As part of the Government Industry Interoperability Group, NBS undertook an alignment exercise between Uniclass and Industry Foundation Classes (IFC), to support the industry in assigning classification. IFC is an open-standard file format used to exchange data between different software applications and defines a data schema for representing building and construction industry data, including geometry, relationships and properties.
Where additional information is required to meet specific project or industry requirements, user-defined IFC property sets can be created. Manual intervention is required to ensure that this information is successfully exported in a consistent manner. The principles in exporting ‘NBS interoperable data’ are introduced below.
User-defined property mapping
The NBS BIM Object Standard provides a solid foundation in consistent property selection and grouping in proprietary design software, but the requirements of different software or standards require these to be mapped to enable a seamless data exchange. For example, for the exchange of COBie information, reference should be made to NBIMS-US v3, annex A and the defined mapping rules that need to be followed.
During the Revit® to IFC export, properties and their groupings need to be defined by an external mapping file to ensure that these are accurately represented as an output. To comply with the NBS BIM Object Standard and the requirements of NBIMS-US v3, annex A, the following property groupings should be followed:
- NBS_General
- NBS_Specification
- COBie_Asset
- COBie_Component
- COBie_EconomicImpactValues
- COBie_ServiceLife
- COBie_Specification
- COBie_Warranty
- Pset_ManufacturerOccurence
- Pset_ManufacturerTypeInformation
NOTE 1: The naming of these property sets is unique to the originator and should not be altered.
Figure 1 – Example Revit® property mapping file
It is essential to define custom IFC property sets in a structured and standardized manner to ensure consistency and meaningful use of the additional data. Grouping properties will provide consistent IFC outputs for all projects that utilize NBS digital objects and their inherent data from NBS Source.
Assigning classification to modelled objects
With so much information being available at our fingertips, there also needs to be a robust classification system adopted to enable efficient information retrieval. Uniclass integrates seamlessly with IFC, offering a range of benefits that improve information management. These include:
- More detailed and organized representation of building elements.
- The promotion of efficient exchange among various stakeholders.
- Consistent model interpretation, avoiding misunderstanding.
The IFC2x3 TC1 schema includes inherent IFC Entities and their attributes used for classification:
- IfcClassification
- Source
- Edition
- EditionDate
- Name
- IfcClassificationReference
- Location
- ItemReference2
- Name
NOTE 2: The IFC4 Add2 schema includes the inherited attribute ‘Identification’.
In depth knowledge of the IFC schema(s) is not required to understand how classification is assigned to modelled objects. Instead, the information is populated in the classification settings:
Figure 2 - Revit® classification settings interface
Revit® exports IfcClassificationReference data from a single user-defined parameter, which includes both the code and title (separated by a colon). Spaces can be included before or after the colon (or both), such as Pr_30_59_98_02 : Aluminium window units, and Revit® will automatically split these into the ItemReference and Name fields during the export process.
Uniclass is updated every quarter; therefore, it is important that the Edition is entered to coincide with the version of the tables used on a project. The latest tables can be downloaded here.
Multiple user-defined classification parameters can be utilized if required, for example the inclusion of Systems, Products and Spaces/Locations classification for modelled elements. In these instances, the parameters can be entered into the Classification field name (separated by commas). This is particularly useful where classification is required at Type and Instance level.
The two NBS Chorus shared parameters indicated in Figure 2 have been used for Component and Layered objects and Rooms:
| 1. | NBSChorusCategory | Type |
| 2. | NBSChorusCategory_mtrl3 | Instance |
Table 1 – NBS classification Revit® shared parameters
NOTE 3: The property is used for Revit® material association purposes but has been utilized to avoid creating additional instance parameters.
Further information on NBS Chorus properties can be found in the technical article here.
The result is that every modelled object with one of these properties associated will have classification data automatically embedded in the IFC model.
Figure 3 – Example classification hierarchy in IFC file
Sample BIM tools
Access the example NBS files used to demonstrate interoperability.
