A Classification System is a defined hierarchy to categorise elements. An example popular System is "Uniclass 2015". Within a System, there is a hierarchy of short Reference codes that categorise elements in increasing levels of specificity, such as "EF_25_10" and "EF_25_10_25". Any object in IFC model can have a Classification Reference.
The Classification Facet is different to the Entity Facet. The Entity Facet is restricted to built-in IFC classes and predefined types, which may also function as a method of Classification. In contrast, a System specified in the Classification Facet refers to a third party, non-IFC System.
IFC models keep track of Classification names, dates, versions, and other data to uniquely identify the System, and may even store the hierarchy of References. For this reason, Classification requirements should use the Classification Facet, as opposed to the Property Facet.
Classifications are a great way to identify Applicable entities, or Require that entities should follow a nominated Classification system by a workflow, such as in an asset management system, work breakdown structure, or coordination requirement.
| Parameter | Required | Restrictions Allowed | Allowed Values | Meaning |
|---|---|---|---|---|
| System | ❌ | ✔️ | The name of the Classification System | The element must be classified with a reference that is part of a classification system with this name |
| Value | ❌ | ✔️ | The value of a Refeference code in the Classification System | The element must be classified with a Reference which has a code that matches this value. The value is typically a short code with a separating character that denotes the level of classification |
If no parameters are specified, then it means that any Classification should be present, regardless of System name or Reference code.
| Applicability Intention | Requirement Intention | Facet Definition |
|---|---|---|
| Any classified element | The entity must be classified | No parameters |
| Any entity classified using OmniClass | The entity must be classified using OmniClass | System="OmniClass" |
| Any entity classified with either OmniClass or Uniclass 2015 | The entity must be classified using either OmniClass or Uniclass 2015 | System=["OmniClass", "Uniclass 2015"] |
| Any entity with a classification reference of "EF_25_10_25" | The element (e.g. a wall) must be classified using the reference "EF_25_10_25" | Value="EF_25_10_25" |
| Any element with a Uniclass 2015 classification reference starting with EF_25_10 | The entity (e.g. a wall) must use Uniclass 2015 and have are reference starting with EF_25_10 | System="Uniclass 2015", Value="EF_25_10.*" |