## 3 State of the Art
### Industry Foundation Classes  
The Industry Foundation Classes (IFC), defined in the IFC Specifications Database [23], is a standardized data structure that allows for the transfer of information within various systems using digital models employed in the construction sector. It facilitates a seamless exchange of data using several IFC file implementations (formats). The IFC structure encompasses various types of properties or attributes, including geometric data, physical properties, environmental-related information, and other relevant characteristics. BuildingSMART and ISO have continuously updated IFC to address the changing requirements of contemporary building and infrastructure projects. The first official version of IFC, released in 1997 (IFC 1.0), established a framework for representing and exchanging construction and facility management data. BuildingSMART commenced a collaboration with the International Organization for Standardization (ISO), which culminated in the publication of the document ISO/PAS 16739 [24] in 2005. BuildingSMART and ISO continued their cooperation and published the first version of IFC as an international standard: ISO 16739:2013 [25]. This standard was revised in 2018, and the current edition was published in March 2024 as ISO 16739-1:2024 [26]. The latest international standard corresponds to IFC 4.3 ADD2 version according to buildingSMARTnaming convention and includes, among other improvements, a schema for civil engineering projects, allowing IFC to cover more typologies of construction assets. There are two versions under development: IFC 4.4, improving the structure of IFC 4.3, and IFC 5, which will change the approach of the data structure. However, the present study concentrates exclusively on IFC 4.3, disregarding the versions currently under development. This decision is based on the objective of concentrating the assessment on a finalized version, one that may incorporate feedback from industry based on actual experiences. IFC uses the Standard for the Exchange of Product (STEP), defined in ISO 1030 set of standards, to transfer product data across different software applications and computer systems. The IFC definitions are documented using EXPRESS (defined in ISO 10303-21:2016 [27]), a conceptual schema used to specify classes for a defined domain, the data, attributes or constraints relevant for certain classes, and also the relations between classes. An XML implementation of the STEP format based on ISO 10303-28:2007 [28] can be used for IFC data representation and exchange. The IFC data formats and their internal mappings are described in [PERSON], [PERSON] and [PERSON] [29]. The IFC schema is organized into four conceptual layers, as described by buildingSMART [30] and [PERSON] et al. [31]:  
1. The domain layer is the highest layer, facilitating the intra-domain exchange and sharing of information, providing model details for a domain process or a type of application (e.g., structural engineering or HVAC). It encompasses schemas that comprise entity definitions, which represent specializations of products, processes or resources that are discipline-specific. 2. The interoperability layer facilitates the inter-domain exchange and sharing of construction data across different architecture or engineering disciplines, providing definitions of concepts or objects common to different domains or applications. It encompasses entity definitions that are specific to the general product, process, or resource specializations applicable across multiple disciplines. 3. The core layer provides the basic structure of the IFC object model and defines the abstract concepts that will be defined in higher layers. It incorporates the kernel and core extension schemas, including a globally unique identifier (GUID) for all the entities and other relevant information. 4. The resource layer is the lowest layer, facilitating the definition of individual schemas containing resource definitions for geometry, material, quantities, etc.