## 5 Summary of the Interoperability Tests
### Use of IFC 4 Design Transfer View (DTV)  
This section reports the results of the tests using the IFC 4 format with the Design Transfer View (DTV) schema. The same native geometric model as is represented in Figure 1 was exported in the IFC 4 DTV format and then imported into the CAD/CAE environments. According to Tables 3 and 4, not all programs could import/export the IFC 4 format, so the test was limited to a few combinations. These tests were conducted to assess the possibility of using IFC 4 to overcome the issues mentioned above, related to IFC 2x3. Tables 8 and 9 report the results. All the exported models were validated with BIMvision.  
* **Revit.** In general, there were no significant differences between IFC 4 DTV and IFC 2x3 CV 2.0. The self-test was still not completely successful because of the change of total entity number depending on the self-test sequence and the loss of the original _ifcBeam_ and _ifcBeamType_ entities in the first self-test round. In addition, Tekla Structures correctly imported the model, but as a single block instead of separated elements. Consequently, the imported model was not modifiable in terms of the properties and geometries but was represented only as a reference model. The same behaviour occurred for ArchiCAD and Allplan towards Tekla. RFEM reported an error, stating that _IfcColumn_ and _IfcBeam_ were entities that could not be imported: only analytical elements were expected, e.g., _IfcStructuralCurveMember_, which is able to describe edge members (straight or curved), such as beams, columns, rods etc.
* **ArchiCAD.** The same considerations were true for ArchiCAD for the horizontal interoperability: the geometrical model was correctly imported, but a few parameters (section sizes or dimensions) were not always editable. The same behaviour was exhibited for CAE software receiving the IFC 4 model generated in ArchiCAD as for the IFC 2x3 model. In SAP2000, beams were rotated 90\({}^{\circ}\) around their axis.
* **Allplan.** Allplan could export/import in the IFC 4 format in the last release (B) we tested, but was unable to import in that format in the first release, A. For the export format, the same considerations as for IFC 2x3 applied. In RFEM, although the software could import IFC 4 files in release A, an error message appeared while reading the IFC file and no data was imported. In release B, the same software could read the model, but inaccurate positions for the columns and beams were generated, so a poor score was assigned to this test (Figure 7), as was true for IFC 2x3, reported in Figure 4.  
between release A and B displayed an improvement in the performance of the data transfer over time; data related to the geometry, the cross shape, the dimensions, and the insertion point were, indeed, correctly transferred and processed by the release B CAD receiving software.  
An issue was still observed in the material data transfer, since in this case the label was correctly transferred to the receiving software, but all the structural and physical properties were lost. It is worth noting that in all cases, the entities could be manipulated and changed in the receiving CAD environment, enabling the implementation of an effective optimisation of the design process. Revit reconstructed the imported model well but could not modify the elements. ArchiCAD, on the other hand, could correctly import the geometrical model from SAP2000 and all elements were editable. Allplan and Edilus in the release A version were not compatible with the IFC 4 DTV format. The current release B of the Edilus software package maintains such a limitation; conversely, this issue has been fixed in the renewed version of Allplan. A final comment can be devoted to the performance of RSA and ModeSt, which lacked interoperability based on the IFC 4 schema both in input and output operations; the case of Edificius was better, with the software in this case being able to read IFC 4 files but unable to export in the same format, thus limiting the required interoperability of the design process.