diff --git a/procedures/query/applyPOV.sql b/procedures/query/applyPOV.sql
index 732854be91b5dcda817da3faa00c9ba727a31e3e..0d0ee41785968e90f5d76a6f9ecb1be24170f489 100644
--- a/procedures/query/applyPOV.sql
+++ b/procedures/query/applyPOV.sql
@@ -82,6 +82,7 @@ POV_LABEL: BEGIN
     DECLARE distinctUnits INT DEFAULT 0;
     DECLARE usedStdUnit BIGINT DEFAULT NULL;
     DECLARE keepTabl VARCHAR(255) DEFAULT NULL;
+    DECLARE existence_op VARCHAR(255) DEFAULT "EXISTS";
 
     IF o = '->' THEN
         #-- special case: pure reference property
@@ -210,7 +211,10 @@ POV_LABEL: BEGIN
             ));
             SET sNameData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `name_data` UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_name_data` ', CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `name_data` AS subdata WHERE subdata.value ', o, ' ? UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_name_data` AS subdata WHERE subdata.value ', o, '?'));
             SET sEnumData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `enum_data` UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_enum_data` ', CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `enum_data` AS subdata WHERE subdata.value ', o, ' ? UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_enum_data` AS subdata WHERE subdata.value ', o, '?'));
-            SET sRefData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `reference_data` UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_reference_data`', IF(refIdsTable IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `reference_data` AS subdata WHERE EXISTS (SELECT 1 FROM `', refIdsTable, '` AS refIdsTable WHERE subdata.value=refIdsTable.id LIMIT 1) UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_reference_data` AS subdata WHERE EXISTS (SELECT 1 FROM `', refIdsTable, '` AS refIdsTable WHERE subdata.value=refIdsTable.id LIMIT 1)')));
+            IF o = "!=" AND refIdsTable IS NOT NULL THEN
+                SET existence_op = "NOT EXISTS";
+            END IF;
+            SET sRefData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `reference_data` UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_reference_data`', IF(refIdsTable IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `reference_data` AS subdata WHERE ', existence_op, ' (SELECT 1 FROM `', refIdsTable, '` AS refIdsTable WHERE subdata.value=refIdsTable.id LIMIT 1) UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_reference_data` AS subdata WHERE ', existence_op, ' (SELECT 1 FROM `', refIdsTable, '` AS refIdsTable WHERE subdata.value=refIdsTable.id LIMIT 1)')));
             SET sDoubleData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT subdata.domain_id, subdata.entity_id, _get_head_iversion(subdata.entity_id) AS _iversion, subdata.property_id FROM `double_data` AS subdata UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_double_data` ', IF(vDouble IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id), property_id FROM `double_data` AS subdata WHERE ', getDoubleWhereClause(vDouble,unit_sig,vDoubleStdUnit,stdUnit_sig,o), ' UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_double_data` AS subdata WHERE ', getDoubleWhereClause(vDouble, unit_sig, vDoubleStdUnit, stdUnit_sig, o))));
             SET sIntData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT subdata.domain_id, subdata.entity_id, _get_head_iversion(subdata.entity_id) AS _iversion, subdata.property_id FROM `integer_data` AS subdata UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_integer_data`', IF(vInt IS NULL AND vDoubleStdUnit IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `integer_data` AS subdata WHERE ', getDoubleWhereClause(vInt, unit_sig, vDoubleStdUnit, stdUnit_sig, o), ' UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_integer_data` AS subdata WHERE ', getDoubleWhereClause(vInt, unit_sig, vDoubleStdUnit, stdUnit_sig, o))));
             SET sDatetimeData = IF(vText IS NULL,' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `datetime_data` UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_datetime_data`', IF(vDateTime IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, _get_head_iversion(entity_id) AS _iversion, property_id FROM `datetime_data` AS subdata WHERE ',getDateTimeWhereClause(vDateTime,o), ' UNION ALL SELECT DISTINCT domain_id, entity_id, _iversion, property_id FROM `archive_datetime_data` AS subdata WHERE ',getDateTimeWhereClause(vDateTime,o))));
@@ -220,7 +224,10 @@ POV_LABEL: BEGIN
             SET sTextData = IF(vText IS NULL, 'SELECT DISTINCT domain_id, entity_id, property_id FROM `text_data`', CONCAT('SELECT DISTINCT domain_id, entity_id, property_id FROM `text_data` AS subdata WHERE subdata.value ',o,' ?'));
             SET sNameData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `name_data`', CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `name_data` AS subdata WHERE subdata.value ', o, ' ?'));
             SET sEnumData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `enum_data`', CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `enum_data` AS subdata WHERE subdata.value ', o, ' ?'));
-            SET sRefData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `reference_data`', IF(refIdsTable IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `reference_data` AS subdata WHERE EXISTS (SELECT 1 FROM `', refIdsTable, '` AS refIdsTable WHERE subdata.value=refIdsTable.id LIMIT 1)')));
+            IF o = "!=" AND refIdsTable IS NOT NULL THEN
+                SET existence_op = "NOT EXISTS";
+            END IF;
+            SET sRefData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `reference_data`', IF(refIdsTable IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `reference_data` AS subdata WHERE ',existence_op ,' (SELECT 1 FROM `', refIdsTable, '` AS refIdsTable WHERE subdata.value=refIdsTable.id LIMIT 1)')));
             SET sDoubleData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT subdata.domain_id, subdata.entity_id, subdata.property_id FROM `double_data` AS subdata', IF(vDouble IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `double_data` AS subdata WHERE ', getDoubleWhereClause(vDouble,unit_sig,vDoubleStdUnit,stdUnit_sig,o))));
             SET sIntData = IF(vText IS NULL, ' UNION ALL SELECT DISTINCT subdata.domain_id, subdata.entity_id, subdata.property_id FROM `integer_data` AS subdata', IF(vInt IS NULL AND vDoubleStdUnit IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `integer_data` AS subdata WHERE ', getDoubleWhereClause(vInt, unit_sig, vDoubleStdUnit, stdUnit_sig, o))));
             SET sDatetimeData = IF(vText IS NULL,' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `datetime_data`', IF(vDateTime IS NULL, NULL, CONCAT(' UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `datetime_data` AS subdata WHERE ',getDateTimeWhereClause(vDateTime,o))));