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Skillsifc-impl-data-enrichment

ifc-impl-data-enrichment

Data & analytics

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Updated 10-15 22:18

About this skill

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

Target Container entity Attachment to an occurrence Attachment to a type
Properties IfcPropertySet IfcRelDefinesByProperties HasPropertySets explicit attribute
Quantities IfcElementQuantity IfcRelDefinesByProperties HasPropertySets explicit attribute
Material IfcMaterial and the structured material entities IfcRelAssociatesMaterial IfcRelAssociatesMaterial
Classification IfcClassificationReference IfcRelAssociatesClassification IfcRelAssociatesClassification

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