IfcPropertyDefinition and IFC data schema: here’s how to read, edit and add properties to objects in an IFC model
In this post we’ll be dealing with the third pillar of the IFC schema, the
IfcPropertyDefinition or the mechanism that defines the generalization of information (set of properties) that may be assigned to multiple instances of objects.
- IfcObject (IFC schema part 1)
- IfcRelationship (IFC schema part 2)
- IfcPropertyDefinition (IFC schema part 3).
The IFC model hierarchical structure
The IFC schema represents a sort of storage system that saves building-object related information ensuring access to the information asset over time and without any restrictions. The IFC standard file structure basically configures a model consisting of hundreds of entities organized hierarchically.
IFC models are described according to the schema objects in three broad categories:
IfcObjectDefinitionand its derived entities, used to implement the definition of the object
IfcRelationshipand its derived entities, identify the definition of relationship
IfcPropertyDefinitionand its derived entities, allow model users to define and use data-driven properties with entities.
The subtype hierarchy of the
IfcPropertySetDefinitionthat is the generalization of property sets.
IfcPropertySetthat represents a supertype of property sets. These properties are defined and qualified by name. Property sets are assigned to objects
(IfcObject)by means of the
IfcPropertythat defines the generalization of the property types that can be associated to IFC objects and depends on a property set.
IfcProperty, further subtypes include:
IfcComplexPropertywhich is used to define complex properties to be managed within a property set
IfcSimplePropertyqualifies the properties assigned to a single object. Various subtypes of the
IfcSimplePropertydetermine the different ways in which a property value can be set.
IfcSimpleProperty incorporates 6 different subtypes that are listed below.
defines a property object which has a single value assigned through numeric or descriptive elements:
- Nominal Value
- Type (through IfcValue)
Example of a property with single value to describe a 4 cm thick door, with transmittance value of 2.6 w / (m² K) that is produced by “Manufacturer A”:
defines a property object with an assigned value which is chosen from an enumeration. The property-value combination is specified within the
IfcPropertyEnumerated class, which is a subtype of the
Here is an example:
defines a property object which has two (numeric or descriptive) values assigned: the value specifying the upper bound and the value specifying the lower bound.
This property could, for instance, determine size and weight dimensions of an object to be moved in a construction site.
defines a property object which has two lists of values assigned, which specify a table with two columns. The values shown in the first column establish the scope of application for the values in the second column
For example, the table below illustrates the values of sound transmission loss within a certain range.
assigns a value to the property set through a link with predefined complex properties within the IFC schema.
defines a property to which multiple values are assigned. These values are given by a precise and ordered list (the order in which the values are displayed is significant). Each value in the list is unique and duplicate values are not allowed.
The listed property values could, for example, determine the dimensions to produce a specific construction.
Examples of properties associated to entities
The figures below show some examples of properties associated to entities as represented in the usBIM.viewer+ working space.
Specifically, in the first figure you can see a door object selected in the left-hand side toolbox; while in the toolbox to the right, you’ll be able to read the entity related properties.
The second figure (Figure 2) illustrates how to add a property to entity sets. Simply launch the IFC model editor, then by selecting two entities from the properties dialog box, you can easily insert a new surface “painting” property associated to the
Figure 3 shows how to modify the volume properties included in the
IfcWallStandardCase, switching it from “White plaster” to “Bush-hammered white plaster”.
Finally, the fourth image shows you how to check the inserted properties: by selecting the wall entity on the
IfcWallStandardCase node, you can read the changes applied in its properties in the toolbox to the right. These are the painting with “colour” attribute and the changes to the “plaster” attribute.
IFC viewer download
If you’d like to analyse the
IfcProperty assigned, to insert and/or edit a building’s entities such as wall, slab, window, door, etc., simply download usBIM.viewer+freeware.
For further info on this topic, you can read these other articles: