from langgraph.graph import StateGraph, add_edge

def extract_task(input_state):
    # Extraction using GPT instructions, passing schema in state
    ...

def transform_task(input_state):
    # Data transformation with explicit downstream links
    ...

graph = StateGraph()
graph.add_node('extract', extract_task)
graph.add_node('transform', transform_task)
add_edge(graph, 'extract', 'transform')
graph.set_entry_node('extract')

output = graph.run({'source': 'postgresql', 'target': 'bigquery'})