During the design phase of a building, a series of geometric descriptions are made based on input parameters (lengths, size, location, orientation). These parameters are commonly also part of the non-geometric description, causing redundant information. In traditional descriptions, such as the Industry Foundation Classes (IFC), this can lead to the non-geometric description contradicting the geometric one, since they are not updated accordingly. For example, a wall can be defined in IFC, where the height of the wall is a non-geometric property, while the extrusion of the geometry is stored separately. The non-geometric property is neither connected to the extrusion nor
automatically updated, when the geometry changes, resulting in the potential of inconsistent data. Thus, a link between related properties from geometric and non-geometric descriptions should be established, to ease the detection of contradicting data and the subsequent updating process. In the Ontology for Managing Geometry (OMG, https: //w3id.org/omg), a first implementation of
such links is realised. For one, the omg:isExplicitlyDerivedFrom property can be applied in cases, a geometric property of RDF-based geometry (object) and a non-geometric (subject) property describe exactly the same situation (e.g. the height/extrusion), where a chain axiom can be used to automatically update the according values. On the other hand, the omg:isImplicitlyDerivedFrom property can be applied to indicate that a non-geometric property (subject) can be derived from a geometry description (object), as is the case for volumes or surface areas.

• Remark: adding metadata regarding the used coordinate system, units and other metadata as mentioned in extension 1 and 4 can also result in double information. Some geometry schemas such as OBJ are unitless so additional info on the length unit is useful, while others allow to define the used units internally (e.g. STEP) or have a fixed length unit defined in the schema (e.g. glTF uses metre). Adding metadata in RDF for OBJ geometry description enriches the knowledge over the geometry. If this is also added for STEP or glTF geometry, this results in redundant data, but the metadata is now externalized in RDF can thus be queried directly (no interpretation needed).