Consider an <Areal Feature> instance L representing an environmental object classified as ECC_LAKE. The topology of L is represented by a regular <Feature Face> instance, the outer boundary of which is defined by two <Feature Edge> instances, one defining the north shore of the lake, the other defining the south shore.
To indicate that these two <Feature Edge> instances define the outer boundary of the lake, each is a component of an external <Feature Face Ring> instance through an <Edge Direction> link object that indicates its orientation with respect to the <Feature Face Ring> instance. The <Feature Face Ring> instance is in turn a component of the <Feature Face> instance specifying the topology of L. These relationships are depicted in Figure 6.16:
