diff --git a/src/main/java/de/ids_mannheim/korap/query/serialize/AbstractSyntaxTree.java b/src/main/java/de/ids_mannheim/korap/query/serialize/AbstractSyntaxTree.java
index 2de2d18..31a2ca5 100644
--- a/src/main/java/de/ids_mannheim/korap/query/serialize/AbstractSyntaxTree.java
+++ b/src/main/java/de/ids_mannheim/korap/query/serialize/AbstractSyntaxTree.java
@@ -104,7 +104,7 @@
 	protected LinkedHashMap<String, Object> makeDocGroup(String relation) {
 		LinkedHashMap<String, Object> term = new LinkedHashMap<String, Object>();
 		term.put("@type", "korap:docGroup");
-		term.put("relation", "relation:"+relation);
+		term.put("operation", "operation:"+relation);
 		term.put("operands", new ArrayList<Object>());
 		return term;
 	}
diff --git a/src/main/java/de/ids_mannheim/korap/query/serialize/CollectionQueryTree.java b/src/main/java/de/ids_mannheim/korap/query/serialize/CollectionQueryTree.java
index 4c663e2..a33bc2e 100644
--- a/src/main/java/de/ids_mannheim/korap/query/serialize/CollectionQueryTree.java
+++ b/src/main/java/de/ids_mannheim/korap/query/serialize/CollectionQueryTree.java
@@ -71,7 +71,7 @@
 
         if (nodeCat.equals("relation")) {
         	String operator = node.getChild(1).getChild(0).toStringTree(parser).equals("&") ? "and" : "or"; 
-            LinkedHashMap<String, Object> relationGroup = makeGroup(operator);
+            LinkedHashMap<String, Object> relationGroup = makeDocGroup(operator);
             putIntoSuperObject(relationGroup);
             objectStack.push(relationGroup);
             stackedObjects++;
@@ -98,7 +98,7 @@
                 term.put("match", "match:" + interpretMatch(match));
                 putIntoSuperObject(term);
             } else { // (valueNodes.size()==2)
-                LinkedHashMap<String, Object> termGroup = makeGroup("and");
+                LinkedHashMap<String, Object> termGroup = makeDocGroup("and");
                 ArrayList<Object> termGroupOperands = (ArrayList<Object>) termGroup.get("operands");
 
                 LinkedHashMap<String, Object> term1 = makeDoc();
diff --git a/src/test/java/CollectionQueryTreeTest.java b/src/test/java/CollectionQueryTreeTest.java
index 0a6b333..4fe87b1 100644
--- a/src/test/java/CollectionQueryTreeTest.java
+++ b/src/test/java/CollectionQueryTreeTest.java
@@ -41,7 +41,7 @@
 	public void testTwoConjuncts() throws QueryException {
 		query = "textClass=Sport & year=2014";
 		expected = 
-				"{@type=korap:group, operation=operation:and, operands=[" +
+				"{@type=korap:docGroup, operation=operation:and, operands=[" +
 					"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}," +
 					"{@type=korap:doc, key=year, value=2014, match=match:eq}" +
 				"]}";
@@ -55,9 +55,9 @@
 	public void testThreeConjuncts() throws QueryException {
 		query = "textClass=Sport & year=2014 & corpusID=WPD";
 		expected = 
-				"{@type=korap:group, operation=operation:and, operands=[" +
+				"{@type=korap:docGroup, operation=operation:and, operands=[" +
 					"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}," +
-					"{@type=korap:group, operation=operation:and, operands=[" +
+					"{@type=korap:docGroup, operation=operation:and, operands=[" +
 						"{@type=korap:doc, key=year, value=2014, match=match:eq}," +
 						"{@type=korap:doc, key=corpusID, value=WPD, match=match:eq}" +
 					"]}" +
@@ -73,7 +73,7 @@
 	public void testTwoDisjuncts() throws QueryException {
 		query = "textClass=Sport | year=2014";
 		expected = 
-				"{@type=korap:group, operation=operation:or, operands=[" +
+				"{@type=korap:docGroup, operation=operation:or, operands=[" +
 					"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}," +
 					"{@type=korap:doc, key=year, value=2014, match=match:eq}" +
 				"]}";
@@ -87,9 +87,9 @@
 	public void testThreeDisjuncts() throws QueryException {
 		query = "textClass=Sport | year=2014 | corpusID=WPD";
 		expected = 
-				"{@type=korap:group, operation=operation:or, operands=[" +
+				"{@type=korap:docGroup, operation=operation:or, operands=[" +
 					"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}," +
-					"{@type=korap:group, operation=operation:or, operands=[" +
+					"{@type=korap:docGroup, operation=operation:or, operands=[" +
 						"{@type=korap:doc, key=year, value=2014, match=match:eq}," +
 						"{@type=korap:doc, key=corpusID, value=WPD, match=match:eq}" +
 					"]}" +
@@ -106,8 +106,8 @@
 		query = "(textClass=Sport | textClass=ausland) & corpusID=WPD";
 		expected = 
 			
-				"{@type=korap:group, operation=operation:and, operands=[" +
-					"{@type=korap:group, operation=operation:or, operands=[" +
+				"{@type=korap:docGroup, operation=operation:and, operands=[" +
+					"{@type=korap:docGroup, operation=operation:or, operands=[" +
 						"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}," +
 						"{@type=korap:doc, key=textClass, value=ausland, match=match:eq}" +
 					"]}," +
@@ -121,8 +121,8 @@
 		query = "(textClass=Sport & textClass=ausland) & corpusID=WPD";
 		expected = 
 			
-				"{@type=korap:group, operation=operation:and, operands=[" +
-					"{@type=korap:group, operation=operation:and, operands=[" +
+				"{@type=korap:docGroup, operation=operation:and, operands=[" +
+					"{@type=korap:docGroup, operation=operation:and, operands=[" +
 						"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}," +
 						"{@type=korap:doc, key=textClass, value=ausland, match=match:eq}" +
 					"]}," +
@@ -136,12 +136,12 @@
 		query = "(textClass=Sport & textClass=ausland) | (corpusID=WPD & author=White)";
 		expected = 
 			
-				"{@type=korap:group, operation=operation:or, operands=[" +
-					"{@type=korap:group, operation=operation:and, operands=[" +
+				"{@type=korap:docGroup, operation=operation:or, operands=[" +
+					"{@type=korap:docGroup, operation=operation:and, operands=[" +
 						"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}," +
 						"{@type=korap:doc, key=textClass, value=ausland, match=match:eq}" +
 					"]}," +
-					"{@type=korap:group, operation=operation:and, operands=[" +
+					"{@type=korap:docGroup, operation=operation:and, operands=[" +
 						"{@type=korap:doc, key=corpusID, value=WPD, match=match:eq}," +
 						"{@type=korap:doc, key=author, value=White, match=match:eq}" +
 					"]}" +
@@ -153,14 +153,14 @@
 		
 		query = "(textClass=Sport & textClass=ausland) | (corpusID=WPD & author=White & year=2010)";
 		expected = 
-				"{@type=korap:group, operation=operation:or, operands=[" +
-					"{@type=korap:group, operation=operation:and, operands=[" +
+				"{@type=korap:docGroup, operation=operation:or, operands=[" +
+					"{@type=korap:docGroup, operation=operation:and, operands=[" +
 						"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}," +
 						"{@type=korap:doc, key=textClass, value=ausland, match=match:eq}" +
 					"]}," +
-					"{@type=korap:group, operation=operation:and, operands=[" +
+					"{@type=korap:docGroup, operation=operation:and, operands=[" +
 						"{@type=korap:doc, key=corpusID, value=WPD, match=match:eq}," +
-						"{@type=korap:group, operation=operation:and, operands=[" +
+						"{@type=korap:docGroup, operation=operation:and, operands=[" +
 							"{@type=korap:doc, key=author, value=White, match=match:eq}," +
 							"{@type=korap:doc, key=year, value=2010, match=match:eq}" +
 						"]}" +
@@ -177,7 +177,7 @@
 		// search for pubDate between 1990 and 2010!
 		query = "1990<pubDate<2010";
 		expected = 
-				"{@type=korap:group, operation=operation:and, operands=[" +
+				"{@type=korap:docGroup, operation=operation:and, operands=[" +
 					"{@type=korap:doc, key=pubDate, value=1990, match=match:gt}," +
 					"{@type=korap:doc, key=pubDate, value=2010, match=match:lt}" +
 				"]}";
@@ -250,7 +250,7 @@
 		
 		query = "[base=Schwalbe] & [orth=Foul]";
 		expected = 
-				"{@type=korap:group, operation=operation:and, operands=[" +
+				"{@type=korap:docGroup, operation=operation:and, operands=[" +
 						"{@type=korap:token, wrap={@type=korap:term, layer=lemma, key=Schwalbe, match=match:eq}}," +
 						"{@type=korap:token, wrap={@type=korap:term, layer=orth, key=Foul, match=match:eq}}" +
 					"]}";
@@ -264,7 +264,7 @@
 	public void testContentMetaMixed() throws QueryException {
 		query = "textClass=Sport & [base=Schwalbe]";
 		expected = 
-				"{@type=korap:group, operation=operation:and, operands=[" +
+				"{@type=korap:docGroup, operation=operation:and, operands=[" +
 					"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}," +
 					"{@type=korap:token, wrap={@type=korap:term, layer=lemma, key=Schwalbe, match=match:eq}}" +
 				"]}";
@@ -275,7 +275,7 @@
 		
 		query = "[base=Schwalbe] & textClass=Sport";
 		expected = 
-				"{@type=korap:group, operation=operation:and, operands=[" +
+				"{@type=korap:docGroup, operation=operation:and, operands=[" +
 					"{@type=korap:token, wrap={@type=korap:term, layer=lemma, key=Schwalbe, match=match:eq}}," +
 					"{@type=korap:doc, key=textClass, value=Sport, match=match:eq}" +
 				"]}";