Add optional merging part to solution

model_examples/model_extension/saxony.transportation_network

 <?xml version="1.0" encoding="UTF-8"?>
 <transportation_network:TransportationNetwork xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:transportation_network="http://www.stgroup.org/transportation_network" identifier="saxony">
   <roadnetworks identifier="DG/1" length="95.0" source="//@locations.0" target="//@locations.3">
-    <roads identifier="A4" length="95.0"/>
+    <roads identifier="A4-E" length="95.0"/>
   </roadnetworks>
   <roadnetworks identifier="DL/3" length="20.0" source="//@locations.0" target="//@locations.4">
-    <roads identifier="A4" length="20.0"/>
+    <roads identifier="A4-W" length="20.0"/>
   </roadnetworks>
   <roadnetworks identifier="DL/2" length="67.0" source="//@locations.4" target="//@locations.5">
     <roads identifier="A14" length="67.0"/>
@@ -12,8 +12,8 @@
   <roadnetworks identifier="DL/1" length="15.0" source="//@locations.5" target="//@locations.2">
     <roads identifier="A38" length="15.0"/>
   </roadnetworks>
-  <roadnetworks identifier="DC/1" length="64.0" source="//@locations.0" target="//@locations.1">
-    <roads identifier="A4" length="64.0"/>
+  <roadnetworks identifier="DC/1" length="44.0" source="//@locations.4" target="//@locations.1">
+    <roads identifier="A4-W" length="44.0"/>
   </roadnetworks>
   <roadnetworks identifier="LC/1" length="69.0" source="//@locations.2" target="//@locations.1">
     <roads identifier="A72" length="69.0"/>

model_examples/model_extension/saxony_original.transportation_network

 <?xml version="1.0" encoding="UTF-8"?>
 <transportation_network:TransportationNetwork xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:transportation_network="http://www.stgroup.org/transportation_network" identifier="saxony">
   <roadnetworks identifier="DG" length="95.0" source="//@locations.0" target="//@locations.3">
-    <roads identifier="A4" length="95.0"/>
+    <roads identifier="A4-E" length="95.0"/>
   </roadnetworks>
   <roadnetworks identifier="DL" length="102.0" source="//@locations.0" target="//@locations.2">
-    <roads identifier="A4" length="20.0"/>
+    <roads identifier="A4-W" length="20.0"/>
     <roads identifier="A14" length="67.0"/>
     <roads identifier="A38" length="15.0"/>
   </roadnetworks>
   <roadnetworks identifier="DC" length="64.0" source="//@locations.0" target="//@locations.1">
-    <roads identifier="A4" length="64.0"/>
+    <roads identifier="A4-W" length="64.0"/>
   </roadnetworks>
   <roadnetworks identifier="LC" length="69.0" source="//@locations.2" target="//@locations.1">
     <roads identifier="A72" length="69.0"/>

stgroup.mdsd.transportation_network.transformation/model_extension/model_extension.etl

@@ -51,12 +51,49 @@ rule SplitRoadNetworks
 	
 }
 
+
 rule deleteEmptyRoadNetworks 
 	transform s : source!RoadNetwork
 	to t  : target!EObject
 	{
 	
-	guard: not s.roads.isEmpty()
-	
+	if(s.roads.isEmpty()){
 		delete s;
 	}
+}
+
+
+/*
+* Optional Part for merging Road Networks with the help of an operation
+*/
+
+rule mergeRoadNetworks 
+	transform s : source!TransportationNetwork
+	to t : target!EObject{
+	
+	for (r in s.roadNetworks) { 
+		var toBeMergeRNs = r.RNtoMerge();
+		if(not toBeMergeRNs.isEmpty()){
+			toBeMergeRNs.add(r);
+			var minRoad = toBeMergeRNs.sortBy(rn | rn.roads.first().length).first();
+			toBeMergeRNs.remove(minRoad);
+			for (mergingRN in toBeMergeRNs) { 
+				mergingRN.source = minRoad.target;
+				mergingRN.roads.first().length -= minRoad.roads.first().length;
+				mergingRN.length = mergingRN.roads.first().length;
+			}
+		}
+	}
+}
+
+operation source!RoadNetwork RNtoMerge() : Set {
+	if(self.eContainer() <> null){
+		return self.eContainer().roadNetworks.select(rn | rn.source.equals(self.source) 
+														   and not (rn == self))
+											 .select(rn | (rn.roads.size() == 1) 
+											 			   and (rn.roads.first().identifier == self.roads.first().identifier));
+	} else{
+		return new Set;
+	}
+	
+}