AWS SDK for .NET Documentation
WorkflowId Property
AmazonAmazon.SimpleWorkflow.ModelStartWorkflowExecutionRequestWorkflowId Did this page help you?   Yes   No    Tell us about it...
The user defined identifier associated with the workflow execution. You can use this to associate a custom identifier with the workflow execution. You may specify the same identifier if a workflow execution is logically a restart of a previous execution. You cannot have two open workflow executions with the same workflowId at the same time. The specified string must not start or end with whitespace. It must not contain a : (colon), / (slash), | (vertical bar), or any control characters (\u0000-\u001f | \u007f - \u009f). Also, it must not contain the literal string "arn".

Constraints:

Length
1 - 256

Declaration Syntax
C#
public string WorkflowId { get; set; }

Assembly: AWSSDK (Module: AWSSDK) Version: 1.5.60.0 (1.5.60.0)