diff --git a/src/org/ntlab/deltaViewer/CollaborationLayout.java b/src/org/ntlab/deltaViewer/CollaborationLayout.java
index 45ea389..0f5ce73 100644
--- a/src/org/ntlab/deltaViewer/CollaborationLayout.java
+++ b/src/org/ntlab/deltaViewer/CollaborationLayout.java
@@ -27,7 +27,7 @@
 import com.mxgraph.util.mxPoint;
 
 public class CollaborationLayout implements IObjectLayout {
-	private static final int angleStep = 15;
+	private static final int angleStep = 30;
 	private mxPoint coordinatorPoint = new mxPoint(0, 100);
 	private double step;
 	private double padding;		
@@ -114,7 +114,12 @@
 					String dstObjId = methodExec.getReturnValue().getId();
 					String srcClassName = methodExec.getThisClassName();
 					String dstClassName = methodExec.getReturnValue().getActualType();
-					idx = references.indexOf(new Reference(srcObjId, dstObjId, srcClassName, dstClassName));
+					Reference r = new Reference(srcObjId, dstObjId, srcClassName, dstClassName);
+					idx = references.indexOf(r);
+					if (idx < 0) {
+						references.add(r);
+						idx = references.indexOf(r);
+					}
 				}
 			} else if (a.getAliasType() == AliasType.CONSTRACTOR_INVOCATION) {
 				MethodInvocation c = (MethodInvocation) a.getOccurrencePoint().getStatement();
diff --git a/src/org/ntlab/deltaViewer/CollaborationViewer.java b/src/org/ntlab/deltaViewer/CollaborationViewer.java
index 1a7ce0f..2cfe039 100644
--- a/src/org/ntlab/deltaViewer/CollaborationViewer.java
+++ b/src/org/ntlab/deltaViewer/CollaborationViewer.java
@@ -414,8 +414,8 @@
 			}
 			for (Alias alias: aliasCollector.getAliasList()) {
 				if (alias.getAliasType() == Alias.AliasType.THIS) {
-					if (!objectToVertexMap.containsKey(alias.getObjectId())) {
-						// When both of the calling and called method are static.
+					if (!objectToVertexMap.containsKey(alias.getObjectId()) && alias.getMethodExecution().isStatic()) {
+						// When both of the calling and called methods are static.
 						String thisObjId = alias.getObjectId();
 						String thisClassName = alias.getMethodExecution().getThisClassName();
 						mxICell vertex = (mxICell) mxgraph.insertDeltaVertex(getMxDefaultParent(), thisObjId, thisClassName, 0, 0, objecVertexWidth, ObjectVertexHeight, "fillColor=white"); //creates a white vertex. 
@@ -428,7 +428,7 @@
 						thisObjId += ":" + thisClassName;
 					}
 					if (!objectToVertexMap.containsKey(thisObjId)) {
-						// When the called method are static.
+						// When the called method is static.
 						mxICell vertex = (mxICell) mxgraph.insertDeltaVertex(getMxDefaultParent(), thisObjId, thisClassName, 0, 0, objecVertexWidth, ObjectVertexHeight, "fillColor=white"); //creates a white vertex. 
 						objectToVertexMap.put(thisObjId, new ObjectVertex(thisClassName, vertex, 0, 0));
 					}
@@ -507,9 +507,9 @@
 							fieldName = nextAliasObjId;
 						}
 					}
-					if(statement != null && statement instanceof FieldAccess 
-							&& curAliasObjId.equals(((FieldAccess)statement).getContainerObjId())) { // Contains alias type of nextAlias is FIELD.
+					if (statement != null && statement instanceof FieldAccess) {
 						FieldAccess fieldAccess = (FieldAccess)statement;
+						String containerId = fieldAccess.getContainerObjId();
 						if (fieldAccess.getFieldName() != null) {
 							String fieldNames[] = formatFieldName(fieldAccess.getFieldName());
 							srcClassName = fieldNames[0];
@@ -518,6 +518,13 @@
 							srcClassName = fieldAccess.getContainerClassName();
 							fieldName = nextAliasObjId;
 						}
+						if (containerId.matches("0")) {
+							containerId = "0:" + srcClassName;
+						}
+						if  (!curAliasObjId.equals(containerId)) { // Contains alias type of nextAlias is FIELD.
+							srcClassName = null;
+							fieldName = null;
+						}
 					}
 				}
 				System.out.println(TAG + ": srcClassName=" + srcClassName + "(curObjectId=" + curAliasObjId + ") -- fieldName=" + fieldName + " --> " + "(nextObjectId" + nextAliasObjId + ")");