+
+/* returns pointer to state if OK, otherwise NULL */
+typedef gpointer (*VikDataSourceInitFunc) ();
+
+/* returns NULL if OK, otherwise returns an error message. */
+typedef gchar *(*VikDataSourceCheckExistenceFunc) ();
+
+/* Create widgets to show in a setup dialog, set up state via user_data */
+typedef void (*VikDataSourceAddSetupWidgetsFunc) ( GtkWidget *dialog, VikViewport *vvp, gpointer user_data );