# Envisaging a European Digital Building Renovation Logbook: Proposal of a Data Model
## 3 Results
### Core Entities and Associate Characteristics  
Within this category, there are three root entities--\"City\", \"Building\", and \"BuildingUnit\"--which are related directly or indirectly with all the entities of the model (Figure 5). \"Building\" and \"BuildingUnit\" are independent so that the model can be applied to buildings of different nature, i.e., single-unit buildings as well as buildings made up of different units, such as multi-family residential buildings or office buildings. The distinction between these entities, despite not having been considered by most of the DBL previous initiatives, is highly relevant and thus has already been applied in the guidelines for the INSPIRE cadastres and mentioned in the proposal for the EBPD recast [1; 31]. The INSPIRE cadastres constitute georeferenced datasets generated and managed by the registers of MS. This is done in adherence to the INSPIRE Directive, ensuring their compatibility and usability in both community and cross-border contexts [51]. Hereunder, the tables of core category are explained, whereas specifications on attributes are presented in Appendix A.1.  
* In the \"City\" entity, the geographic area or locality where the building is placed is identified. To define addresses, the INSPIRE cadastre establishes administrative units within each MS ranging from level 6 to 1. This aims to standardise the definition of addresses across the entire EU. Level 1 refers to the largest administrative unit, which  
Figure 5: Core category of the proposed conceptual relational data model for the DBrL.  
is the country itself, while as the level increases, the scale decreases until reaching the smallest territorial administrative unit in each country [32]. In this paper, we considered national level 3-4 administrative units according to the INSPIRE cadastre, which correspond to the municipality. Within this entity, the outdoor environmental conditions that affect the building, such as national climatic zone, and heating degree days, are identified.
* The \"Building\" entity refers to enclosed constructions above and/or underground that are intended or used for the shelter of humans, animals, things, or the production of economic goods and that refer to any structure permanently constructed or erected on its site [31]. In this entity, general information on the building is provided as well as some documents and certificates that refer to the whole building.
* \"BuildingUnit\" refers to a property of a part of a building, either residential or non-residential [51]. It may include dwellings, offices, common areas, etc., and sometimes, it can be coincident with the building, for example, in single-family residential buildings.  
Regarding the link between entities, \"City\" and \"Building\" are connected through a 1:N relationship since in each city, there are many buildings, but each building can be placed in only one city. Similarly, entities \"Building\" and \"BuildingUnit\" are also linked through a 1:N relationship because in each building, many building units can be found, but each building unit can belong to just one building. The primary key used in each case is bold in Figure 5.