1. A method of debugging a data flow associated with an extract, transform and load (ETL) process, the method comprising: providing a user with a graphical representation of an ETL job, said graphical representation comprising individualized representations of one or more data sources, data destinations, and transform operations on data flowing from a data source to a data destination; receiving a user selection of a subset of said transform operations; providing the user with a selection menu for selecting one or more boundary conditions of the selected subset of transform operations, the boundary conditions comprising a set of replacement options for replacing the data source in the debug process, the replacement options comprising a source for generating random data for the selected transform operation and a source data file pointing to a defined location; and generating an execution script based on the received subset and the boundary conditions.