diff --git a/examples/Data/randomGrid3D.xml b/examples/Data/randomGrid3D.xml
index 42eb473be..233ad4ad7 100644
--- a/examples/Data/randomGrid3D.xml
+++ b/examples/Data/randomGrid3D.xml
@@ -1,13 +1,13 @@
 <?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
 <!DOCTYPE boost_serialization>
-<boost_serialization signature="serialization::archive" version="17">
-<graph class_id="0" tracking_level="0" version="0">
+<boost_serialization signature="serialization::archive" version="19">
+<data class_id="0" tracking_level="0" version="0">
 	<Base class_id="1" tracking_level="0" version="0">
 		<factors_ class_id="2" tracking_level="0" version="0">
 			<count>32</count>
 			<item_version>1</item_version>
 			<item class_id="3" tracking_level="0" version="1">
-				<px class_id="4" class_name="gtsam::JacobianFactor" tracking_level="1" version="0" object_id="_0">
+				<px class_id="4" class_name="gtsam::JacobianFactor" tracking_level="1" version="1" object_id="_0">
 					<Base class_id="5" tracking_level="0" version="0">
 						<Base class_id="6" tracking_level="0" version="0">
 							<keys_>
@@ -100,9 +100,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_ class_id="11" tracking_level="0" version="1">
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -199,9 +197,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -298,9 +294,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -397,9 +391,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -496,9 +488,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -595,9 +585,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -694,9 +682,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -793,9 +779,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -892,9 +876,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -991,9 +973,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1090,9 +1070,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1189,9 +1167,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1288,9 +1264,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1387,9 +1361,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1486,9 +1458,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1585,9 +1555,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1684,9 +1652,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1783,9 +1749,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1882,9 +1846,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -1981,9 +1943,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2080,9 +2040,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2179,9 +2137,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2278,9 +2234,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2377,9 +2331,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2476,9 +2428,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2575,9 +2525,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2674,9 +2622,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2773,9 +2719,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2872,9 +2816,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -2971,9 +2913,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -3070,9 +3010,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -3402,13 +3340,11 @@
 						<rowEnd_>3</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 		</factors_>
 	</Base>
-</graph>
+</data>
 </boost_serialization>
 
diff --git a/examples/Data/toy3D.xml b/examples/Data/toy3D.xml
index 26bd231ca..acc2bbe3c 100644
--- a/examples/Data/toy3D.xml
+++ b/examples/Data/toy3D.xml
@@ -1,13 +1,13 @@
 <?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
 <!DOCTYPE boost_serialization>
-<boost_serialization signature="serialization::archive" version="17">
-<graph class_id="0" tracking_level="0" version="0">
+<boost_serialization signature="serialization::archive" version="19">
+<data class_id="0" tracking_level="0" version="0">
 	<Base class_id="1" tracking_level="0" version="0">
 		<factors_ class_id="2" tracking_level="0" version="0">
 			<count>2</count>
 			<item_version>1</item_version>
 			<item class_id="3" tracking_level="0" version="1">
-				<px class_id="4" class_name="gtsam::JacobianFactor" tracking_level="1" version="0" object_id="_0">
+				<px class_id="4" class_name="gtsam::JacobianFactor" tracking_level="1" version="1" object_id="_0">
 					<Base class_id="5" tracking_level="0" version="0">
 						<Base class_id="6" tracking_level="0" version="0">
 							<keys_>
@@ -100,9 +100,7 @@
 						<rowEnd_>9</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_ class_id="11" tracking_level="0" version="1">
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 			<item>
@@ -157,13 +155,11 @@
 						<rowEnd_>3</rowEnd_>
 						<blockStart_>0</blockStart_>
 					</Ab_>
-					<model_>
-						<px class_id="-1"></px>
-					</model_>
+					<model_null>1</model_null>
 				</px>
 			</item>
 		</factors_>
 	</Base>
-</graph>
+</data>
 </boost_serialization>