Boundary Representation (B-Rep):

A boundary model or b-rep model is depending on the topological notion that a physical object is bounded by a set of faces. These faces are regions or subsets of closed and orientable surfaces.

Boundary Representation, or b-rep for short, may be considered as an extension to the wire-frame model. The merit of a b-rep is that a solid is bounded through its surface and contain its interior and exterior. The surface of a solid contains a set of well-organized faces, each of that is a piece of some surface (for example. a surface patch). Faces might share vertices and edges that are curve segments. Thus, a b-rep is an extension to the wire-frame model by summing face information to the latter. The geometry of the object may be described by its boundaries, say vertices, edges and surfaces. An instance of b-rep is shown in Figure. A closed surface is one that is continuous without breaks. An orient able surface is one in which this is possible to distinguish two sides using the direction of the surface normal to point to the inside or outside of the solid model under construction.

Each of the face is bounded by edges and each edge is bounded by vertices. Therefore, topologically, a boundary model of an object is consisted of faces, edges, & vertices of the object connected together in such a way as to ensure the topological constancy of the model.