Ifc Impl Data Enrichment

IFC Data Enrichment

Data enrichment is the write-side workflow of attaching descriptive data to elements that already exist in a model: property sets, measured quantities, materials, and classification references. Enrichment NEVER changes geometry or spatial structure; it only adds the semantic layer that downstream tools read for quantity take-off, cost, analysis, and compliance.

This skill covers the four enrichment targets, the occurrence-versus-type attachment split, the Pset_ and Qto_ naming rules, and the material set-on-type usage-on-occurrence pattern.

Verified against the IFC 4.3.2 specification (ISO 16739-1:2024) with IFC4 and IFC2x3 deltas noted inline. Applies to IFC2x3, IFC4, IFC4.3.

Quick Reference

The four enrichment targets

Properties and quantities share one attachment machinery: IfcElementQuantity is an IfcQuantitySet, which is an IfcPropertySetDefinition, the same supertype as IfcPropertySet. Both ride IfcRelDefinesByProperties.

The occurrence versus type rule

IfcRelDefinesByProperties carries a WHERE rule NoRelatedTypeObject: its RelatedObjects SET MUST NOT contain an IfcTypeObject.

• ALWAYS attach a property or quantity set to an OCCURRENCE through IfcRelDefinesByProperties.
• ALWAYS attach a property or quantity set to a TYPE through the type's HasPropertySets explicit attribute. NEVER point IfcRelDefinesByProperties at a type object.

HasPropertySets is OPTIONAL SET [1:?] OF IfcPropertySetDefinition, declared directly on IfcTypeObject. A type holds its sets inline; an occurrence holds them through a relationship.

The material set versus usage rule

IfcRelAssociatesMaterial attaches a material to BOTH occurrences and types, but the material object differs:

• The TYPE (IfcWallType, IfcBeamType) ALWAYS takes the bare set: IfcMaterialLayerSet or IfcMaterialProfileSet.
• The OCCURRENCE ALWAYS takes the usage entity: IfcMaterialLayerSetUsage or IfcMaterialProfileSetUsage, which points back at the same bare set via ForLayerSet or ForProfileSet and adds placement. NEVER associate a usage entity with a type.

Naming rules

• Pset_ is RESERVED for the standardised property set library (Pset_WallCommon, Pset_BeamCommon). A custom property set NEVER uses the Pset_ prefix; a Pset_-prefixed custom set collides with the standard library and is silently misread.
• Qto_ is the standardised quantity set prefix (Qto_WallBaseQuantities). This convention is IFC4 and later. IFC2x3 used a BaseQuantities-style convention; ALWAYS check the schema before writing a Qto_ name.

Decision Trees

Which enrichment do I need?

What am I adding to the element?
|
+- A descriptive or design attribute (fire rating, IsExternal,
|  LoadBearing flag, thermal transmittance)
|    -> IfcPropertySet, attached by IfcRelDefinesByProperties
|
+- A measured magnitude derived from geometry (gross area, net
|  volume, count, weight, length)
|    -> IfcElementQuantity, attached by IfcRelDefinesByProperties
|
+- The substance the element is made of
|    -> IfcRelAssociatesMaterial (see the material decision tree)
|
+- A code from an external classification system (Uniclass,
   OmniClass, MasterFormat, ETIM)
     -> IfcRelAssociatesClassification

NEVER store a measured quantity inside an IfcPropertySet, and NEVER store a design property inside an IfcElementQuantity. The two containers are read by different tools.

Occurrence or type?

Is the data the same for every occurrence of this type?
|
+- Yes, it is shared by all occurrences (a wall type's standard
|  layer build-up, a door type's fire rating)
|    -> attach to the TYPE.
|       Properties / quantities -> type.HasPropertySets
|       Material               -> IfcRelAssociatesMaterial with the
|                                  bare set on the type
|
+- No, it varies per placed instance (this specific wall's
   as-built area, this door's tag)
     -> attach to the OCCURRENCE.
        Properties / quantities -> IfcRelDefinesByProperties
        Material               -> IfcRelAssociatesMaterial with the
                                   usage entity on the occurrence

When the same property name exists on both type and occurrence, the OCCURRENCE value wins. Type values are defaults. See ifc-impl-property-extraction for the read-side resolution.

Standard or custom property set?

Does a published Pset_ definition already cover this data?
|
+- Yes -> use the exact standard name (Pset_WallCommon) and the
|         property names and value types it defines. NEVER alter
|         the standard property names.
|
+- No  -> create a custom property set. Its Name NEVER starts with
          Pset_. Use a project or company prefix instead.

Which material structure?

How is the element made of its material(s)?
|
+- One homogeneous substance
|    -> IfcMaterial directly as RelatingMaterial
|
+- Parallel layers (wall, slab, roof, plate)
|    -> IfcMaterialLayerSet on the type,
|       IfcMaterialLayerSetUsage on each occurrence
|
+- An extruded cross-section profile (beam, column, member, pile)
|    -> IfcMaterialProfileSet on the type,
|       IfcMaterialProfileSetUsage on each occurrence
|       (IFC4+ only; this family does not exist in IFC2x3)
|
+- Named parts that are neither layered nor profiled (window
   frame plus glazing, door panel plus hardware)
     -> IfcMaterialConstituentSet (IFC4+; replaces IfcMaterialList)

In IFC2x3 a non-layered composite uses the legacy IfcMaterialList (a bare LIST OF IfcMaterial). ALWAYS use IfcMaterialConstituentSet when authoring IFC4 or IFC4.3.

Patterns

Every snippet uses STEP physical file syntax. $ marks an unset optional attribute. Attribute order is the EXPRESS declared order. Full verified signatures are in references/methods.md; runnable instances are in references/examples.md.

Pattern: attach a property set to an occurrence

#48=IFCPROPERTYSINGLEVALUE('IsExternal',$,IFCBOOLEAN(.T.),$);
#49=IFCPROPERTYSET(
  '1Hkj5pQ9X8x9bq0d6FZ7yA',  /* GlobalId      */
  #5,                        /* OwnerHistory  */
  'Pset_WallCommon',         /* Name          */
  $,                         /* Description   */
  (#48)                      /* HasProperties */
);
#50=IFCRELDEFINESBYPROPERTIES(
  '2k7sB$Qe9X8x9bq0d6FZ7y',  /* GlobalId                   */
  #5, $, $,                  /* OwnerHistory, Name, Desc   */
  (#21,#22),                 /* RelatedObjects : occurrences */
  #49                        /* RelatingPropertyDefinition  */
);

RelatedObjects is a SET [1:?]: one relationship serves many occurrences. NEVER place an IfcWallType in RelatedObjects.

Pattern: attach a property set to a type

A type holds its sets inline through HasPropertySets. No relationship is created.

#46=IFCPROPERTYSET(
  '3mNp7rTf0Y9y0cr1e7GA8z',#5,'Pset_WallCommon',$,(#48));
#20=IFCWALLTYPE(
  '4pQr9sUg1Z0z1ds2f8HB9$',  /* GlobalId             */
  #5, 'Exterior 300mm', $,   /* OwnerHistory,Name,Desc */
  $,                         /* ApplicableOccurrence */
  (#46),                     /* HasPropertySets      */
  $,                         /* RepresentationMaps   */
  $,                         /* Tag                  */
  $,                         /* ElementType          */
  .STANDARD.                 /* PredefinedType       */
);

HasPropertySets is the 6th explicit attribute of any IfcTypeObject subtype. NEVER attach a type's properties with IfcRelDefinesByProperties.

Pattern: attach an element quantity

IfcElementQuantity uses the SAME relationship as a property set.

#70=IFCQUANTITYAREA('NetSideArea',$,$,12.5,$);
#71=IFCELEMENTQUANTITY(
  '5qRs0tVh2$1$2et3g9IC0_',  /* GlobalId            */
  #5, 'Qto_WallBaseQuantities', $,
  $,                         /* MethodOfMeasurement */
  (#70)                      /* Quantities          */
);
#72=IFCRELDEFINESBYPROPERTIES(
  '6rSt1uWi3_2_3fu4h0JD1A',
  #5, $, $,
  (#21),                     /* RelatedObjects             */
  #71                        /* RelatingPropertyDefinition */
);

NEVER store a measured area as an IfcPropertySingleValue inside an IfcPropertySet: quantity take-off tools read IfcElementQuantity only.

Pattern: associate a simple material

#80=IFCMATERIAL('Concrete C30/37',$,'concrete');
#81=IFCRELASSOCIATESMATERIAL(
  '7sTu2vXj4A3A4gv5i1KE2B',
  #5, $, $,
  (#21,#22),                 /* RelatedObjects   */
  #80                        /* RelatingMaterial */
);

RelatingMaterial accepts any IfcMaterialSelect choice. IfcMaterial is the simplest. IfcRelAssociatesMaterial carries a WHERE rule NoVoidElement: a material is NEVER associated with an IfcOpeningElement or an IfcVirtualElement.

Pattern: associate a layered material

The bare set goes on the type; the usage goes on each occurrence.

/* bare set, associated with the IfcWallType */
#90=IFCMATERIALLAYER(#80,0.3,$,'Core',$,'LoadBearing',$);
#91=IFCMATERIALLAYERSET((#90),'EXT-300',$);
#92=IFCRELASSOCIATESMATERIAL(
  '8tUv3wYk5B4B5hw6j2LF3C', #5, $, $, (#20), #91);
/* usage, associated with the IfcWall occurrence */
#93=IFCMATERIALLAYERSETUSAGE(#91,.AXIS2.,.POSITIVE.,-0.15,$);
#94=IFCRELASSOCIATESMATERIAL(
  '9uVw4xZl6C5C6ix7k3MG4D', #5, $, $, (#21), #93);

IfcMaterialLayerSetUsage.ForLayerSet (#91) points back at the same bare set the type uses. NEVER associate an IfcMaterialLayerSetUsage with a type, and NEVER associate a bare IfcMaterialLayerSet with an occurrence when the type is available.

Pattern: associate a classification

#60=IFCCLASSIFICATION($,'2015',$,'Uniclass 2015',$,$,$);
#61=IFCCLASSIFICATIONREFERENCE(
  $,                         /* Location        */
  'EF_25_10',                /* Identification  */
  'Walls',                   /* Name            */
  #60,                       /* ReferencedSource: the IfcClassification */
  $, $                       /* Description, Sort */
);
#62=IFCRELASSOCIATESCLASSIFICATION(
  'AvWx5yAm7D6D7jy8l4NH5E',
  #5, $, $,
  (#21,#22),                 /* RelatedObjects        */
  #61                        /* RelatingClassification */
);

IfcClassification names the SYSTEM; IfcClassificationReference names one CODE inside it. ALWAYS set ReferencedSource so a reader can resolve the code to its system. RelatingClassification accepts either entity.

Pattern: share one definition across many elements

RelatedObjects on every enrichment relationship is a SET [1:?]. ALWAYS list every receiving element in ONE relationship rather than cloning the relationship per element.

#50=IFCRELDEFINESBYPROPERTIES(
  '2k7sB$Qe9X8x9bq0d6FZ7y', #5, $, $,
  (#21,#22,#23,#24),         /* four walls, one relationship */
  #49);

One IfcRelDefinesByProperties per property set, not per element. The same holds for IfcRelAssociatesMaterial and IfcRelAssociatesClassification.

Anti-Patterns

Full detail with the failure mechanism is in references/anti-patterns.md. The ones that matter most:

• Pointing IfcRelDefinesByProperties at a type object. The WHERE rule NoRelatedTypeObject rejects it; types use HasPropertySets.
• Putting an IfcMaterialLayerSetUsage on a type. The usage is occurrence only; the type takes the bare IfcMaterialLayerSet.
• Naming a custom property set with the Pset_ prefix. It collides with the standard library and is misread or ignored.
• Storing a measured quantity inside an IfcPropertySet. Quantity take-off tools read IfcElementQuantity only.
• Cloning one relationship per element instead of listing every element in the single relationship's RelatedObjects SET.
• Setting IfcMaterialLayerSet.TotalThickness by hand. It is a DERIVED attribute computed by the schema.

Reference Links

This skill

• references/methods.md: full positional attribute signatures for every enrichment entity, with supertypes and version notes.
• references/examples.md: verified STEP physical file instances.
• references/anti-patterns.md: failure modes and their root causes.

Related skills

• ifc-syntax-property-sets: building the IfcPropertySet and its IfcProperty value entities.
• ifc-syntax-materials: the structured material entities in full.
• ifc-syntax-classifications: IfcClassification and the external classification systems.
• ifc-impl-property-extraction: the read-side type-versus-occurrence property override resolution.
• ifc-core-relationships: the objectified relationship pattern.

Official sources

• IfcPropertySet: https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcPropertySet.htm
• IfcRelDefinesByProperties: https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcRelDefinesByProperties.htm
• IfcTypeObject: https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcTypeObject.htm
• IfcElementQuantity: https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcElementQuantity.htm
• IfcRelAssociatesMaterial: https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcRelAssociatesMaterial.htm
• IfcRelAssociatesClassification: https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcRelAssociatesClassification.htm