Debugging a graph

In certain aspects, a method includes: receiving a first graph that includes components and flows, the components representing operations performed on data records, the flows representing flows of data records between components; receiving a specification that is separate from the first graph, the specification defining one or more insertions, each of the insertions associated with a flow of the first graph; generating one or more components that each corresponds to one of the insertions; and generating a second graph that includes components and flows that correspond to at least some of the components and flows of the first graph and the one or more generated components.