A GM_Ring is used to represent a single connected component of a GM_SurfaceBoundary. It consists of a number of references to GM_OrientableCurves connected in a cycle (an object whose boundary is empty). <br/>A GM_Ring is structurally similar to a GM_CompositeCurve in that the endPoint of each GM_OrientedCurve OrientableCurve in the sequence is the startPoint of the next GM_ OrientableCurve in the Sequence. Since the sequence is circular, there is no exception to this rule. Each ring, like all boundaries is a cycle and each ring is simple.<br/>GM_Ring:<br/>{isSimple() = TRUE}<br/>{isCycle() = TRUE}<br/><br/>NOTE Even though each GM_Ring is simple, the boundary need not be simple. The easiest case of this is where one of the interior rings of a surface is tangent to its exterior ring. Implementations may enforce stronger restrictions on the interaction of boundary elements.<br/>