Basic graph content interface

src/common/graph.ts

@@ -46,10 +46,16 @@ export interface Coordinate {
     z: number;
 }
 
+export interface GraphContent {
+    nodes: Node[];
+    links: Link[];
+    objectGroups: GraphObjectType[];
+}
+
 /**
  * Basic graph data structure.
  */
-export default class Graph {
+export default class Graph implements GraphContent {
     public nodes: Node[];
     public links: Link[];
     public objectGroups: GraphObjectType[];