th actual vertex objects, but rather with <i>vertex
descriptors</i>. Many graph representations (such as adjacency lists) do not
store actual vertex objects, while others do (e.g., pointer-linked graphs). This
difference is hidden underneath the &quot;black-box&quot; of the vertex
descriptor object. The vertex descriptor is something provided by each graph
type that can be used to access information about the graph via the <tt>out_edges()</tt>,
<tt>in_edges()</tt>, <tt>adjacent_vertices()</tt>, and property