IFC is currently recognized internationally as a BIM standard. Many BIM software platforms adopt IFC as the standard for data exchange. I have previously shared related articles, and today I will introduce the four levels of the BIM standard IFC.
1. Resource Layer
The resource layer represents the lowest level of the IFC architecture. The classes defined at this level are fundamental, low-level concepts and objects that can exist independently without relying on other classes. The resource layer schema, developed in IFC Release 2.0, includes measurement data, utility data, geometry data, object properties, and property types. Release 2.0 also partially restructured and expanded the content from Release 1.5.
2. Core Layer
The core layer is the second level in the IFC architecture. Categories defined here can be referenced and specialized by all categories in the interface and domain/application layers. This layer provides the basic structure of the IFC object model and defines the majority of abstract concepts. The core layer itself contains two levels of abstract content: the Kernel and Core Extensions.
(1) Basic Core
The basic core includes all fundamental concepts required for the IFC object model, defining its structure and components. These abstract concepts are essential for higher-level use and cover object relationships, type definitions, properties, and rules.
(2) Core Extension
The core extension includes additional or specialized concepts building upon the basic core. It provides necessary information for industries related to construction and facility management. Each core extension specializes in categories originally defined by the basic core.
3. Interface Layer
The interface layer defines concepts or object modules shared across different domain/application models. Its main categories include shared building elements and shared building service elements.
4. Domain/Application Layer
This is the highest level of the IFC architecture, offering object models required for construction and facility management. Currently, the domain models defined by IFC include Architecture, Facility Management, Cost Estimation, and HVAC.
The IFC architecture follows the ladder principle: categories at each level can reference categories at the same or lower levels, but not higher levels. The details are as follows:
1. Resource classes can only refer to or use other resource classes.
2. Core classes can reference other core classes and any resource classes. However, they cannot reference categories from the interface or domain/application layers.
3. The core layer itself follows the ladder principle: basic kernel classes can be referenced or used by classes extended from the kernel, but not the other way around. The basic core cannot reference core extension categories.
4. Interface layer categories can refer to any category in the core or resource layers, but not to categories in the domain/application layer.
5. Categories in the domain/application layer can refer to any category in the interface, core, or resource layers.
That concludes my introduction to the four levels of the BIM standard IFC. Since domestic BIM standards are still under development with no clear release date, international standards like IFC remain dominant. However, considering the unique characteristics of China’s construction industry, these international standards often face challenges when applied locally. Therefore, developing BIM standards suited to China’s national context will play a crucial role in advancing BIM implementation.
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