No-Schema Algorithm for Extracting a Partial Model from an IFC Instance Model

This paper proposes an algorithm for extracting a partial model from an Industry Foundation Classes (IFC) instance model without an IFC schema or a complete IFC model view definition (MVD). The methods developed in previous studies require either an IFC schema or MVD and software applications, such as an IFC model server or a building information modeling (BIM) authoring tool, to extract a partial IFC instance model. The algorithm proposed in this paper generates a partial model by recursively extracting IFC data instances in referential relations directly from an IFC instance model file, and it relies solely on the internal data structure of an IFC instance model, without an IFC schema or a MVD. The algorithm extracts physical and nonphysical data instances relevant to the user's selection of building elements by recursively iterating through data instances based on the rules specified in the algorithm. A set of required building elements is not defined on the spot; rather, a set of building elements required for a specific process is predefined as part of an information delivery manual (IDM) and can be used as input. The algorithm was tested by extracting partial models from 32 IFC 2x3 test casesinitially developed to evaluate the IFC compliancy of software applications in the construction industryand from an actual BIM project. The integrity of the extracted partial models was first validated by checking the syntax against an IFC schema and by checking the semantics of partial models using two IFC validators, namely, the Express Engine and the IfcObjectCounter. Test results showed that the proposed algorithm successfully extracts the intended partial models from the IFC instance files without using a schema. (C) 2013 American Society of Civil Engineers.