# IfcStructuralCurveMember documentation on material profiles refers to non-existent entities and doesn't make sense

**URL:** <https://forums.buildingsmart.org/t/ifcstructuralcurvemember-documentation-on-material-profiles-refers-to-non-existent-entities-and-doesnt-make-sense/3527>\
**Category:** Developers\
**Created:** [April 15, 2021, 12:55am UTC](https://forums.buildingsmart.org/t/ifcstructuralcurvemember-documentation-on-material-profiles-refers-to-non-existent-entities-and-doesnt-make-sense/3527 "2021-04-15T00:55:54Z")\
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**Author:** ![Moult](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/moult/32/196_2.png) [@Moult](https://forums.buildingsmart.org/u/Moult)\
**Post date:** [April 15, 2021, 12:55am UTC](https://forums.buildingsmart.org/t/ifcstructuralcurvemember-documentation-on-material-profiles-refers-to-non-existent-entities-and-doesnt-make-sense/3527/1 "2021-04-15T00:55:54Z")

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Under 7.7.3.10 IfcStructuralCurveMember we find this paragraph:

> The material of direct instances IfcStructuralCurveMember (in contrast to instances of the subtype [IfcStructuralCurveMemberVarying](http://localhost:8001/schema/ifcstructuralanalysisdomain/lexical/ifcstructuralcurvemembervarying.htm)) is defined by [IfcMaterialProfileSetUsage](http://localhost:8001/schema/ifcmaterialresource/lexical/ifcmaterialprofilesetusage.htm) and attached by the _IfcRelAssociatesMaterial.RelatingMaterial_ . It is accessible by the inverse _HasAssociations_ relationship. Composite profile beams can be represented by refering to several [IfcMaterialProfile](http://localhost:8001/schema/ifcmaterialresource/lexical/ifcmaterialprofile.htm)s within the [IfcMaterialProfileSet](http://localhost:8001/schema/ifcmaterialresource/lexical/ifcmaterialprofileset.htm) that is referenced from the [IfcMaterialProfileSetUsage](http://localhost:8001/schema/ifcmaterialresource/lexical/ifcmaterialprofilesetusage.htm). In case of tapered members, the material profile usage subtype _IfcMaterialProfileSetUsageDual_ is used which specifies [IfcMaterialProfileSet](http://localhost:8001/schema/ifcmaterialresource/lexical/ifcmaterialprofileset.htm)s separately at the start and the end of the tapered member.

What is `IfcMaterialProfileSetUsageDual`?

Similarly:

> The material ([IfcMaterial](http://localhost:8001/schema/ifcmaterialresource/lexical/ifcmaterial.htm)) in each [IfcMaterialProfile](http://localhost:8001/schema/ifcmaterialresource/lexical/ifcmaterialprofile.htm)( _Set_ ) is specified minimally by a name which corresponds with an agreed upon standardized structural material designation. An external reference to the source which specifies the material designation should be provided. Alternatively, structural material properties may be provided by means of _IfcMechanicalMaterialProperties_ and _IfcExtendedMaterialProperties_ .

`IfcMechanicalMaterialProperties` and `IfcExtendedMaterialProperties` do not exist.

Maybe this section of the documentation needs to be rewritten? It does not make sense to me.