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 b4b3a7f..5176bd3 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
@@ -22,6 +22,7 @@ import org.gcube.informationsystem.resourceregistry.api.exceptions.types.SchemaE
 import org.gcube.informationsystem.resourceregistry.api.exceptions.types.SchemaNotFoundException;
 import org.gcube.informationsystem.resourceregistry.queries.operators.ConditionalOperator;
 import org.gcube.informationsystem.resourceregistry.queries.operators.LogicalOperator;
+import org.gcube.informationsystem.resourceregistry.queries.operators.MatemathicsOperator;
 import org.gcube.informationsystem.resourceregistry.queries.operators.ProjectionOperator;
 import org.gcube.informationsystem.resourceregistry.types.TypesCache;
 import org.gcube.informationsystem.utils.TypeUtility;
@@ -187,10 +188,10 @@ public abstract class JsonQueryERElement {
 	protected StringBuffer generateAlias() {
 		StringBuffer sb = new StringBuffer();
 		sb.append(type.toLowerCase());
-		
-		// The entry point will have 00 as suffix
-		sb.append(breadcrumb.size());
-		sb.append(position);
+		for(JsonQueryERElement elem : breadcrumb) {
+			sb.append(elem.getPosition());
+		}
+		sb.append(this.position);
 		return sb;
 	}
 	
@@ -243,13 +244,11 @@ public abstract class JsonQueryERElement {
 				JsonNode node = objectNode.get(fieldName);
 				StringBuffer evBuffer = evaluateNode(node, fieldName, fieldNamePrefix);
 				
-				if(!first) {
-					stringBuffer.append(queryLogicalOperator.getLogicalOperator());
-				}
-				
 				if(evBuffer!=null && evBuffer.length()>0) {
 					if(first) {
 						first = false;
+					}else {
+						stringBuffer.append(queryLogicalOperator.getLogicalOperator());
 					}
 					stringBuffer.append(evBuffer);
 				}
@@ -293,13 +292,23 @@ public abstract class JsonQueryERElement {
 				b.append(getAlias(true));
 				b.append(".");
 				b.append(fieldNameToEmit);
-				b.append(" AS ");
+				b.append(" AS `");
 				b.append(nameOfFieldToEmit);
+				b.append("`");
 				addFieldToEmit(b.toString());
 			}
 			return null;
 		}
 		
+		if(MatemathicsOperator.getOperators().contains(fieldName)) {
+			--size;
+			setProjection(true);
+			MatemathicsOperator mo = MatemathicsOperator.getMatemathicsOperator(fieldName);
+			String fieldToEmit = mo.generateFieldToEmit(jsonNode, getAlias(true));
+			addFieldToEmit(fieldToEmit);
+			return null;
+		}
+		
 		
 		StringBuffer stringBuffer = new StringBuffer();
 		
@@ -347,6 +356,11 @@ public abstract class JsonQueryERElement {
 			stringBuffer.append(addCondition(ConditionalOperator.EQ, key, value));
 		}
 		
+		if(jsonNode.isNull()) {
+			StringBuffer key = getKey(fieldName, null);
+			stringBuffer.append(addCondition(ConditionalOperator.IS, key, null));
+		}
+		
 		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 2dc2ab5..fc38e30 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
@@ -5,6 +5,15 @@ import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 
+import javax.ws.rs.BadRequestException;
+
+import org.gcube.com.fasterxml.jackson.databind.JsonNode;
+import org.gcube.com.fasterxml.jackson.databind.node.ArrayNode;
+import org.gcube.com.fasterxml.jackson.databind.node.ObjectNode;
+import org.gcube.com.fasterxml.jackson.databind.node.TextNode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * @author Luca Frosini (ISTI - CNR)
  * 
@@ -32,46 +41,137 @@ public enum MatemathicsOperator {
 	BITWISE_XOR("_bitxor", " ^ ", ""),
 	ARRAY_CONCATENATION("_arrayconcat", " || ", "");
 	
-	protected final String operator;
-	protected final String matemathicsOperator;
+	protected static Logger logger = LoggerFactory.getLogger(MatemathicsOperator.class);
+	
+	public static final String VALUES_KEY = "values";
+	public static final String SEPARATOR_KEY = "separator";
+	public static final String AS_KEY = "as";
+	
+	protected final String operatorKey;
+	protected final String dbQueryOperator;
 	protected final String description;
 	
-	private MatemathicsOperator(String operator, String matemathicsOperator, String description) {
-		this.operator = operator;
-		this.matemathicsOperator = matemathicsOperator;
+	private MatemathicsOperator(String operatorKey, String dbQueryOperator, String description) {
+		this.operatorKey = operatorKey;
+		this.dbQueryOperator = dbQueryOperator;
 		this.description = description;
 	}
 	
-	public String getOperator() {
-		return operator;
+	public String getOperatorKey() {
+		return operatorKey;
 	}
 	
-	public String getMatemathicsOperator() {
-		return matemathicsOperator;
+	public String getDbQueryOperator() {
+		return dbQueryOperator;
 	}
 
 	public String getDescription() {
 		return description;
 	}
 
-	private static Set<String> operators;
 	private static Map<String,MatemathicsOperator> operatorByKey;
 	
 	static {
-		MatemathicsOperator.operators = new HashSet<>();
 		MatemathicsOperator.operatorByKey = new HashMap<>();
 		
-		for(MatemathicsOperator queryLogicalOperator : MatemathicsOperator.values()) {
-			MatemathicsOperator.operators.add(queryLogicalOperator.getOperator());
-			MatemathicsOperator.operatorByKey.put(queryLogicalOperator.getOperator(), queryLogicalOperator);
+		for(MatemathicsOperator matemathicsOperator : MatemathicsOperator.values()) {
+			MatemathicsOperator.operatorByKey.put(matemathicsOperator.getOperatorKey(), matemathicsOperator);
 		}
 	}
 	
 	public static Set<String> getOperators() {
-		return MatemathicsOperator.operators;
+		return new HashSet<>(MatemathicsOperator.operatorByKey.keySet());
 	}
 	
-	public static MatemathicsOperator getQueryLogicalOperator(String key) {
+	public static MatemathicsOperator getMatemathicsOperator(String key) {
 		return operatorByKey.get(key);
 	}
+
+	protected String getError(String key, Class<?> clazz, boolean mandatory) {
+		StringBuffer error = new StringBuffer();
+		error.append("Root emitting MatemathicsOperator (i.e. ");
+		error.append(this.operatorKey);
+		error.append(")");
+		error.append(" contains ");
+		if(mandatory) {
+			error.append("mandatory ");
+		}
+		error.append(key);
+		error.append(" which must be a");
+		error.append(clazz.getSimpleName());
+		error.append(". This is a client error. Please fix your query");
+		logger.error(error.toString());
+		throw new BadRequestException(error.toString());
+	}
+	
+	public String generateFieldToEmit(JsonNode jsonNode, String fieldPrefix) {
+		JsonNode jn = jsonNode.get(VALUES_KEY);
+		if(jn.isNull() || !jn.isArray()) {
+			getError(VALUES_KEY, ArrayNode.class, true);
+		}
+		String fieldSeparator = null;
+		if(this == MatemathicsOperator.SUM && jsonNode.has(SEPARATOR_KEY)) {
+			JsonNode sep = jsonNode.get(SEPARATOR_KEY);
+			if(!sep.isTextual()) {
+				getError(SEPARATOR_KEY, TextNode.class, false);
+			}
+			fieldSeparator = sep.asText();
+		}
+		StringBuffer sb = new StringBuffer();
+		sb.append("(");
+		sb.append(generateFieldToEmit((ArrayNode) jn, fieldSeparator, fieldPrefix));
+		JsonNode jnAs = jsonNode.get(AS_KEY);
+		if(jnAs.isNull() || !jnAs.isTextual()) {
+			getError(AS_KEY, TextNode.class, true);
+		}
+		sb.append(") AS `");
+		sb.append(jnAs.asText());
+		sb.append("`");
+		return sb.toString();
+	}
+	
+	protected StringBuffer addFieldPrefix(StringBuffer sb, String fieldPrefix) {
+		if(fieldPrefix !=null && fieldPrefix.trim().length()>0) {
+			sb.append(fieldPrefix.trim());
+			sb.append(".");
+		}
+		return sb;
+	}
+	
+	protected StringBuffer generateFieldToEmit(ArrayNode arrayNode, String fieldsSeparator, String fieldPrefix) {
+		StringBuffer buffer = new StringBuffer();
+		int size = arrayNode.size();
+		for(int i=0; i<size; i++) {
+			JsonNode jn = arrayNode.get(i);
+			if(jn.isObject()) {
+				ObjectNode on = (ObjectNode) jn;
+				String key = on.fieldNames().next();
+				MatemathicsOperator mo = MatemathicsOperator.getMatemathicsOperator(key);
+				ArrayNode an = (ArrayNode) on.get(key);
+				buffer.append("(");
+				buffer.append(mo.generateFieldToEmit(an, null, fieldPrefix));
+				buffer.append(")");
+			}
+			
+			if(jn.isTextual()) {
+				buffer = addFieldPrefix(buffer, fieldPrefix);
+				buffer.append(jn.asText());
+			}
+			
+			if(i<(size-1)) {
+				buffer.append(" ");
+				buffer.append(dbQueryOperator);
+				buffer.append(" ");
+				if(fieldsSeparator!=null) {
+					buffer.append("'");
+					buffer.append(fieldsSeparator);
+					buffer.append("' ");
+					buffer.append(dbQueryOperator);
+					buffer.append(" ");
+				}
+			}
+		}
+		return buffer;
+	}
+	
 }
diff --git a/src/test/java/org/gcube/informationsystem/resourceregistry/queries/JsonQueryTest.java b/src/test/java/org/gcube/informationsystem/resourceregistry/queries/JsonQueryTest.java
index e0f6401..7b66978 100644
--- a/src/test/java/org/gcube/informationsystem/resourceregistry/queries/JsonQueryTest.java
+++ b/src/test/java/org/gcube/informationsystem/resourceregistry/queries/JsonQueryTest.java
@@ -199,7 +199,7 @@ public class JsonQueryTest extends ContextTest {
 	@Test
 	public void testCreateMatchQuery() throws Exception {
 		File queriesDirectory = getProjectionQueriesDirectory();
-		File jsonQueryFile = new File(queriesDirectory, "EService-query.json");
+		File jsonQueryFile = new File(queriesDirectory, "HostingNode-query.json");
 		ObjectMapper objectMapper = new ObjectMapper();
 		JsonNode jsonNode = objectMapper.readTree(jsonQueryFile);
 		logger.info("Going to test the following JSON query {}", jsonNode.toString());
diff --git a/src/test/java/org/gcube/informationsystem/resourceregistry/queries/operators/MathematicsOperatorTest.java b/src/test/java/org/gcube/informationsystem/resourceregistry/queries/operators/MathematicsOperatorTest.java
new file mode 100644
index 0000000..c86ad6e
--- /dev/null
+++ b/src/test/java/org/gcube/informationsystem/resourceregistry/queries/operators/MathematicsOperatorTest.java
@@ -0,0 +1,38 @@
+package org.gcube.informationsystem.resourceregistry.queries.operators;
+
+import org.gcube.com.fasterxml.jackson.databind.JsonNode;
+import org.gcube.com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MathematicsOperatorTest {
+
+	protected static Logger logger = LoggerFactory.getLogger(MathematicsOperatorTest.class);
+	
+	public static final String JSON = "{ \n"
+			+ " \"values\" : [\n"
+			+ "		{\n"
+			+ "			\"_minus\" : [\n"
+			+ "				\"size\", \n"
+			+ "				\"used\" \n"
+			+ "			]\n"
+			+ "		},\n"
+			+ "		\"unit\" \n"
+			+ "	],\n"
+			+ "	\"separator\" : \" \",\n"
+			+ "	\"as\" : \"HD Space Left\"\n"
+			+ "}";
+	
+	@Test
+	public void testGenerateFieldToEmit() throws Exception {
+		ObjectMapper om = new ObjectMapper();
+		JsonNode jn = om.readTree(JSON);
+		String s = MatemathicsOperator.SUM.generateFieldToEmit(jn, "haspersistentmemory20");
+		logger.debug(s);
+	}
+	
+}
+
+
+
diff --git a/src/test/resources/projection-queries/EService.match.oquery b/src/test/resources/projection-queries/EService.match.oquery
index 9cf01b1..3cd8d05 100644
--- a/src/test/resources/projection-queries/EService.match.oquery
+++ b/src/test/resources/projection-queries/EService.match.oquery
@@ -21,9 +21,9 @@ MATCH
 	.outV('EService') { where: ($matched.eservice00 == $currentMatch)}
 
 RETURN
-	networkingfacet40.hostName AS Host,
-	softwarefacet20.group AS Group,
-	softwarefacet20.name AS Name,
-	softwarefacet20.version AS Version,
-	statefacet20.value AS Status,
-	eservice00.id AS ID
\ No newline at end of file
+	networkingfacet40.hostName AS `Host`,
+	softwarefacet20.group AS `Group`,
+	softwarefacet20.name AS `Name`,
+	softwarefacet20.version AS `Version`,
+	statefacet20.value AS `Status`,
+	eservice00.id AS `ID`
\ No newline at end of file
diff --git a/src/test/resources/projection-queries/EService.traversal.oquery b/src/test/resources/projection-queries/EService.traversal.oquery
deleted file mode 100644
index aaf6f84..0000000
--- a/src/test/resources/projection-queries/EService.traversal.oquery
+++ /dev/null
@@ -1,37 +0,0 @@
-SELECT id AS ID, 
-		outE("IsIdentifiedBy").inV("SoftwareFacet").name[0] AS `Name`, 
-        outE("IsIdentifiedBy").inV("SoftwareFacet").group[0] AS `Group`, 
-        outE("IsIdentifiedBy").inV("SoftwareFacet").version[0] AS `Version`,
-        outE("ConsistsOf").inV("StateFacet").value AS `Status`, 
-        inE("Activates").outV("HostingNode").outE("IsIdentifiedBy").inV("NetworkingFacet").hostName[0] AS `Host` 
-	FROM (
-	TRAVERSE outV("EService") FROM ( 
-		TRAVERSE inE("ConsistsOf") FROM ( 
-			SELECT FROM ( 
-				TRAVERSE inV("StateFacet") FROM ( 
-					TRAVERSE outE("ConsistsOf") FROM ( 
-						TRAVERSE outV("EService") FROM ( 
-							TRAVERSE inE("IsIdentifiedBy") FROM ( 
-								SELECT FROM ( 
-									TRAVERSE inV("SoftwareFacet") FROM ( 
-										TRAVERSE outE("IsIdentifiedBy") FROM ( 
-											TRAVERSE inV("EService") FROM ( 
-												TRAVERSE outE("Activates") FROM ( 
-													TRAVERSE outV("HostingNode") FROM ( 
-														TRAVERSE inE("IsIdentifiedBy") FROM ( 
-															SELECT FROM NetworkingFacet
-														)
-													)
-												)
-											)
-										)
-									)
-								)
-							)
-						)
-					)
-				)
-			)
-		)
-	)
-) WHERE @class INSTANCEOF "EService"
\ No newline at end of file
diff --git a/src/test/resources/projection-queries/HostingNode-query.json b/src/test/resources/projection-queries/HostingNode-query.json
index 6c85a7e..5164adc 100644
--- a/src/test/resources/projection-queries/HostingNode-query.json
+++ b/src/test/resources/projection-queries/HostingNode-query.json
@@ -1,66 +1,65 @@
 {
-	"_projection" : {
-		"type": "HostingNode",
-		"_emit" : { 
-			"id" : "Id",
-		},
-		"metadata" : {
-			"_emit" : {
-				"lastUpdateTime" : "Last Update Time"
-			}
-		},
-		"consistsOf": [
-			{
-				"type": "IsIdentifiedBy",
-				"target": {
-					"type": "NetworkingFacet",
-					"_emit" : {
-						"hostName" : "HostName"
-					}
-				}
-			},
-			{
-				"type": "ConsistsOf",
-				"target": {
-					"type": "StateFacet",
-					"_emit" : {
-						"value" : "Status"
-					}	
-				}
-			},
-			{
-				"type": "HasPersistentMemory",
-				"target": {
-					"type": "MemoryFacet",
-					"_concat" : { 
-						"values" : [
-							{
-								"_sub" : [ 
-									"size", 
-									"used" 
-								]
-							},
-							"unit" 
-						],
-						"separator" : " ",
-						"as" : "HD Space Left"
-					}
-				}
-			},
-			{
-				"type": "HasVolatileMemory",
-				"target": {
-					"type": "MemoryFacet",
-					"_concat" : {
-						"values" : [
-							"size",
-							"unit" 
-						],
-						"separator" : " ",
-						"as" : "Mem. Available."
-					}
+	"type": "HostingNode",
+	"_emit" : { 
+		"id" : "ID"
+	},
+	"metadata" : {
+		"_emit" : {
+			"lastUpdateTime" : "Last Update Time"
+		}
+	},
+	"consistsOf": [
+		{
+			"type": "IsIdentifiedBy",
+			"target": {
+				"type": "NetworkingFacet",
+				"_emit" : {
+					"hostName" : "HostName"
 				}
 			}
-		]
-	}
+		},
+		{
+			"type": "ConsistsOf",
+			"target": {
+				"type": "StateFacet",
+				"_emit" : {
+					"value" : "Status"
+				}	
+			}
+		},
+		{
+			"type": "HasPersistentMemory",
+			"target": {
+				"type": "MemoryFacet",
+				"_sum" : { 
+					"values" : [
+						{
+							"_minus" : [
+								"size", 
+								"used" 
+							]
+						},
+						"unit" 
+					],
+					"separator" : " ",
+					"as" : "HD Space Left"
+				}
+			}
+		},
+		{
+			"type": "HasVolatileMemory",
+			"target": {
+				"type": "MemoryFacet",
+				"jvmMaxMemory" : null,
+				"_sum" : {
+					"values" : [
+						"size",
+						"unit" 
+					],
+					"separator" : " ",
+					"as" : "Mem. Available."
+				}
+			}
+		}
+	]
 }
\ No newline at end of file
diff --git a/src/test/resources/projection-queries/HostingNode.match.oquery b/src/test/resources/projection-queries/HostingNode.match.oquery
new file mode 100644
index 0000000..6ba206d
--- /dev/null
+++ b/src/test/resources/projection-queries/HostingNode.match.oquery
@@ -0,0 +1,30 @@
+MATCH
+	{class: HostingNode, as: hostingnode0, where: ($currentMatch['@class'] INSTANCEOF 'HostingNode')}
+
+	.outE('IsIdentifiedBy') { as: isidentifiedby00, where: ($currentMatch['@class'] INSTANCEOF 'IsIdentifiedBy')}
+	.inV('NetworkingFacet') { as: networkingfacet000, where: ($currentMatch['@class'] INSTANCEOF 'NetworkingFacet')}
+	.inE('IsIdentifiedBy')  { where: ($matched.isidentifiedby00 == $currentMatch)}
+	.outV('HostingNode') { where: ($matched.hostingnode0 == $currentMatch)}
+
+	.outE('ConsistsOf') { as: consistsof01, where: ($currentMatch['@class'] INSTANCEOF 'ConsistsOf')}
+	.inV('StateFacet') { as: statefacet010, where: ($currentMatch['@class'] INSTANCEOF 'StateFacet')}
+	.inE('ConsistsOf')  { where: ($matched.consistsof01 == $currentMatch)}
+	.outV('HostingNode') { where: ($matched.hostingnode0 == $currentMatch)}
+
+	.outE('HasPersistentMemory') { as: haspersistentmemory02, where: ($currentMatch['@class'] INSTANCEOF 'HasPersistentMemory')}
+	.inV('MemoryFacet') { as: memoryfacet020, where: ($currentMatch['@class'] INSTANCEOF 'MemoryFacet')}
+	.inE('HasPersistentMemory')  { where: ($matched.haspersistentmemory02 == $currentMatch)}
+	.outV('HostingNode') { where: ($matched.hostingnode0 == $currentMatch)}
+
+	.outE('HasVolatileMemory') { as: hasvolatilememory03, where: ($currentMatch['@class'] INSTANCEOF 'HasVolatileMemory')}
+	.inV('MemoryFacet') { as: memoryfacet030, where: (($currentMatch['@class'] INSTANCEOF 'MemoryFacet') AND (jvmMaxMemory IS null))}
+	.inE('HasVolatileMemory')  { where: ($matched.hasvolatilememory03 == $currentMatch)}
+	.outV('HostingNode') { where: ($matched.hostingnode0 == $currentMatch)}
+
+RETURN
+	networkingfacet000.hostName AS `HostName`,
+	statefacet010.value AS `Status`,
+	((memoryfacet020.size  -  memoryfacet020.used)  +  ' '  +  memoryfacet020.unit) AS `HD Space Left`,
+	(memoryfacet030.size  +  ' '  +  memoryfacet030.unit) AS `Mem. Available.`,
+	hostingnode0.id AS `ID`,
+	hostingnode0.lastUpdateTime AS `Last Update Time`
\ No newline at end of file