Editing Industry Foundation Classes (section)

===Products===
IfcProduct is the base class for all physical objects and is subdivided into spatial elements, physical elements, structural analysis items, and other concepts.  Products may have associated materials, shape representations, and placement in space.  Spatial elements include IfcSite, IfcBuilding, IfcBuildingStorey, and IfcSpace.  Physical building elements include IfcWall, IfcBeam, IfcDoor, IfcWindow, IfcStair, etc.  Distribution elements ([[HVAC]], [[electrical]], [[plumbing]]) have a concept of ports where elements may have specific connections for various services, and connected together using cables, pipes, or ducts to form a system.  Various connectivity relationships are used for building elements such as walls having openings filled by doors or windows.

Materials may be defined for products as a whole, or as layers, profiles, or constituents for specified parts.
* IfcMaterial indicates a specific material, with optional properties (e.g. mechanical, thermal) and styles (e.g. colors, textures).
* IfcMaterialLayerSet captures a list of layers, each indicating a material of a specified thickness.
* IfcMaterialProfileSet [IFC2x4] captures a set of profiles, each indicating a material of a specified cross-section.
* IfcMaterialConstituentSet [IFC2x4] captures a set of constituents, each indicating a material used at a named shape aspect.

Representations may be defined for explicit 3D shape, and optionally as parametric constraints.  Each representation is identified by IfcShapeRepresentation with a well-known name. 
* 'Body' indicates a 3D shape which may be represented by [[B-rep]], [[NURBS]], [[Constructive Solid Geometry]] (CSG), or swept profiles.  It may be defined directly or derived by applying material definitions to other representations.
* 'Axis' indicates a path for linear elements (e.g. wall, beam, pipe) for which material profiles or layers are aligned.
* 'FootPrint' indicates a boundary for planar elements (e.g. slab, staircase) for which material layers are bounded.
* 'Profile' indicates a side profile for opening elements (e.g. door, window) for which material constituents are bounded.
* 'SurveyPoints' indicates a set of points for surface elements (e.g. site) for describing contours.

Placement may indicate position, vertical angle, and horizontal angle.
* IfcLocalPlacement indicates placement relative to an enclosing element hierarchy.
* IfcGridPlacement indicates placement relative to a grid with user-defined axes.

Quantities may be defined for take-off purposes such as Gross Area, Gross Volume, Gross Weight, Net Weight, etc.  IFC defines various quantities specific to each element type and the method of calculation according to geometry and relationships.