diff --git a/src/main/java/haflow/engine/model/DirectedGraph.java b/src/main/java/haflow/engine/model/DirectedGraph.java
index ca1bbcc..2e2319e 100644
--- a/src/main/java/haflow/engine/model/DirectedGraph.java
+++ b/src/main/java/haflow/engine/model/DirectedGraph.java
@@ -98,22 +98,22 @@ public class DirectedGraph {
 //		return ret;
 //	}
 	
-//	private List<Node> getNodeList() {
-//		return nodeList;
-//	}
-//
-//	private void setNodeList(List<Node> nodeList) {
-//		this.nodeList = nodeList;
-//	}
-//
-//	private List<Edge> getEdgeList() {
-//		return edgeList;
-//	}
-//
-//	private void setEdgeList(List<Edge> edgeList) {
-//		this.edgeList = edgeList;
-//	}
-//
+	public List<Node> getNodeList() {
+		return nodeList;
+	}
+
+	public void setNodeList(List<Node> nodeList) {
+		this.nodeList = nodeList;
+	}
+
+	public List<Edge> getEdgeList() {
+		return edgeList;
+	}
+
+	public void setEdgeList(List<Edge> edgeList) {
+		this.edgeList = edgeList;
+	}
+
 //	private Node getStartNode() {
 //		return startNode;
 //	}
diff --git a/src/main/java/haflow/engine/oozie/OozieEngine.java b/src/main/java/haflow/engine/oozie/OozieEngine.java
index 23f5bde..fb12750 100644
--- a/src/main/java/haflow/engine/oozie/OozieEngine.java
+++ b/src/main/java/haflow/engine/oozie/OozieEngine.java
@@ -15,6 +15,8 @@ import haflow.engine.model.TopologicalSort;
 import haflow.module.AbstractHiveModule;
 import haflow.module.AbstractJavaModule;
 import haflow.module.Module;
+import haflow.module.ModuleConfiguration;
+import haflow.module.ModuleEndpoint;
 import haflow.module.basic.EndModule;
 import haflow.module.basic.StartModule;
 import haflow.module.util.ModuleUtil;
@@ -141,79 +143,132 @@ public class OozieEngine extends AbstractEngine {
 					.searchForModuleClasses();
 
 			Set<Node> nodes = flow.getNodes();
-
-			messageBuilder.append("Start parsing flow ..." + "<br>");
+			
+			messageBuilder.append("Finding start node ...");
 			List<Node> startNodes = findStartNodes(nodes, moduleClasses);
-			if (startNodes.size() != 1) {
-				messageBuilder.append("Error: Wrong start node number "
-						+ startNodes.size());
-			} else {
+			if (startNodes.size() == 1) {
+				messageBuilder.append(" done"  + "<br>");
 				DirectedGraph graph = new DirectedGraph(flow.getNodes(),
 						flow.getEdges(), startNodes.get(0));
-				List<Integer> sorted = new TopologicalSort(graph).getOrder();
+				
+				messageBuilder.append("Start validating flow inputs and outputs ...");
+				boolean isValidGraph = validateGraph(graph, moduleClasses, messageBuilder);//TODO
+				if (isValidGraph) {
+					messageBuilder.append(" done"  + "<br>");
+					
+					messageBuilder.append("Start sorting nodes ...");
+					List<Integer> sorted = new TopologicalSort(graph)
+							.getOrder();
 
-				if (sorted == null) {
-					messageBuilder.append("Error: Flow has Circles!");
-				} else {
-					String flowName = flow.getName();
-					String workflowXml = genWorkflowXml(flowName, sorted,
-							moduleClasses, graph);
-
-					messageBuilder.append("Parsing flow ... Finised" + "<br>");
-					messageBuilder.append("Start deploying flow ..." + "<br>");
-
-					String localDeployPath = this.getClusterConfiguration()
-							.getProperty(ClusterConfiguration.WORKSPACE_LOCAL)
-							+ flowName;
-					boolean deloyedLocally = this.getFlowDeployService()
-							.deployFlowLocal(localDeployPath, workflowXml,
-									getJarPaths(nodes, moduleClasses));
-					if (deloyedLocally) {
-						messageBuilder.append(flowName
-								+ " has been deployed locally!" + "<br>");
-
-						String hdfsDeployPath = this.getClusterConfiguration()
-								.getProperty(
-										ClusterConfiguration.WORKSPACE_HDFS)
-								+ flowName;
-						boolean deleted = this.getHdfsService()
-								.deleteDirectory(hdfsDeployPath);
-						if (deleted) {
-							messageBuilder.append("Old folder deleted: "
-									+ hdfsDeployPath + "<br>");
-						}
-
-						boolean deployedToHdfs = this.getHdfsService()
-								.uploadFile(localDeployPath, hdfsDeployPath);
-						if (deployedToHdfs) {
-							messageBuilder.append(flowName
-									+ " has been uploaded to hdfs!" + "<br>");
-
-							String jobId = this.getOozieService().runJob(
-									flowName);
-							if (jobId == null) {
-								messageBuilder.append("Failed to commit job: "
-										+ flowName + "<br>");
-							} else {
-								messageBuilder.append("Job commited! Job id : "
-										+ jobId + "<br>");
-								model.setCommitted(true);
-								model.setJobId(jobId);
+					if (sorted != null) {
+						messageBuilder.append(" done"  + "<br>");
+						
+						messageBuilder.append("Start validating configurations of each node ..."
+								+ "<br>");
+						boolean isValide = validateEachNode(flow, moduleClasses, messageBuilder);// TODO
+						if (isValide) {
+							messageBuilder.append(" done"  + "<br>");
+							
+							messageBuilder.append("Start generating Oozie xml ...");
+							String flowName = flow.getName();
+							String workflowXml = null;
+							try {
+								workflowXml = genWorkflowXml(flowName, sorted,
+										moduleClasses, graph);
+							} catch (Exception e) {
+								messageBuilder.append(e.getMessage());
 							}
-						} else {
-							messageBuilder.append(flowName
-									+ " failed to be uploaded to hdfs!" + "<br>");
-						}
-					} else {
-						messageBuilder.append(flowName
-								+ " failed to be deployed locally!" + "<br>");
-					}
+
+							if (workflowXml != null){
+								messageBuilder.append(" done"  + "<br>");
+								
+								messageBuilder
+										.append("Start deploying flow locally ...");
+								String localDeployPath = this
+										.getClusterConfiguration()
+										.getProperty(
+												ClusterConfiguration.WORKSPACE_LOCAL)
+										+ flowName;
+								boolean deloyedLocally = this
+										.getFlowDeployService()
+										.deployFlowLocal(
+												localDeployPath,
+												workflowXml,
+												getJarPaths(nodes,
+														moduleClasses));
+								if (deloyedLocally) {
+									messageBuilder.append(" done"  + "<br>");
+									
+									String hdfsDeployPath = this
+											.getClusterConfiguration()
+											.getProperty(
+													ClusterConfiguration.WORKSPACE_HDFS)
+											+ flowName;
+									boolean deleted = this.getHdfsService()
+											.deleteDirectory(hdfsDeployPath);
+									if (deleted) {
+										messageBuilder
+												.append( "<br>" + "Old folder deleted: "
+														+ hdfsDeployPath
+														+ "<br>");
+									}
+
+									messageBuilder
+											.append("Start deploying flow to HDFS ...");
+									boolean deployedToHdfs = this
+											.getHdfsService().uploadFile(
+													localDeployPath,
+													hdfsDeployPath);
+									if (deployedToHdfs) {
+										messageBuilder.append(" done"  + "<br>");
+										
+										messageBuilder
+												.append("Start committing job to Oozie ...");
+
+										String jobId = this.getOozieService()
+												.runJob(flowName);
+										if (jobId != null) {
+											messageBuilder.append(" done"  + "<br>");
+											
+											messageBuilder
+													.append("Job commited! Job id : "
+															+ jobId + "<br>");
+											model.setCommitted(true);
+											model.setJobId(jobId);
+										} else {
+
+											messageBuilder
+													.append("Error :" + "Failed to commit job: "
+															+ flowName + "<br>");
+										}
+									} else {
+										messageBuilder
+												.append("Error :" + flowName
+														+ " failed to be uploaded to hdfs!"
+														+ "<br>");
+									}
+								}else {
+									messageBuilder.append("Error :" + flowName
+											+ " failed to be deployed locally!"
+											+ "<br>");
+								} 
+							}else  {
+								messageBuilder
+								.append("Error : Failed to generate Oozie xml!");
+							} 
+						}else {
+							messageBuilder.append("Error : Invalid flow!");
+						} 
+					}else {
+						messageBuilder.append("Error: Flow has Circles!");
+					} 
 				}
+			} else {
+				messageBuilder.append("Error: Wrong start node number "
+						+ startNodes.size());
 			}
 
-//			System.out.println(messageBuilder.toString());
 			model.setMessage(messageBuilder.toString());
-//			System.out.println(messageBuilder.toString());
 			logger.info(messageBuilder.toString());
 			return model;
 		} catch (Exception e) {
@@ -264,6 +319,87 @@ public class OozieEngine extends AbstractEngine {
 		}
 	}
 
+	private boolean validateGraph(DirectedGraph graph,
+			Map<UUID, Class<?>> moduleClasses, StringBuilder messageBuilder) {
+		List<Edge> edges = graph.getEdgeList();
+
+		for (int i = 0; i < graph.getNodeCount(); i++) {
+			Node node = graph.getNode(i);
+			UUID moduleId = node.getModuleId();
+			Class<?> moduleClass = moduleClasses.get(moduleId);
+			Module annotation = moduleClass.getAnnotation(Module.class);
+			ModuleEndpoint[] inputs = annotation.inputs();
+			ModuleEndpoint[] outputs = annotation.outputs();
+
+			for (ModuleEndpoint input : inputs) {
+				String inputName = input.name();
+				boolean found = false;
+				for (Edge edge : edges) {
+					if (edge.getTargetNode().getId().equals(node.getId())
+							&& inputName.equals(edge.getTargetEndpoint())){
+						found = true;
+						break;
+					}
+				}				
+				if( !found){
+					messageBuilder.append("Empty input of node " + node.getName() + " input " + inputName);
+					return false;
+				}
+			}
+			
+			for(ModuleEndpoint output : outputs){
+				String outputName = output.name();
+				boolean found = false;
+				for( Edge edge : edges) {
+					if( edge.getSourceNode().getId().equals(node.getId()) 
+							&& outputName.equals(edge.getSourceEndpoint())){
+						found = true;
+						break;
+					}
+				}
+				if ( !found){
+					messageBuilder.append("Empty output of node " + node.getName() + " output " + outputName + "<br>");
+					return false;
+				}
+			}
+		}
+		return true;// TODO
+	}
+	
+	/**
+	 * Check if each node of the flow has all the required configurations.
+	 * @param flow
+	 * @param moduleClasses
+	 * @param messageBuilder
+	 * @return
+	 */
+	private boolean validateEachNode(Flow flow, Map<UUID, Class<?>> 
+		moduleClasses, StringBuilder messageBuilder){
+		Set<Node> nodes = flow.getNodes();
+		for( Node node : nodes){
+			Class<?> moduleClass = moduleClasses.get(node.getModuleId());
+			Module anno = moduleClass.getAnnotation(Module.class);
+			ModuleConfiguration[] moduleConfs = anno.configurations();
+			List<NodeConfiguration> nodeConfs = this.getNodeConfigurationService().getNodeConfiguration(node.getId());
+			for(ModuleConfiguration moduleConf : moduleConfs){
+				if( moduleConf.required()){
+					boolean found = false;
+					for( NodeConfiguration nodeConf : nodeConfs){
+						if( nodeConf.getKey().equals(moduleConf.key()) && nodeConf.getValue() != null & nodeConf.getValue().trim() != ""){
+							found = true;
+							break;
+						}
+					}
+					if( !found){
+						messageBuilder.append("No value for " + moduleConf.key() + " of node " + node.getName() + "<br>");
+						return false;
+					}
+				}
+			}
+		}
+		return true;
+	}
+	
 	private String genWorkflowXml(String flowName, List<Integer> sorted,
 			Map<UUID, Class<?>> moduleClasses, DirectedGraph graph)
 			throws InstantiationException, IllegalAccessException {
@@ -293,8 +429,8 @@ public class OozieEngine extends AbstractEngine {
 					Edge path = v.getPath();
 					outputs.put(path.getSourceEndpoint(), // "ok"
 							path.getTargetNode());
-					System.out.println(path.getSourceEndpoint());
-					System.out.println(path.getTargetNode().getName());
+					System.out.println(path.getSourceEndpoint() 
+							+ " to " + path.getTargetNode().getName());
 				}
 			}
 
diff --git a/src/main/java/haflow/module/ModuleConfiguration.java b/src/main/java/haflow/module/ModuleConfiguration.java
index 31a7fd3..1c58351 100644
--- a/src/main/java/haflow/module/ModuleConfiguration.java
+++ b/src/main/java/haflow/module/ModuleConfiguration.java
@@ -15,4 +15,6 @@ public @interface ModuleConfiguration {
 	String pattern();
 	
 	ModuleConfigurationType type();
+	
+	boolean required() default false;
 }
diff --git a/src/main/java/haflow/ui/helper/RunHistoryHelper.java b/src/main/java/haflow/ui/helper/RunHistoryHelper.java
index 13bb079..e99a3c3 100644
--- a/src/main/java/haflow/ui/helper/RunHistoryHelper.java
+++ b/src/main/java/haflow/ui/helper/RunHistoryHelper.java
@@ -6,6 +6,8 @@ import haflow.ui.model.FlowRunHistoryListModel;
 import haflow.ui.model.FlowRunHistoryModel;
 
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
 import java.util.List;
 import java.util.Set;
 import java.util.UUID;
@@ -39,6 +41,19 @@ public class RunHistoryHelper {
 			frhm.setTimestamp(feh.getTimestamp());
 			flowHistorys.add(frhm);
 		}
+		Collections.sort(flowHistorys, new Comparator<FlowRunHistoryModel>(){
+			public int compare(FlowRunHistoryModel o1, FlowRunHistoryModel o2) {
+				if( o1 == o2) return 0;
+				FlowRunHistoryModel f1 = (FlowRunHistoryModel)o1;
+				FlowRunHistoryModel f2 = (FlowRunHistoryModel)o2;
+				if( f1.getTimestamp().before(f2.getTimestamp())){
+					return 1;
+				}else if(f1.getTimestamp().after(f2.getTimestamp()) ){
+					return -1;
+				}
+				return 0;
+			}
+		});
 		FlowRunHistoryListModel frhlm = new FlowRunHistoryListModel();
 		frhlm.setFlowHistorys(flowHistorys);
 		return frhlm;
diff --git a/src/main/webapp/script/haflow.main.js b/src/main/webapp/script/haflow.main.js
index c71eb09..6b00ad6 100644
--- a/src/main/webapp/script/haflow.main.js
+++ b/src/main/webapp/script/haflow.main.js
@@ -180,7 +180,7 @@ HAFlow.Main.prototype.runFlow = function(flowId) {
 				data : JSON.stringify({}),
 				success : function(data, status) {
 					HAFlow.showDialog("Run Flow", " Commited: " + data.commited
-							+ "\n" + "Result: " + data.message);
+							+ "<br>" + "Message:<br> " + data.message);
 				},
 				error : function(request, status, error) {
 					HAFlow.showDialog("Error",