diff --git a/ch.psi.fda.core/pom.xml b/ch.psi.fda.core/pom.xml
index bf1c71b..c400bcf 100644
--- a/ch.psi.fda.core/pom.xml
+++ b/ch.psi.fda.core/pom.xml
@@ -3,7 +3,7 @@
 	<modelVersion>4.0.0</modelVersion>
 	<groupId>ch.psi</groupId>
 	<artifactId>ch.psi.fda.core</artifactId>
-	<version>0.0.1-SNAPSHOT</version>
+	<version>0.0.2</version>
 
 	<dependencies>
 		<dependency>
diff --git a/ch.psi.fda.core/src/main/java/ch/psi/fda/edescriptor/EDescriptor.java b/ch.psi.fda.core/src/main/java/ch/psi/fda/edescriptor/EDescriptor.java
index 5109701..446489c 100644
--- a/ch.psi.fda.core/src/main/java/ch/psi/fda/edescriptor/EDescriptor.java
+++ b/ch.psi.fda.core/src/main/java/ch/psi/fda/edescriptor/EDescriptor.java
@@ -1,8 +1,13 @@
 package ch.psi.fda.edescriptor;
 
+import javax.xml.bind.annotation.XmlRootElement;
+import javax.xml.bind.annotation.XmlTransient;
+
 /**
  * Execution container descriptor
  */
+@XmlRootElement
+@XmlTransient
 public interface EDescriptor {
 
 }
diff --git a/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/MatrixPlot.java b/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/MatrixPlot.java
index 41b0f27..078f8d6 100644
--- a/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/MatrixPlot.java
+++ b/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/MatrixPlot.java
@@ -13,11 +13,11 @@ public class MatrixPlot extends Plot {
 	private List<Series> data = new ArrayList<>();
 	private Double minX;
 	private Double maxX;
-	private Double nX;
+	private Integer nX;
 	
 	private Double minY;
 	private Double maxY;
-	private Double nY;
+	private Integer nY;
 	
 	public MatrixPlot(){
 	}
@@ -48,10 +48,10 @@ public class MatrixPlot extends Plot {
 		this.maxX = maxX;
 	}
 	@XmlAttribute
-	public Double getnX() {
+	public Integer getnX() {
 		return nX;
 	}
-	public void setnX(Double nX) {
+	public void setnX(Integer nX) {
 		this.nX = nX;
 	}
 	@XmlAttribute
@@ -69,10 +69,10 @@ public class MatrixPlot extends Plot {
 		this.maxY = maxY;
 	}
 	@XmlAttribute
-	public Double getnY() {
+	public Integer getnY() {
 		return nY;
 	}
-	public void setnY(Double nY) {
+	public void setnY(Integer nY) {
 		this.nY = nY;
 	}
 }
diff --git a/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/VDescriptor.java b/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/VDescriptor.java
index 7637703..8026f2c 100644
--- a/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/VDescriptor.java
+++ b/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/VDescriptor.java
@@ -1,5 +1,6 @@
 package ch.psi.fda.vdescriptor;
 
+import java.util.ArrayList;
 import java.util.List;
 
 import javax.xml.bind.annotation.XmlElement;
@@ -10,7 +11,7 @@ import javax.xml.bind.annotation.XmlRootElement;
 @XmlRootElement(name="vdescriptor")
 public class VDescriptor {
 	
-	private List<Plot> plots;
+	private List<Plot> plots = new ArrayList<>();
 
 	@XmlElementWrapper
 	@XmlElements({
diff --git a/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/XYZSeries.java b/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/XYZSeries.java
index e09d819..520f5cc 100644
--- a/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/XYZSeries.java
+++ b/ch.psi.fda.core/src/main/java/ch/psi/fda/vdescriptor/XYZSeries.java
@@ -13,11 +13,6 @@ public class XYZSeries extends Series {
 	public XYZSeries(){
 	}
 	
-	public XYZSeries(String x, String y){
-		this.x = x;
-		this.y = y;
-	}
-	
 	public XYZSeries(String x, String y, String z){
 		this.x = x;
 		this.y = y;