The LEAD event schema currently defines different notification types that are generated during the execution of the workflow. These workflow notifications are used to track the progress of the workflow, to track the provenance of the data products generated from the workflow, and to gather computation time and network latency statistics. The schema file is available at: LEAD Notification Types XSD. Some sample messages using this schema is available in this document. Additional types will be defined in future as the need arises, for e.g. by data mining applications indicate a weather event.

In the section below, workflow engine refers to a BPEL service or Jython script that initiates and controls the workflow. The workflow itself may be represented in BPEL or compiled into a Jython script. Service refers to a web service that usually acts as a wrapper for the user's application code. Application script is the Jython script that stages files and sets up the execution environment, and consumes and produces files on behalf of the user application. User application is the executable that does the real scientific work.

Some of the common fields in the notifications are:

• topic: The notification topic to which this notification being published to.
• WorkflowID: This is a unique string that identifies the workflow instance that is generating this notification. It is currently set to the notification topic for that workflow instance.
• NodeID: This is a string that uniquely identifies the node within the workflow that is generating this notification. This ID is assigned statically when the workflow is composed.
• WorkflowTimestep: The workflow engine maintains a logical clock that monotonically increases with every service invocation by the workflow engine. The workflow timestep field is the timestep of this clock for the current service's invocation. This allows for temporal ordering of the notifications in the absence of a globally synchronized clock..
• ServiceID: The unique QName of the concrete WSDL representing the service instance that is generating this notification.
• timestamp: The timestamp on the client at the moment this notification is generated.
• fileUUID: the LEAD GUID for a logical file that participates in the workflow. The physical file that corresponds to this GUID can be resolved using the LEAD Name Resolver. The actual physical file that caused this notification may be included as a separate field.

WorkflowStart{topic, workflowID, timestamp}

Generated by the workflow engine after the workflow is started and before the first service in the workflow is called.

WorkflowFinishSuccess{topic, workflowID, timestamp}

Generated by the workflow engine after all services in the workflow finish successfully and hence the workflow itself completes successfully.

WorkflowFinishFailed{topic, workflowID, timestamp, errorMessage, stackTrace}

Generated by the workflow engine if any of the services in the workflow fail or if the workflow fails for some other reason and terminates. 'errorMessage' is a human readable description of the error while 'stackTrace' is the stack trace optionally dumped by the faulty region.

InvokeServiceStart{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp}

Generated by the workflow engine before it invokes a service.

InvokeServiceSuccess{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp}

Generated by the workflow engine after the invovation to a service returns successfully.

InvokeServiceFailed{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, errorMessage, stackTrace}

Generated by the workflow engine if the invocation of a service failed. 'errorMessage' is a human readable description of the error while 'stackTrace' is the stack trace optionally dumped by the fault.

ApplicationStart{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, name, host}

Generated by the application script when it is invoked by the service and starts executing. 'name' is a human readable name for the application and 'host' is the hostname for the machine on which the application is executing.

ApplicationFinishSuccess{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, applicationResult}

Generated by the application script when it finishes executing successfully. 'applicationResult' is a list of name-value pairs that are the results of this application, that may be used by successive services as inputs.

ApplicationFinishFailed{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, errorMessage, stackTrace}

Generated by the application script when it terminates executing due to an exception. 'errorMessage' is a human readable description of the error while 'stackTrace' is the stack trace optionally dumped by the faulty section.

ComputationDuration{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, name, durationMillis}

Generated by the application script when it completes executing a particular computation section, possibly the user's application, and the time taken for that section is available. 'name' is a human readable description of the computation section while 'durationMillis' is the time in milliseconds taken by that section.

FileSendDuration & FileReceiveDuration{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, fileUUID, localFilePath, fileSizeBytes, remoteFilePath, durationMillis}

Generated by the application script when it completes sending (receiving) a local file to (from) a remote location, and the time taken for that transfer is available. 'localFilePath' is the absolute path to the local file that is sent (received), 'fileSizeBytes' is the physical size of the transfered file in bytes, 'remoteFilePath' is the remote URL to (from) which the file is sent (received), and 'durationMillis' is the time in milliseconds taken for the transfer.

FileConsumed{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, fileUUID, localFilePath, fileSizeBytes}

Generated by the application script when it uses/consumes a local file for its processing. 'localFilePath' is the absolute path to the local file, and 'fileSizeBytes' is the physical size of the local file.

FileProduced{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, fileUUID, localFilePath, fileSizeBytes}

Generated by the application script when it creates/produces a local file during its execution. 'localFilePath' is the absolute path to the local file generated, and 'fileSizeBytes' is the physical size of the local file.

PublishURL{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, title, location}

Generated by the application script when a file that can be visualized or of special interest is created. This notification usually prompts the notification listener to display the URL as a hyperlink. 'title' is a human readable name or description of the file that can be used as the text for the hyperlink, and 'location' is a URL to which the hyperlink should point.

Log{topic, workflowID, nodeID, wfTimeStep, serviceID, timestamp, message, level}

Generated by the application script when a generic event of interest occurs. This can be used as a general purpose tool for logging that is human understandable. 'message' is the message that is being logged, and 'level' is the granularity or importance of this log message. The levels availabe are INFO, EXCEPTION, WARNING, DEBUG, and these can act as fields on which the log message is filtered by the notification listener.