## 4 Test Methodology and Evaluation Criteria of Data Interoperability
After conducting some preliminary tests on both simple and quite complex architectural models, different behaviour and a wide range of differences in the data exchange process were observed, particularly in the case of monodimensional members, such as beams and columns, whose utilization was independent upon the construction material. This circumstance led us to carry out complete interoperability tests on a very simple structural model, such as the 3D frame shown in Figure 1. It consisted of 4 columns and 4 beams and was designed in each CAD system using the same modelling approach; a preliminary model check was made by using internal tools, wherever available. In fact, an element to be considered was that, more often than expected, the lack of proven modelling guidelines and best practices was at the root of the interoperability problems. For quite complex projects, many different methods could be adopted to create, for example, a solid model using several combinations of union, intersection, addition, and subtraction features, but standard rules specifying the preferred modelling practices are important and design companies should train CAD users in the preferred methods for modelling parts and assemblies [46]. This refers specifically to mechanical CAD systems, but it can be applied to the AEC context, too. The main features of the 3D frame are listed below (dimensions in mm):  
1. Reinforced concrete columns, section size 300 \(\times\) 300, height 3000;
2. Reinforced concrete beam, section size 300 \(\times\) 600;
3. Material: reinforced concrete C28/35, according to Eurocode 2 (CEN, 2004). Before exporting the CAD model, a preliminary analysis was carried out to find the best conversion parameter settings to achieve an acceptable transfer by using IFC viewer tools, particularly BIMvision [47]. All the suggested settings for each environment that were available in the software help guides, and those recommended by international organizations, were adopted. The selection of the most appropriate options before translating the data via IFC was essential for the correct interchange of the model, both when importing and especially when exporting data. Most software offered the possibility to edit several parameters that could affect the resulting model. Each program had a different set of options, and during the benchmark the same options, if any, have been maintained. Four evaluation criteria were defined based on the interoperability studies available in the literature and reported in a matrix summarising the results. The geometric correspondence between the original model and the imported model was evaluated, determining the degree of fitting, possible distortions, missing elements, and position changing. The correspondence of the materials used was verified according to properties such as Young's modulus, density, and similar things. Other parameters were analysed, including the capability of reading and changing the most important characteristics of the elements such as dimensions, location between the points, dimensions, section type, size, and shapes. For  
Figure 1: View of the simple model created in Revit used for the benchmark. each of the aspects considered, a summary table was arranged to report the results based on a five-level score-evaluation system:  
1. Poor. Strong lack of correspondence between the exchanged information; data and/or geometry missing or hard to reconstruct in the receiving system; model affected by severe flaws that prevent its utilization. 2. Fair. Several losses of information needed for the immediate correct use of the model; the user needs to remodel and/or reassign key parameters. 3. Average. Most of the information is preserved; the model can be used after just a few changes; not much additional information provided. 4. Good. The correspondence of information is good, and after minor adjustments, the model is ready for analysis. 5. Excellent. Perfect matching of all information.