# A Systematic Review of the Trends and Advances in IFC Schema Extensions for BIM Interoperability
## 5 Evaluation of IFC Schema Extension Cases
### Analysis of Extension Cases by Product and Process Representations
#### 5.3.2 Detailed Analysis of Extension Approaches in the Infrastructure Domain
[93] introduced entities required for earthworks, while ref. [96] defined new entities to represent work in rivers (e.g., dredging). Process-oriented extensions:  
Using entity and property extensions. Numerous cases involved using both entity and property extensions to integrate various engineering analysis and management approaches in infrastructure BIM models. For bridges, refs. [72; 73] defined entities such as _IcfParametricProfileDef_ and _IcfParametricSketch_ to enable the addition of geometric and dimensional constraints, consequently enabling parametric modeling in bridge BIM models. Ref. [30] designed specific entities tailored to facilitate finite element analysis of bridge models. Other cases involved expanding the schema to incorporate processes for bridge inspection and maintenance. Ref. [76] extended the schema by introducing new entities to encapsulate bridge inspection data and explored methodologies for converting this new schema into ontologies to enhance information management. Ref. [75] established entities to systematically catalog degradation and data gathered during bridge inspection tasks. Ref. [74] broadened entity definitions to encompass asset management, creating schemas for various supplementary facilities. Ref. [77] crafted entities to store and utilize sensor readings in bridge O&M. Cases in the tunnel and road sectors were similar in defining entities to represent alignment and for operations and management. Specifically, refs. [65; 66] defined entities specifically for tunnel alignment, while ref. [67] focused on designing entities for tunnel O&M information. For the roads sector, refs. [74; 81] also defined separate entities for road alignment, while ref. [82] defined entities for road operations management. Studies were also performed in the rail sector exclusively for set requirements. Ref. [88] proposed new entities to represent rail geometry, such as transition curves and chainage systems, while ref. [85] defined entities and related properties to represent alignment concepts of railways. Ref. [76] developed entities to represent sensors affixed to railway facilities, which were used to collect O&M data. Several studies have focused on creating representations for entities within specialized fields. Ref. [94] developed entities to encapsulate critical scheduling and quality data generated during the foundation construction phase, while ref. [95] introduced supplemental entities to effectively represent georeferencing data. Three cases were sector-agnostic: Ref. [14] created the 'IFC Monitor' extension to facilitate the transfer of BIM-based structural health data, introducing unique entities for sensors and their network structures. Ref. [89] devised extensions to incorporate concepts and processes in public-private partnerships (PPP) projects, while ref. [90] developed extensions tailored to steel reinforcement product details and manufacturing information. Using property extensions (exclusively). Three cases existed in which property extensions were solely utilized to represent processes. Ref. [71] utilized property sets to describe the semantics for the physical and spatial components in a steel box girder bridge. Ref. [83] defined property and quantity sets to describe the protocols for quantity take-off of road facilities. Ref. [92] used propertiesand _IcfProxy_ to streamline finite element analysis on IFC-standard geometric models. It is worthwhile to note that these cases appropriated entities from the architecture domain as substitutes or proxy entities, as formal IFC entities for their respective sectors did not exist at the time of their research. In summary, most cases in the infrastructure domain utilized 'entity and property extension' approaches to develop both product and process representations. Product representation efforts mainly focused on defining elements to cover the sectors missing in the standard schema with respect to infrastructure.