Property facet

IFC Properties are the most common way to attach data to objects in IFC, and likely the most used IDS facet.

Properties are identified by a name (BaseName in IDS), such as "FireRating", and are grouped into Property Sets, such as "Pset_WallCommon" that help keep them organised by similar subject matters. IFC Properties have Values, which are of particular types, which, if relevant, express units.

buildingSMART provides standardised Property Sets and Properties to help seamless data exchange, by mandating the name, set and data type. For example:

Users can also define custom Properties and Property Sets, which may be unique to the project or distributed using the Property Set templates feature of IFC. Naturally, it is encouraged to require Properties that are standardised by buildingSMART before inventing custom ones.

All standardised Property Sets start with the reserved prefixes "Pset_" or "Qto_"; these prefixes are prohibited for custom properties.

Standardised Properties apply to different entities. For example, some properties such as LoadBearing can be applied to walls, columns, and beams, but not furniture, ducts, or cables. This is known as the Applicable Entity. When specifying Properties in an IDS, it is important to consider which objects they can apply to. All sorts of objects can have Properties applied, not only physical objects like doors, windows, and slabs, but also non-physical objects like tasks, materials, structural profile cross sections, or labour resources.

A special kind of Property is known as a Quantity. Whereas Properties refer to any arbitrary information about an object, Quantities refer specifically to calculated dimensions of the object, such as length, width, height, surface area, or net volume. IFC makes a distinction between Properties and Quantities, but in IDS they are interchangeable, and you are allowed to specify Quantities just the same as a Property with this facet. Just like Properties, Quantities are grouped into Quantity Sets and have a Value.

To see what Properties are standardised by buildingSMART, check the following lists below. You will see a list of Property Sets. Clicking on a Property Set will bring you to its page, which will show the Applicable Entity just below the page title, as well as a table of Property Names and expected data types for the Values and have an Applicable Entity.

• IFC4X3_ADD2 Property and Quantity Sets
• IFC4 Property Sets
• IFC4 Quantity Sets
• IFC2X3 Property Sets

Note that IFC2X3 only has buildingSMART standardised properties, not quantities.

Instead of checking the documentation, your IDS authoring software may help you to shortlist valid Property Sets.

Supported types of properties

There are various types of properties in IFC. The IDS allows specifying simple single values, bounded values, lists, tables, and enumerations, while complex properties and reference values are not supported by IDS.

The interpretation of a list, table, bounded and enumerated property changes depending on the IDS requirement as follows:

• If the IDS value is a single value, at least one of the IFC values should match.
• If the IDS value is a restriction (with minExclusive,maxExclusive,minInclusive,maxInclusive), all IFC values should respect the range.

Because IFC bounded value properties can be limited on one end only, for them to meet IDS requirements, they must be entirely within the IDS restriction range. For example:

Property data types

In IDS facets, Properties may have a data type that constrains the expected format in which the property will be stored (e.g. text value, a boolean, or a number). If it is a number, the value will be unit-less, such as a count of a value and the unit dependent on the measure associated with the specified dataType. Our unit documentation provides the list of acceptable measures and the SI unit used for their expression. For more information, consult the IFC documentation at the following links:

• IFC4X3_ADD2 data types
• IFC4 data types
• IFC2X3 data types

For convenience, a short list of common data types is here:

IDS currently specifies all measure-based values based on SI units. You can see the full list of units specified for each data type in the IDS units table. Note that although you can use a data type to request a particular measurement (e.g. an IFCLENGTHMEASURE), you cannot use IDS to request that the length is measured with a particular unit (e.g. meters, inches, or millimetres).

Properties are critical in providing supplementary information to objects in a model.

It is encouraged to follow buildingSMART standardised Properties wherever possible to ensure that data is highly structured and can be predictably retrieved.

Parameters

Examples

Properties

Required fields

Both propertySet and baseName are mandatory. Both dataType* and value are optional, but if value is provided, it also requires dataType*. The optional attribute uri is only metadata, not subject to IDS checking.

Property facet interpretation

Applicability

Requirements

* The field is an XML attribute