A Guide to KNIME Flow Control
Dr. Lochana C. Menikarachchi
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