Vyuh CDX

Appearance

Start & End Nodes ​

Start and End nodes define the entry and terminal points of a workflow.

Start Node ​

Every workflow must have exactly one start node.

Definition ​

dart
builder.start('begin');

// With custom name
builder.start('begin', name: 'Start Order Processing');

Behavior ​

When a workflow starts:

  1. Engine creates a new WorkflowInstance
  2. Creates a token at the start node
  3. Start executor finds the outgoing edge
  4. Returns ContinueResult to move to the next node

Executor ​

dart
class StartNodeExecutor extends NodeExecutor {
  @override
  Future<NodeResult> execute(WorkflowContext context) async {
    final outgoingEdge = context.outgoingEdges.first;
    return ContinueResult.single(outgoingEdge.targetNodeId);
  }
}

End Node ​

Workflows can have multiple end nodes for different outcomes.

Definition ​

dart
// Basic end node
builder.end('completed');

// Named end nodes for different outcomes
builder.end('approved', name: 'Request Approved');
builder.end('rejected', name: 'Request Rejected');
builder.end('cancelled', name: 'Request Cancelled');

Behavior ​

When a token reaches an end node:

  1. End executor returns CompleteWorkflowResult
  2. Token is deactivated
  3. If all tokens are inactive, workflow status becomes completed

Executor ​

dart
class EndNodeExecutor extends NodeExecutor {
  @override
  Future<NodeResult> execute(WorkflowContext context) async {
    return CompleteWorkflowResult(
      output: context.currentNode.config['output'] ?? {},
    );
  }
}

Multiple End Nodes Pattern ​

Use multiple end nodes to represent different workflow outcomes:

dart
final workflow = WorkflowBuilder(...)
    .start('begin')
    .task('validate', ...)
    .oneOf('checkValid', [
      Branch.whenFn((o) => o['isValid'] == true, then: 'process'),
      Branch.otherwise(then: 'invalid'),
    ])
    .task('process', ...)
    .end('success', name: 'Successfully Processed')
    .end('invalid', name: 'Validation Failed')
    .end('error', name: 'Processing Error')
    .connect('begin', 'validate')
    .connect('validate', 'checkValid')
    .connect('process', 'success')
    .build();

Flow Diagram ​

Best Practices ​

1. Name end nodes descriptively ​

dart
// GOOD - Clear outcome names
builder.end('approved', name: 'Request Approved');
builder.end('rejected', name: 'Request Rejected');

// AVOID - Generic names
builder.end('end1');
builder.end('end2');

2. Use a limited number of end nodes ​

A workflow should have 2-4 end nodes representing distinct outcomes:

  • Success path
  • Failure/error path
  • Cancelled/abandoned path
  • Optional: timeout path

3. Ensure all paths lead to end nodes ​

Every possible execution path should terminate at an end node. Use the default branch in gateways to catch unexpected cases.

Next Steps ​