diff --git a/src/main/java/org/gcube/informationsystem/resourceregistry/contexts/entities/ContextManagement.java b/src/main/java/org/gcube/informationsystem/resourceregistry/contexts/entities/ContextManagement.java
index 4045545..35c757b 100644
--- a/src/main/java/org/gcube/informationsystem/resourceregistry/contexts/entities/ContextManagement.java
+++ b/src/main/java/org/gcube/informationsystem/resourceregistry/contexts/entities/ContextManagement.java
@@ -142,13 +142,13 @@ public class ContextManagement extends EntityElementManagement<Context, EntityTy
 			select.append(parentId);
 			select.append(" MAXDEPTH 1) WHERE ");
 			select.append(Context.NAME_PROPERTY);
-			select.append(ConditionalOperator.EQ.getConditionalOperator());
+			select.append(ConditionalOperator.EQ.getDbConditionalOperator());
 			select.append("\"");
 			select.append(getName());
 			select.append("\"");
 			select.append(LogicalOperator.AND.getLogicalOperator());
 			select.append(IdentifiableElement.ID_PROPERTY);
-			select.append(ConditionalOperator.NE.getConditionalOperator());
+			select.append(ConditionalOperator.NE.getDbConditionalOperator());
 			select.append("\"");
 			select.append(parentContext.uuid);
 			select.append("\"");
@@ -164,7 +164,7 @@ public class ContextManagement extends EntityElementManagement<Context, EntityTy
 			select.append(Context.NAME);
 			select.append(" WHERE ");
 			select.append(Context.NAME_PROPERTY);
-			select.append(ConditionalOperator.EQ.getConditionalOperator());
+			select.append(ConditionalOperator.EQ.getDbConditionalOperator());
 			select.append("\"");
 			select.append(getName());
 			select.append("\"");
diff --git a/src/main/java/org/gcube/informationsystem/resourceregistry/queries/json/base/JsonQueryERElement.java b/src/main/java/org/gcube/informationsystem/resourceregistry/queries/json/base/JsonQueryERElement.java
index 5176bd3..5b09b52 100644
--- a/src/main/java/org/gcube/informationsystem/resourceregistry/queries/json/base/JsonQueryERElement.java
+++ b/src/main/java/org/gcube/informationsystem/resourceregistry/queries/json/base/JsonQueryERElement.java
@@ -327,9 +327,9 @@ public abstract class JsonQueryERElement {
 				throw new UnsupportedOperationException();
 			}
 			
-			StringBuffer key = getKey(null, fieldNamePrefix);
-			StringBuffer value = getValue(jsonNode);
-			stringBuffer.append(addCondition(queryConditionalOperator, key, value));
+			String key = getKey(null, fieldNamePrefix);
+			String value = getValue(jsonNode);
+			stringBuffer.append(queryConditionalOperator.addCondition(key, value));
 			return stringBuffer;
 		}
 		
@@ -351,43 +351,34 @@ public abstract class JsonQueryERElement {
 		}
 		
 		if(jsonNode.isTextual() || jsonNode.isNumber()) {
-			StringBuffer key = getKey(fieldName, fieldNamePrefix);
-			StringBuffer value = getValue(jsonNode);
-			stringBuffer.append(addCondition(ConditionalOperator.EQ, key, value));
+			String key = getKey(fieldName, fieldNamePrefix);
+			String value = getValue(jsonNode);
+			stringBuffer.append(ConditionalOperator.EQ.addCondition(key, value));
 		}
 		
 		if(jsonNode.isNull()) {
-			StringBuffer key = getKey(fieldName, null);
-			stringBuffer.append(addCondition(ConditionalOperator.IS, key, null));
+			String key = getKey(fieldName, null);
+			stringBuffer.append(ConditionalOperator.IS.addCondition(key, null));
 		}
 		
 		return stringBuffer;
 	}
 	
-	protected StringBuffer addCondition(ConditionalOperator queryConditionalOperator, StringBuffer key, StringBuffer value) {
-		StringBuffer stringBuffer = new StringBuffer();
-		stringBuffer.append(key);
-		stringBuffer.append(queryConditionalOperator.getConditionalOperator());
-		stringBuffer.append(value);
-		return stringBuffer;
-	}
-	
-	
-	protected StringBuffer getKey(String fieldName, String fieldNamePrefix) {
+	protected String getKey(String fieldName, String fieldNamePrefix) {
 		StringBuffer stringBuffer = new StringBuffer();
 		if(fieldNamePrefix!=null) {
-			stringBuffer.append(fieldNamePrefix);
-			if(fieldName!=null && fieldName.compareTo("")!=0) {
+			stringBuffer.append(fieldNamePrefix.trim());
+			if(fieldName!=null && fieldName.trim().length()==0) {
 				stringBuffer.append(".");
 			}
 		}
 		if(fieldName!=null) {
-			stringBuffer.append(fieldName);
+			stringBuffer.append(fieldName.trim());
 		}
-		return stringBuffer;
+		return stringBuffer.toString();
 	}
 	
-	protected StringBuffer getValue(JsonNode jsonNode) {
+	protected String getValue(JsonNode jsonNode) {
 		StringBuffer stringBuffer = new StringBuffer();
 		
 		String value = jsonNode.asText();
@@ -398,7 +389,7 @@ public abstract class JsonQueryERElement {
 			stringBuffer.append(value);
 			stringBuffer.append("\"");
 		}
-		return stringBuffer;
+		return stringBuffer.toString();
 	}
 	
 	protected List<JsonQueryERElement> getChildrenBreadcrumb() {
diff --git a/src/main/java/org/gcube/informationsystem/resourceregistry/queries/operators/ConditionalOperator.java b/src/main/java/org/gcube/informationsystem/resourceregistry/queries/operators/ConditionalOperator.java
index aef9f1d..0711918 100644
--- a/src/main/java/org/gcube/informationsystem/resourceregistry/queries/operators/ConditionalOperator.java
+++ b/src/main/java/org/gcube/informationsystem/resourceregistry/queries/operators/ConditionalOperator.java
@@ -41,24 +41,24 @@ public enum ConditionalOperator {
 	IS_DEFINED("_isDefined", " IS DEFINED ", BaseTypeGroup.ANY, "Returns TRUE is a field is defined in a document"),
 	IS_NOT_DEFINED("_isNotDefined", " IS NOT DEFINED ", BaseTypeGroup.ANY, "Returns TRUE is a field is not defined in a document");
 	
-	protected final String operator;
-	protected final String conditionalOperator;
+	protected final String operatorKey;
+	protected final String dbConditionalOperator;
 	protected final BaseTypeGroup allowed;
 	protected final String description;
 	
-	private ConditionalOperator(String operator, String conditionalOperator, BaseTypeGroup allowed, String description) {
-		this.operator = operator;
-		this.conditionalOperator = conditionalOperator;
+	private ConditionalOperator(String operatorKey, String conditionalOperator, BaseTypeGroup allowed, String description) {
+		this.operatorKey = operatorKey;
+		this.dbConditionalOperator = conditionalOperator;
 		this.allowed = allowed;
 		this.description = description;
 	}
 	
-	public String getOperator() {
-		return operator;
+	protected String getOperatorKey() {
+		return operatorKey;
 	}
 	
-	public String getConditionalOperator() {
-		return conditionalOperator;
+	public String getDbConditionalOperator() {
+		return dbConditionalOperator;
 	}
 
 	public String getDescription() {
@@ -73,8 +73,8 @@ public enum ConditionalOperator {
 		ConditionalOperator.operatorByKey = new HashMap<>();
 		
 		for(ConditionalOperator queryComparisonOperator : ConditionalOperator.values()) {
-			ConditionalOperator.operators.add(queryComparisonOperator.getOperator());
-			ConditionalOperator.operatorByKey.put(queryComparisonOperator.getOperator(), queryComparisonOperator);
+			ConditionalOperator.operators.add(queryComparisonOperator.getOperatorKey());
+			ConditionalOperator.operatorByKey.put(queryComparisonOperator.getOperatorKey(), queryComparisonOperator);
 		}
 	}
 	
@@ -85,4 +85,12 @@ public enum ConditionalOperator {
 	public static ConditionalOperator getQueryComparisonOperator(String key) {
 		return operatorByKey.get(key);
 	}
+	
+	public StringBuffer addCondition(String key, String value) {
+		StringBuffer stringBuffer = new StringBuffer();
+		stringBuffer.append(key);
+		stringBuffer.append(getDbConditionalOperator());
+		stringBuffer.append(value);
+		return stringBuffer;
+	}
 }
diff --git a/src/main/java/org/gcube/informationsystem/resourceregistry/queries/operators/MatemathicsOperator.java b/src/main/java/org/gcube/informationsystem/resourceregistry/queries/operators/MatemathicsOperator.java
index fc38e30..dc41379 100644
--- a/src/main/java/org/gcube/informationsystem/resourceregistry/queries/operators/MatemathicsOperator.java
+++ b/src/main/java/org/gcube/informationsystem/resourceregistry/queries/operators/MatemathicsOperator.java
@@ -1,7 +1,6 @@
 package org.gcube.informationsystem.resourceregistry.queries.operators;
 
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 
@@ -48,39 +47,41 @@ public enum MatemathicsOperator {
 	public static final String AS_KEY = "as";
 	
 	protected final String operatorKey;
-	protected final String dbQueryOperator;
+	protected final String dbMatemathicsOperator;
 	protected final String description;
 	
-	private MatemathicsOperator(String operatorKey, String dbQueryOperator, String description) {
+	private MatemathicsOperator(String operatorKey, String dbMatemathicsOperator, String description) {
 		this.operatorKey = operatorKey;
-		this.dbQueryOperator = dbQueryOperator;
+		this.dbMatemathicsOperator = dbMatemathicsOperator;
 		this.description = description;
 	}
 	
-	public String getOperatorKey() {
+	protected String getOperatorKey() {
 		return operatorKey;
 	}
 	
-	public String getDbQueryOperator() {
-		return dbQueryOperator;
+	protected String getDbMatemathicsOperator() {
+		return dbMatemathicsOperator;
 	}
 
 	public String getDescription() {
 		return description;
 	}
 
+	private static Set<String> operators;
 	private static Map<String,MatemathicsOperator> operatorByKey;
 	
 	static {
 		MatemathicsOperator.operatorByKey = new HashMap<>();
 		
 		for(MatemathicsOperator matemathicsOperator : MatemathicsOperator.values()) {
+			MatemathicsOperator.operators.add(matemathicsOperator.getOperatorKey());
 			MatemathicsOperator.operatorByKey.put(matemathicsOperator.getOperatorKey(), matemathicsOperator);
 		}
 	}
 	
 	public static Set<String> getOperators() {
-		return new HashSet<>(MatemathicsOperator.operatorByKey.keySet());
+		return operators;
 	}
 	
 	public static MatemathicsOperator getMatemathicsOperator(String key) {
@@ -160,13 +161,13 @@ public enum MatemathicsOperator {
 			
 			if(i<(size-1)) {
 				buffer.append(" ");
-				buffer.append(dbQueryOperator);
+				buffer.append(dbMatemathicsOperator);
 				buffer.append(" ");
 				if(fieldsSeparator!=null) {
 					buffer.append("'");
 					buffer.append(fieldsSeparator);
 					buffer.append("' ");
-					buffer.append(dbQueryOperator);
+					buffer.append(dbMatemathicsOperator);
 					buffer.append(" ");
 				}
 			}