The project, PE_Backward_Forward_Schema_Propagation, demonstrates the PipeLine Execute Snap's capability of propagating schema in both directions – upstream and downstream. It contains the following Pipelines:

• PE_Backward_Forward_Schema_Propagation_Parent

• PE_Backward_Forward_Schema_Propagation_Child

The parent Pipeline is as shown below:

example-backward-forward-schema-propagation-parent.slp

The child Pipeline is as shown below:

Child pipeline image

example-backward-forward-schema-propagation-child.slp

The PipeLine Execute Snap is configured to call the Pipeline schema-child. This child Pipeline consists of a Mapper Snap that is configured as shown below:

The Mapper Snaps upstream and downstream of the PipeLine Execute Snap: Mapper_InputSchemaPropagation and Mapper_TargetSchemaPropagation are configured as shown below:

When the Pipeline is executed, data propagation takes place between the parent and child Pipeline:

• The string expression $foo is propagated from the child Pipeline to the PipeLine Execute Snap.

• The PipeLine Execute Snap propagates it to the upstream Mapper Snap (Mapper_InputSchemaPropagation), as visible in the Target Schema section. Here it is assigned the value 123.

• This is passed from the Mapper to the PipeLine Execute Snap, which internally passes the value to the child Pipeline. Here, $foo is mapped to $bar. $baz is another string expression in the child Pipeline (assigned the value 2).

• $bar, and $baz are propagated to the PipeLine Execute Snap and propagated forward to the downstream Mapper Snap (Mapper_TargetSchemaPropagation). This can be seen in the Input Schema section of the Mapper Snap.