Why Control Flow?

• Some workflows have dynamic inputs and multiple branches
• Data may update frequently, and certain settings can change over time
• In some cases a workflow may have branches and a rule that determines which branch to follow
• Therefore, effective workflow control is essential

How is Flow Control Achieved?

• Workflows can be controlled by:
  • parametrizing settings using flow variables
  • repeating a part of the workflow for different inputs
  • defining a rule to activate a branch
  • providing an error handling branch if node execution fails

Flow Control Nodes

• KNIME offers many flow control nodes
• In the Classic UI, these are displayed under various categories

What are Flow Variables?

• Flow variables are parameters with string, integer, double, array, or path values
• They allow avoiding manual node setting changes during new executions with different settings
• Flow variables are accessible only by downstream nodes in the workflow

How are Flow Variables Created?

• The first row (column names) of a table can be converted into flow variables
• Node configurations can be exported as flow variables
• Flow variables can be created using Configuration and Widget nodes
• New flow variables can be generated by combining or modifying existing ones

Flow Variables Ports

• Flow variable ports are two red circles above each node
• Variable Inport is on the top left corner
• Variable Outport is on the top right corner

Making Flow Variable Ports Visible

• Usually hidden, but visible in Modern UI by hovering over the corners of a node
• In Classic UI, make them visible by right-clicking and selecting Show Flow Variable Ports
• These ports allow passing variables between nodes

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