The operation of a data flow is improved by providing for validation of the consistency of the data flow with the external data files it works with, even in the face of changes in those external data files Metadata is stored regarding the external data files. Because external data files may change, this metadata is used when determining whether the external data files are still compatible with the data flow. In such performing such validation, the metadata tracks what changes in the external data files have occurred, and allows increased flexibility in presenting the user with options or in automatically fixing the data flow to correspond with changes in external data files. When the external data files are not available, the stored metadata can be used to validate the data flow to the last information regarding the external data files. The external metadata can be resynchronized to the data flow or to the external data files to provide updated external metadata for later validation.