## 1 Introduction  
The AEC (architecture, engineering and construction) industry is experiencing a revolution due to the fast development of the building information modelling (BIM) sector. BIM represents a new paradigm of the construction process and asks for novel answers to the problems of data sharing and intellectual property rights definitions [1]. It is a complex platform aimed at preserving all relevant information related to any phase of the construction lifecycle and needs several, heterogeneous data-exchange capabilities. As a result, the interoperability (i.e., the ability to exchange any kind of data between applications), which smoothens the workflow and often facilitates automation, is the key feature of the process [2]. The demand for interoperability between different software packages has experienced increased growth in the AEC market [3], especially in Europe, where regulatory bodies have issued new rules for the digitalisation of the civil engineering sector [4; 5; 6]. The mandatory use of the BIM platform on a large scale has expanded the need for easy and reliable information-exchange processes that are able to preserve data and their quality and has increased the importance of a substantial integration of the various disciplines related to the AEC world [7; 8; 9]. Full interoperability is what is expected in any design context where several software packages are adopted by users and a set of local or national authorities are required to interact with all the players in the process. As far as the design of new structures is concerned, architects and engineers closely collaborate on a construction project. Architectural design is commonly performed in a modelling environment termed computer-aided design (CAD), whereas engineering design takes place in a simulation and analysis environment called computer-aided engineering (CAE). Therefore, the transition from CAD to CAE is one of the basic phases of the BIM process. A common trend in the design process is towards a fully integrated design environment that combines geometric modelling tasks with computer simulation tasks, until the final design is delivered. Given effective and reliable software interoperability, it is theoretically possible to directly switch from a CAD model to a CAE one. This is possible if all the software tools can share information taken or extracted by the same digital legacy model. It is worth noting that interoperability is a complex concept and cannot be uniquely defined. A first general distinction is made based on the path of the user workflow [10]. _Horizontal interoperability_ is defined as a data exchange between two architectural BIM software environments, such as the CAD-to-CAD path. _Vertical interoperability_, on the other hand, refers to a data exchange between architectural and structural software environments, such as the CAD-to-CAE path [9]. What is required more and more is the need to work in a bilateral environment in which the data exchange occurs bilaterally from/to any computer-aided (CAx) environment (i.e., CAD-to-CAE-to-CAD). As reported in [11], two main types of data transfer paths between two design environments exist depending on the way the information is exchanged:  
* Direct link (DL) uses an automatic connection between two different software environments by a plug-in expressly released for that purpose. Data from the sending environment are mapped onto the data from the receiving environment; thus, no external intermediate data translator is needed, and the exchange process appears to be highly efficient, even though it depends upon proprietary formats. * Neutral link (NL) consists of adopting an independent exchange format; it is the most appropriate approach to a BIM-oriented methodology and represents a key step for the BIM environment. Most data that describe buildings, related to the building disciplines and to the several phases of the building lifecycle, are collected and managed by a neutral format.