BOM (Bill Of Materials) Manager is a service class that works with BOM tables, part references and BOM rows. All data held by BOM tables is stored in data containers that call data entries. There are three data entry types: DataEntry, DataEntryPart, and DataEntryBlock. DataEntryPart is connected with part references, and DataEntryBlock is connected with components.
Complex graphic scenes with a large number of elements are sometimes drawn slowly. In this case, dynamic graphic elements (such as cursors, grip/snap points, selection rectangles, user interface elements, and so on) are drawn slowly too because to correctly combine graphic scenes and dynamic graphic elements, the renderer must redraw all underlying scene elements.
Many elements in Teigha BIM contain B-Rep geometries in GElement, which is a geometry cache of an element. However, B-Rep is not a universal format. Each product has a specific representation of B-Reps.
An overview of B-Reps and BIM specifics can be found in the documentation (login required).