The data structure of BIM models serves as the organizational foundation for BIM information management and forms the theoretical basis for data sharing. BIM models primarily consist of three types of entities (ENTITY): model entities, graphic entities, and annotation entities.
1. To analyze the data structure of BIM models, it is essential to first understand the types and concepts of entities. Entity types correspond to data sets related to graphic attributes or drawing interface information. Entities of the same type share the same attribute types, but each entity can have distinct attribute information. Modifying a single entity’s attributes does not change the overall attribute type defined by that entity type.
An entity represents a specific shape within the scope of entity types, derived from detailed entity type attributes, corresponding to visible elements on the BIM model’s drawing interface—such as beam components or dimension annotations. The term “ENTITY” in English translates to Chinese terms like “graphic element” or simply “entity.” These entities not only form the BIM model but also include various attribute information, which constitutes the core intrinsic data of the BIM model.
2. Model entities are the primary components of BIM models, reflecting the geometric composition and internal relationships of buildings. Based on their characteristics, model entities are divided into main entities and component entities. Main entities exist independently within the BIM model and are unaffected by other entities. In contrast, component entities must be attached to main entities to exist and are limited by the main entities they connect to. For example, door and window entities in BIM models must be attached to their respective walls; without these walls, the doors and windows cannot exist independently.
View entities represent building views and related attribute tables visible within the model. These include floor plans, sectional drawings, elevation drawings, as well as reports and detailed schedules. Annotation entities cover visible annotation content on the drawing interface, such as grids, elevation markers, and text annotations.
3. Model entities serve as carriers for BIM information integration, dynamically consolidating various geometric and non-geometric data. When conducting measurements through a BIM model, the entity information must be accessed. Entities manifest as different components within the BIM model, so engineering measurements should be performed based on these components. Effective information management depends on the proper separation of model components.
To meet engineering measurement needs, component information is categorized into two types: basic information and extended information. Basic information comprises fundamental data specified by IFC standards, while extended information includes additional data added to support specific engineering measurement requirements by extending model entity information.
In summary, these entities collectively make up the BIM model structure. I hope this article provides valuable insights to all readers!
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