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Attribute facet

Every entity in an IFC model has a list of standardised Atributes. Attributes are a limited set of fundamental data (usually less than 10) associated with all IFC entities. These are fixed by the IFC standard and cannot be customised.

Here are some common attributes and what they mean:

  • GlobalId: a unique ID for the element useful for computer geeks
  • Name: a short name, code, number, or label to identify the object for a human. If you had to annotate the object on a drawing or a schedule, the Name is what you should see. For example, a pump Name might be P-10-A.
  • Description: typically the longer form of the name, written to be descriptive and readable for humans. For example a pump Description might be Water Suction Pump.
  • Tag: this is an ID that may link it back to another BIM application. For example if the IFC model was produced using Revit or ArchiCAD, it might hold the Revit or ArchiCAD element ID.

Information that is not critical to the definition of the IFC entity is stored as a Property, not an Attribute. For more information view the documentation on the Property Facet.

For this reason, Attributes are a good way to specify an Applicability to specific elements, or specify a Requirement that certain elements shall be identified, named, or described in a particular way.

To see what Attributes are available for an IFC class and what their potential values may be, you will need to check the IFC documentation. Here is how you might find a list of valid Attributes for the IFC4X3 schema. The instructions will be similar for all IFC versions.

  1. Browse to the documentation page for the IFC class you are specifying. For example, this is the IfcWall documentation page.
  2. Scroll down to the Attributes section of the documentation. Note that by default, not all attributes are shown. Press "Click to show hidden inherited attributes" to show all attributes. For IFC4, click on the "Attribute inheritance" text header to toggle a table for all attributes.
  3. The Attributes table will show the Name of each Attribute. Note that Attributes which do not have a number next to them and are in italics are not allowed to be specified. Only enumerated Attributes may be specified. For example, you may specify the Name attribute for an IfcWall, but you may not specify ConnectedTo.

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

Following naming conventions and accurately describing elements are critical to many usecases in the AECO industry. For this reason, it is very common to use the Attribute Facet in both the Applicability and Requirements section of Specifications.

Parameters

Parameter Required Restrictions Allowed Allowed Values Meaning
Name ✔️ ✔️ A valid attribute name from the IFC schema. The attribute must exist and have a non-empty value.
Value ❌ ✔️ Any value appropriate to the data type of the attribute The value of the attribute must match exactly. To specify numbers, you must use a dot as the decimal separator, and not use a thousands separator (e.g. 4.2 is valid, but 1.234,5 is invalid). Scientific notation is allowed (e.g. 1e3 to represent 1000). To specify true or false, you must specify TRUE or FALSE as uppercase characters.

Examples

Applicability Intention Requirement Intention Facet Definition
Any entity with a Name of "ABC123" The entity (e.g. Project) must be named "ABC123" Name="Name", value="ABC123"
Any entity (but typically IfcMapConversion) with an Easting of 312345 The entity (e.g. IfcMapConversion) must be geolocated such that the origin is at the Easting of 312345 Name="Easting", value="312345"
Any entity with a name starting with "WT" followed by 2 digits, such as WT01, WT02, etc. The element must have the naming scheme of WT01, WT02, etc Name="Name", Value="WT[0-9]{2}"
Any entity with a non-empty Description The entity must have a description Name="Description"
Any entity (typically an IfcTask) with a Status set to either "NOTSTARTED", "STARTED", or "COMPLETED" The entity Status (e.g. for an IfcTask) must be filled out with either "NOTSTARTED", "STARTED", or "COMPLETED" Name="Status", Value=["NOTSTARTED", "STARTED", "COMPLETED"]
Any entity (typically an IfcTaskTime) with a DurationType set to WORKTIME (i.e. based on a calendar) The duration type (e.g. for an IfcTaskTime) must be based on a calendar, not elapsed time Name="DurationType", Value="WORKTIME"