE/IFC4/3/DEV/f498d15:IfcCompoundPlaneAngleMeasure' is not declared, or is not a simple type.
Generated Type 'https://standards.buildingsmart.org/IFC/RELEASE/IFC4/3/DEV/f498d15:IfcCompoundPlaneAngleMeasure' is not declared, or is not a simple type.
Generated Invalid particle derivation by restriction - 'Derived element 'https://standards.buildingsmart.org/IFC/RELEASE/IFC4/3/DEV/f498d15:HasSubContexts' is not a valid restriction of base element 'https://standards.buildingsmart.org/IFC/RELEASE/IFC4/3/DEV/f498d15:WorldCoordinateSystem' according to Elt:Elt -- NameAndTypeOK.'.
Generated Invalid particle derivation by restriction - 'Derived element 'https://standards.buildingsmart.org/IFC/RELEASE/IFC4/3/DEV/f498d15:HasProperties' is not a valid restriction of base element 'https://standards.buildingsmart.org/IFC/RELEASE/IFC4/3/DEV/f498d15:ParentProfile' according to Elt:Elt -- NameAndTypeOK.'.
Generated Invalid particle derivation by restriction - 'The derived element https://standards.buildingsmart.org/IFC/RELEASE/IFC4/3/DEV/f498d15:StyledByItem at (5315, 7) is not a valid restriction of the base sequence particle at (0, 0) according to Elt:All/Choice/Sequence -- RecurseAsIfGroup.'.
Generated Invalid particle derivation by restriction.

I'm generally looking to make C# classes from the XSD file since there isn't as much support for EXPRESS for this purpose and I've had success with XSD in the past.

I'd like to see some of these issues resolved or some guidance so I can create the C# class library.

[aothms]

I think first thing to try is whether you have more luck with the previous edition:

https://standards.buildingsmart.org/IFC/RELEASE/IFC4/ADD2_TC1/XML/IFC4.xsd

If so, we can work our way towards figuring out the differences.

If not, we'll have to figure out a plan going forward. Good news is that there is likely going to be an IFC4.4 in some time so maybe we can make this a budget item there. Until that time, unless somebody is interested in taking the lead to resolve this (you?) or we find budget somewhere, we likely won't see much progress.

since there isn't as much support for EXPRESS for this purpose and I've had success with XSD in the past.

I want to keep reiterating this. Step physical file (iso 10303-21) constitutes 99% of the ifc file exchanges (if not more). Please don't consider XML (iso 10303-28) as an equivalent choice for encoding IFC data. ifc-xml might have some niche uses (property set templates in FM for example) but outside of these niches ifcxml is pretty much non-existent.

[Eddie-Hartman]

@aothms thanks for the reply. I'm at an openBIM conference in the US and am just learning about this this week and will discuss with some buildingSmart employees here. I'm providing this context to be clear that I'm looking at all of this for the very first time as of this week and just trying to understand things.

Just to clarify my intent here, I wanted to take the XSD file to generate some C# classes to help me wrap my head around the specification since it's so large. Then, I'd be able to use those same classes to perform analysis on the files/models themselves. I understand that the XML files themselves are not what is commonly used in exchanges.

I'm approaching this more from a research perspective than having an outright solution and end goal in mind. Is there a better place for me to land in terms of software "getting started" or sdks? I've seen some other libraries and things floating around such as XBIM https://github.com/xbimteam (not an endorsement), but I'd like to better understand the underlying file format itself and the schema is just too massive to work with in any manual fashion or manual review. That's why I was hoping to start with the XSD to C# which would outline the structure more clearly (to me at least).

Just wanted to openly communicate things as I see them to support the open ecosystem. Thanks.

[aothms]

Just some random remarks then:

• The schema can be pretty uninformative in certain aspects. Things like: IfcProduct -> ... -> IfcRepresentationItem are very generally expressed at the schema level and only come to life when looking at how the data is typically used.
• For that matter CH4 of spec can be rather informative, if you familiarize yourself with how to read them https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/concepts/content.html They are like a meta-configuration on top of the schema
• The implementation guide (although dated and from before the infra additions) might be useful for some introductory reading https://standards.buildingsmart.org/documents/Implementation/IFC2x_Model_Implementation_Guide_V2-0b.pdf
• The schema language express (iso 10303-11) is really powerful, but in essence also easy to parse. If you're looking for a way to analyse the schema outside of existing toolkits you could take the grammar and parse the schema yourself.
• The spec is huge, but essentially a collection of (infamously non-modular) islands, like (a) representation items (b) built item taxonomy (c) objectified relationships (d) practically unused definitions (e) ...