diff --git a/src/common/graph.ts b/src/common/graph.ts
index 3052e6446cb6ce20d78c2301f2dc2d86333b3459..f8463159eec1eb94baf2c143ff77c4049e859d07 100644
--- a/src/common/graph.ts
+++ b/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[];