Explanation/Reference:
The topology data model of Oracle Spatial lets you work with data about nodes, edges, and faces in a topology.
A node, represented by a point, can be isolated or it can be used to bound edges An edge is bounded by two nodes: the start (origin) node and the end (terminal) node.
The start node of the positive directed edge is the end node of the negative directed edge. An edge also lies between two faces and has references to both of them. Each directed edge contains a reference to the next edge in the contiguous perimeter of the face on its left side. A face, corresponding to a polygon, has a reference to one directed edge of its outer boundary. If any island nodes or island edges are present, the face also has a reference to one directed edge on the boundary of each island. Examples of geographic entities that might be represented as faces include parks, lakes, counties, and states.
References: https://docs.oracle.com/cd/B19306_01/appdev.102/b14256/sdo_topo_concepts.htm