Camunda Example clarification - camunda

Question

Am new to Camunda when am developing the camunda process flow in usertask am assign the assignee through properties but it not assign to particular user.
and am worked on ubuntu 14.0.4 and camunda with BPMN 2.0 first example am trying.
Can any one help me? And one more clarification if we are create the Html forms and its also not reflect when we start the process with credentials demo/demo and when include the service task binding with class in .bpmn file
and am facing the following error in tomcat log file:
I am working on following environment:
OS:ubuntu14.0.4
Eclipse:Luna
jdk:1.8
tomcat:7
Camunda:Camunda BPM platform v7.3.0.
am trying to execute the following example
"https://docs.camunda.org/get-started/bpmn20/deploy/"
and this is my bpmn file:
SequenceFlow_1
SequenceFlow_7
SequenceFlow_1
SequenceFlow_7
SequenceFlow_8
SequenceFlow_8
SEVERE: Exception sending context initialized event to listener instance of class org.camunda.bpm.getstarted.loanapproval.LoanApprovalApplication
org.camunda.bpm.engine.ProcessEngineException: Exception while performing 'Deployment of Process Application Loan Approval App => Deployment of process archive 'loan-approval': One of the attributes 'class', 'delegateExpression', 'type', or 'expression' is mandatory on serviceTask. | loan-approval.bpmn | line 17 | column 150
at org.camunda.bpm.container.impl.spi.DeploymentOperation.execute(DeploymentOperation.java:134)
at org.camunda.bpm.container.impl.jmx.MBeanServiceContainer.executeDeploymentOperation(MBeanServiceContainer.java:148)
at org.camunda.bpm.container.impl.spi.DeploymentOperation$DeploymentOperationBuilder.execute(DeploymentOperation.java:209)
at org.camunda.bpm.container.impl.RuntimeContainerDelegateImpl.deployProcessApplication(RuntimeContainerDelegateImpl.java:87)
at org.camunda.bpm.application.AbstractProcessApplication.deploy(AbstractProcessApplication.java:51)
at org.camunda.bpm.application.impl.ServletProcessApplication.contextInitialized(ServletProcessApplication.java:131)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:5014)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5528)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:652)
at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:1095)
at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1930)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.camunda.bpm.engine.ProcessEngineException: One of the attributes 'class', 'delegateExpression', 'type', or 'expression' is mandatory on serviceTask. | loan-approval.bpmn | line 17 | column 150
at org.camunda.bpm.engine.impl.util.xml.Parse.throwExceptionForErrors(Parse.java:188)
at org.camunda.bpm.engine.impl.bpmn.parser.BpmnParse.execute(BpmnParse.java:267)
at org.camunda.bpm.engine.impl.bpmn.deployer.BpmnDeployer.deploy(BpmnDeployer.java:105)
at org.camunda.bpm.engine.impl.persistence.deploy.DeploymentCache$1.call(DeploymentCache.java:62)
at org.camunda.bpm.engine.impl.persistence.deploy.DeploymentCache$1.call(DeploymentCache.java:59)
at org.camunda.bpm.engine.impl.interceptor.CommandContext.runWithoutAuthorization(CommandContext.java:485)
at org.camunda.bpm.engine.impl.persistence.deploy.DeploymentCache.deploy(DeploymentCache.java:59)
at org.camunda.bpm.engine.impl.persistence.entity.DeploymentManager.insertDeployment(DeploymentManager.java:47)
at org.camunda.bpm.engine.impl.cmd.DeployCmd.deploy(DeployCmd.java:177)
at org.camunda.bpm.engine.impl.cmd.DeployCmd$1.call(DeployCmd.java:93)
at org.camunda.bpm.engine.impl.cmd.DeployCmd$1.call(DeployCmd.java:82)
at org.camunda.bpm.engine.impl.interceptor.CommandContext.runWithoutAuthorization(CommandContext.java:485)

Answer 1

The new Camunda Modeler produces BPMN models that require Camunda version >= 7.4.0, 7.3.3, 7.2.6 to run (see https://docs.camunda.org/manual/latest/modeler/).
The reason is that the namespace for Camunda extension elements and attributes has changed from http://activiti.org/bpmn to http://camunda.org/schema/1.0/bpmn. The new modeler produces models that use the new namespace and that can therefore not be executed on Camunda platform versions that don't support it. Assuming that you use this modeler, you'll have to upgrade Camunda.
As an alternative, you can use the deprecated Eclipse plugin. Again, make sure to choose the correct version that works with 7.3.0.