IFC106 raised when linking bSDD classification to IfcMaterial via IfcExternalReferenceRelationship

[fg55b]

When associating bSDD materials with IfcMaterial instances, as recommended in the bSDD documentation for the IFC4x3_ADD2 & IFC4, the validation raises the IFC106 error. This happens because IfcMaterial does not inherit from IfcRoot, and the current traversal doesn't follow the IfcExternalReferenceRelationship. However, this generates a contradiction between the recommendation and the validation warning.

To solve this specific issue, it seems necessary to either include an exception for the IfcMaterial itself or extend the traversal to ensure these IfcMaterial instances can be linked back to an IfcRoot.

Here is a example of the STEP file and the error:

#171=IFCCOVERING('1OIH5cSlj1YQCpjG2d3l6q',$,'FlowCoating #1','Flow Coating','FlowCoating',$,$,$,.USERDEFINED.); #172=IFCMATERIAL('FlowCoatingMaterial','Flow Coating Material','FlowCoatingMaterial'); #381=IFCRELASSOCIATESMATERIAL('3q60IW2QzDnuWk53gysGGz',$,$,$,(#171),#172); #2421=IFCCLASSIFICATIONREFERENCE('https://identifier.buildingsmart.org/uri/bs-energy/subsea-rigid-pipelines/1.0/class/FlowCoatingMaterial','FlowCoatingMaterial','FlowCoatingMaterial',#2252,'FlowCoatingMaterial',$); #2422=IFCEXTERNALREFERENCERELATIONSHIP('FlowCoatingMaterial','FlowCoatingMaterial',#2421,(#172));

[civilx64]

@fg55b thanks for reporting this. My hunch is that we can resolve this via expanding the list of entity types to traverse e.g. direct relationships or an inverse. We did something similar recently with IfcWellKnownText.

[aothms]

Unfortunately it's not just adding an inverse. The problem here is that we just don't know how these resource level relationships are intended to be used, specifically, which ones count as a reasonable edge to traverse in the context of IFC106 (née IFC105). For IfcPropertyDependencyRelationship we said that this is not an edge in the context of IFC106, both properties need to be used in the context of a rooted property set, but for IfcExternalReferenceRelationship this is probably not the case. So most likely we need to characterise all cases of IfcResourceLevelRelationship.

This patch works

diff --git a/features/steps/steps/model_traversal.py b/features/steps/steps/model_traversal.py
index ada55d6f..7ee9c840 100644
--- a/features/steps/steps/model_traversal.py
+++ b/features/steps/steps/model_traversal.py
@@ -18,6 +18,18 @@ except AttributeError as e:
 
 @gherkin_ifc.step("a traversal over the full model originating from subtypes of .{entity_name}.")
 def step_impl(context, entity_name):
+    def with_subtypes(names):
+        S = ifcopenshell.ifcopenshell_wrapper.schema_by_name(context.model.schema_identifier)
+        def inner(names):
+            for nm in names:
+                yield nm
+                try:
+                    ent = S.declaration_by_name(nm)
+                except RuntimeError:
+                    continue
+                yield from inner({e.name() for e in ent.subtypes()})
+        return set(inner(names))
+
     # @todo fully qualify inverses, because with this many the risk for name clashes becomes significant
     inverses_for_resource_level_rels = {'Relates', 'ApprovedResources', 'IsPointedTo', 'PropertyDependsOn', 'ExternalReferenceForResources',
                                         'IsRelatedWith', 'PropertyForDependance', 'HasApprovals', 'PropertiesForConstraint', 'IsPointer',
@@ -28,7 +40,7 @@ def step_impl(context, entity_name):
     # (inverses_for_resource_level_rels) but traversal stops there. We require both
     # ends of the relationship to point to resources that are used in the context of
     # of a rooted instance regardless of resource-level-relationships connecting them.
-    terminal_entities = {'IfcResourceLevelRelationship'}
+    terminal_entities = with_subtypes({'IfcResourceLevelRelationship'}) - {'IfcExternalReferenceRelationship'}
     schema = schema_by_name(context.model.schema_identifier)
 
     @functools.cache
@@ -84,7 +96,7 @@ def step_impl(context, entity_name):
             return
         visited.add(inst.id())
 
-        if any(inst.is_a(ent) for ent in terminal_entities):
+        if inst.is_a() in terminal_entities:
             return
 
         for attr in names(inst.is_a()):