diff --git a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedJobUsageRecord.java b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedJobUsageRecord.java
index 7b6990e..e1ae95b 100644
--- a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedJobUsageRecord.java
+++ b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedJobUsageRecord.java
@@ -6,7 +6,6 @@ package org.gcube.accounting.datamodel.aggregation;
 import java.io.Serializable;
 import java.util.Calendar;
 import java.util.Map;
-import java.util.Set;
 
 import org.gcube.accounting.datamodel.AggregatedUsageRecord;
 import org.gcube.accounting.datamodel.basetypes.AbstractJobUsageRecord;
@@ -39,11 +38,6 @@ public class AggregatedJobUsageRecord extends AbstractJobUsageRecord implements
 		throw new UnsupportedOperationException();
 	}
 	
-	@Override
-	public Set<String> getAggregatedFields() {
-		return aggregatedFields;
-	}
-	
 	@Override
 	public int getOperationCount() {
 		return super.getOperationCount();
diff --git a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedPortletUsageRecord.java b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedPortletUsageRecord.java
index bfbe67d..139747c 100644
--- a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedPortletUsageRecord.java
+++ b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedPortletUsageRecord.java
@@ -6,7 +6,6 @@ package org.gcube.accounting.datamodel.aggregation;
 import java.io.Serializable;
 import java.util.Calendar;
 import java.util.Map;
-import java.util.Set;
 
 import org.gcube.accounting.datamodel.AggregatedUsageRecord;
 import org.gcube.accounting.datamodel.basetypes.AbstractPortletUsageRecord;
@@ -40,11 +39,6 @@ public class AggregatedPortletUsageRecord extends AbstractPortletUsageRecord imp
 		throw new UnsupportedOperationException();
 	}
 
-	@Override
-	public Set<String> getAggregatedFields() {
-		return aggregatedFields;
-	}
-	
 	@Override
 	public int getOperationCount() {
 		return super.getOperationCount();
diff --git a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedServiceUsageRecord.java b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedServiceUsageRecord.java
index 89eb0a5..2c75fe3 100644
--- a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedServiceUsageRecord.java
+++ b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedServiceUsageRecord.java
@@ -6,7 +6,6 @@ package org.gcube.accounting.datamodel.aggregation;
 import java.io.Serializable;
 import java.util.Calendar;
 import java.util.Map;
-import java.util.Set;
 
 import org.gcube.accounting.datamodel.AggregatedUsageRecord;
 import org.gcube.accounting.datamodel.basetypes.AbstractServiceUsageRecord;
@@ -57,11 +56,6 @@ public class AggregatedServiceUsageRecord extends AbstractServiceUsageRecord imp
 		this.setEndTime(creationTime);
 	}
 	
-	@Override
-	public Set<String> getAggregatedFields() {
-		return aggregatedFields;
-	}
-	
 	@Override
 	public int getOperationCount() {
 		return super.getOperationCount();
diff --git a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedStorageUsageRecord.java b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedStorageUsageRecord.java
index 8d69317..ccd50ab 100644
--- a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedStorageUsageRecord.java
+++ b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedStorageUsageRecord.java
@@ -6,7 +6,6 @@ package org.gcube.accounting.datamodel.aggregation;
 import java.io.Serializable;
 import java.util.Calendar;
 import java.util.Map;
-import java.util.Set;
 
 import org.gcube.accounting.datamodel.AggregatedUsageRecord;
 import org.gcube.accounting.datamodel.basetypes.AbstractStorageUsageRecord;
@@ -48,11 +47,6 @@ public class AggregatedStorageUsageRecord extends AbstractStorageUsageRecord imp
 		this.setEndTime(creationTime);
 	}
 	
-	@Override
-	public Set<String> getAggregatedFields() {
-		return aggregatedFields;
-	}
-	
 	@Override
 	public int getOperationCount() {
 		return super.getOperationCount();
diff --git a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedTaskUsageRecord.java b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedTaskUsageRecord.java
index ed1a8d2..0fcb95d 100644
--- a/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedTaskUsageRecord.java
+++ b/src/main/java/org/gcube/accounting/datamodel/aggregation/AggregatedTaskUsageRecord.java
@@ -6,7 +6,6 @@ package org.gcube.accounting.datamodel.aggregation;
 import java.io.Serializable;
 import java.util.Calendar;
 import java.util.Map;
-import java.util.Set;
 
 import org.gcube.accounting.datamodel.AggregatedUsageRecord;
 import org.gcube.accounting.datamodel.basetypes.AbstractTaskUsageRecord;
@@ -39,12 +38,6 @@ public class AggregatedTaskUsageRecord extends AbstractTaskUsageRecord implement
 		throw new UnsupportedOperationException();
 	}
 	
-
-	@Override
-	public Set<String> getAggregatedFields() {
-		return aggregatedFields;
-	}
-	
 	@Override
 	public int getOperationCount() {
 		return super.getOperationCount();
diff --git a/src/main/java/org/gcube/accounting/datamodel/basetypes/AbstractJobUsageRecord.java b/src/main/java/org/gcube/accounting/datamodel/basetypes/AbstractJobUsageRecord.java
index ca34abd..4f882aa 100644
--- a/src/main/java/org/gcube/accounting/datamodel/basetypes/AbstractJobUsageRecord.java
+++ b/src/main/java/org/gcube/accounting/datamodel/basetypes/AbstractJobUsageRecord.java
@@ -34,14 +34,13 @@ public abstract class AbstractJobUsageRecord extends BasicUsageRecord {
 	@NotEmptyIfNotNull
 	public static final String JOB_QUALIFIER = "jobQualifier";
 	
-	@RequiredField @ValidLong
+	@ValidLong
 	public static final String JOB_START_TIME = "jobStartTime";
-	@RequiredField @ValidLong
+	@ValidLong
 	public static final String JOB_END_TIME = "jobEndTime";
-	@ComputedField(action=CalculateJobWallDurationAction.class) @ValidLong
+	@RequiredField @ComputedField(action=CalculateJobWallDurationAction.class) @ValidLong
 	public static final String WALL_DURATION = "_wallDuration";
 	
-	
 	public AbstractJobUsageRecord(){
 		super();
 	}
diff --git a/src/main/java/org/gcube/accounting/datamodel/basetypes/AbstractTaskUsageRecord.java b/src/main/java/org/gcube/accounting/datamodel/basetypes/AbstractTaskUsageRecord.java
index 5af5361..ec7791f 100644
--- a/src/main/java/org/gcube/accounting/datamodel/basetypes/AbstractTaskUsageRecord.java
+++ b/src/main/java/org/gcube/accounting/datamodel/basetypes/AbstractTaskUsageRecord.java
@@ -37,13 +37,15 @@ public abstract class AbstractTaskUsageRecord extends BasicUsageRecord {
 	@NotEmptyIfNotNull
 	public static final String REF_HOSTING_NODE_ID = "refHostingNodeId";
 	
-	@RequiredField @ValidLong
+	@ValidLong
 	public static final String TASK_START_TIME = "taskStartTime";
-	@RequiredField @ValidLong
+	@ValidLong
 	public static final String TASK_END_TIME = "taskEndTime";
-	@ComputedField(action=CalculateTaskWallDurationAction.class) @ValidLong
+	@RequiredField @ComputedField(action=CalculateTaskWallDurationAction.class) @ValidLong
 	public static final String WALL_DURATION = "_wallDuration";
 	
+	
+	
 	@NotEmptyIfNotNull
 	public static final String INPUT_PARAMETERS = "inputParameters";
 	
@@ -118,7 +120,6 @@ public abstract class AbstractTaskUsageRecord extends BasicUsageRecord {
 
 	public void setTaskStartTime(Calendar startTime) throws InvalidValueException {
 		setResourceProperty(TASK_START_TIME, startTime.getTimeInMillis());
-		
 	}
 
 	public Calendar getTaskEndTime() {
diff --git a/src/test/java/org/gcube/accounting/datamodel/usagerecords/JobUsageRecordTest.java b/src/test/java/org/gcube/accounting/datamodel/usagerecords/JobUsageRecordTest.java
index c5084b4..9895afb 100644
--- a/src/test/java/org/gcube/accounting/datamodel/usagerecords/JobUsageRecordTest.java
+++ b/src/test/java/org/gcube/accounting/datamodel/usagerecords/JobUsageRecordTest.java
@@ -34,8 +34,7 @@ public class JobUsageRecordTest extends ScopedTest {
 		expectedRequiredFields.add(UsageRecord.SCOPE);
 		expectedRequiredFields.add(UsageRecord.OPERATION_RESULT);
 		expectedRequiredFields.add(AbstractJobUsageRecord.JOB_ID);
-		expectedRequiredFields.add(AbstractJobUsageRecord.JOB_START_TIME);
-		expectedRequiredFields.add(AbstractJobUsageRecord.JOB_END_TIME);
+		expectedRequiredFields.add(AbstractJobUsageRecord.WALL_DURATION);
 		return expectedRequiredFields;
 	}
 	
diff --git a/src/test/java/org/gcube/accounting/datamodel/usagerecords/TaskUsageRecordTest.java b/src/test/java/org/gcube/accounting/datamodel/usagerecords/TaskUsageRecordTest.java
index 3eb8772..61b275c 100644
--- a/src/test/java/org/gcube/accounting/datamodel/usagerecords/TaskUsageRecordTest.java
+++ b/src/test/java/org/gcube/accounting/datamodel/usagerecords/TaskUsageRecordTest.java
@@ -34,9 +34,7 @@ public class TaskUsageRecordTest extends ScopedTest {
 		expectedRequiredFields.add(UsageRecord.SCOPE);
 		expectedRequiredFields.add(UsageRecord.OPERATION_RESULT);
 		expectedRequiredFields.add(AbstractTaskUsageRecord.TASK_ID);
-		expectedRequiredFields.add(AbstractTaskUsageRecord.TASK_START_TIME);
-		expectedRequiredFields.add(AbstractTaskUsageRecord.TASK_END_TIME);
-		
+		expectedRequiredFields.add(AbstractTaskUsageRecord.WALL_DURATION);
 		return expectedRequiredFields;
 	}