         return nil
     }
     
-
-    
-    public func update(_ aRelationship: Relationship) {
-        // TODO
-    }
+     //MARK: - Persistent
     
 
-    public func readXMLFile() throws {
+    func readXMLFile() throws {
         
         //var error : NSError?
         

    
    //MARK: - Node
    
    public func register(_ aNode: Node) {
    }
    
    public func update(_ aNode: Node) {
        // TODO
    }
    
    public func delete(_ aNode: Node) {
        // TODO
    }
    
    //MARK: - Relationship
    
    public func register(_ aRelationship: Relationship) {
        // TODO
    }
    
    public func delete(_ aRelationship: Relationship) {
        // TODO
    }
    
    public func findRelationship(from startNode: Node, to endNode: Node) -> Relationship?{

        }
    }
    
    /**
    
    func writeXMLFile() throws {
        
        // writeHeader
        
        // writeNodes
        for node in nodeList {
            write(node: Node, to: FileWrapper)
        }
    
        // writeFooter
    }
    
    func write(node: Node, to fileWrapper: FileWrapper)
 
    */
    
}
