Subgraphs with no edge connected to the SubgraphInput component do not declare any input ports, therefore cannot receive input data so will likely be used as Readers.
Figure 46.1. Subgraph - Reader
Subgraphs with no edge connected to the SubgraphOutput component provide no output ports, therefore cannot produce any data so will likely be used as Writers.
Figure 46.2. Subgraph - Writer
Subgraph having connected both components (SubgraphInput and SubgraphOutput) is essentially a Transformer.
Figure 46.3. Subgraph - Transformer
Subgraphs with no edge connected to the SubgraphInput or SubgraphOutput components can be used as utility Executors. As they cannot be connected to other components in a parent graph, the execution of subgraphs without ports is controlled via Phases.
Figure 46.4. Subgraph - Executor