If a relative filename is specified, the BIS service attempts to locate a data file by searching the directories specified by the FILE_PREFIX environment variable and a program object file by searching the CODE_PREFIX environment variable. For full details of how the BIS service program locates files, see Code and Data File Search Paths of the ACUCOBOL-GT User's Guide.
Note that the RunPath tag may be used to insert additional directories before the default FILE_PREFIX and CODE_PREFIX variables from the environment. Also note that this will override the contents of the FILE_PREFIX and CODE_PREFIX configuration variables, so use of the RunPath tag is discouraged.