# A Unified Database Solution to Process BIM and GIS Data
## 3 Results  
### The Concept of an Integrated BIM/GIS Database Environment  
As discussed in Section 2, many attempts were made to exchange data between BIM and GIS, as well as to create a common database based on a unified data model. The use of the new common data model by BIM and GIS requires the introduction of quite radical changes in the applications available on the market; therefore, the implementation of this solution will likely take many years. The concept proposed in this article assumes a pragmatic approach, which minimizes this shortcoming by using IFC and CityGML schemas in their practically original forms in a single database, later referred to as the Integrated BIM-GIS Database (BIGI-D). The integrated database does not mean in this case a single consistent database in the sense of a conceptual model but a coherent technological environment that allows, depending on the needs, the use of data from both resources by various applications and the improvement of the methods of full information exchange. Thus, the proposed method does not solve the problem of describing the same objects in the BIM and GIS by classes with different structures. On the contrary, it assumes that the conceptual (structured) discrepancies will still exist for some time and that solutions should be sought that accept this situation and improve the coexistence of BIM and GIS until fundamental changes are introduced. At the stage of implementation, BIM data saved in accordance with the IFC conceptual model are processed using tables, perspectives, and stored procedures in the IFC schema. The term schema is used here in two ways--as a data structure and as a place to store tables and procedures in the database. In the proposed technological approach, the use of stored procedures is essential. A stored procedure is a set of SQL (Structured Query Language) statements with its name, which are stored in a database management system as a block. A stored procedure is a subroutine available to applications that access a relational database management system. GIS data recorded according to the CityGML conceptual model are processed using tables, perspectives, and stored procedures in the CityGML schema. In addition, it is proposed to add the BIM-GIS Schema (BIGI-S) for joint storage of the data from IFC and CityGML to facilitate conversion between BIM and GIS and data sharing. All three schemes are implemented in one database. A model based on dynamic data conversion is an alternative implementation solution. Within this approach, the data are only stored in the BIGI-S. Schemas dedicated to individual BIM and GIS applications (as well as others) are implemented as database views and stored procedures. The schema dedicated for the BIM application is generated on the fly, based on stored procedures that convert data from the BIGI-S. The case with the CityGML schema is similar. The main advantage of this solution is the elimination of data redundancy. Each object is saved in the database once but can be seen using CityGML and IFC views. From the point of view of BIM and GIS applications, the common BIGI-S is, in this case, completely invisible. Each of these applications read data using the appropriate IFC or CityGML model. The weakness of the above solution is the need to create complicated database perspectives that realize the translation of selected data between schemas, in the case of spatial data conversion to IFC, while requiring very fast access to these data. Despite the necessity of creating complex perspectives and stored procedures, the authors claim that avoiding redundancy has significant value; therefore, this solution was selected for the prototype. However, such a solution may adversely affect the efficiency of processing. Therefore, preliminary studies on the effectiveness of using stored procedures for model conversion were performed. The architecture of the proposed database includes the possibility of creating a number of additional schemas (e.g., a schema for facility management systems) that use both BIM and GIS data.