Grid-Flow is a scientific workflow infrastructure that assists researchers in specifying scientific experiments using a Petri-net-based interface. The contributions of Grid-Flow are as follows: (1) a new, lightweight, programmable Grid workflow language, Grid-Flow Description Language (GFDL), to describe the workflow process in a Grid environment; (2) a Petri-net-based user interface, based on the Generic Modeling Environment, to help the user design the workflow process with a Petri-net model; and (3) a program integration component of the Grid-Flow system to integrate all possible programs into the system.