An HDS locator for the data object associated with the specified
parameter is returned. The parameter system will attempt to associate
an object if one is not already associated. This operation is identical
with DAT_ASSOC except under error conditions. When there is an error,
DAT_EXIST reports the error and returns the status value immediately,
whereas DAT_ASSOC repeatedly attempts to get a valid locator.
If the named object does not exist, status PAR__ERROR is returned.
The object will be opened with the appropriate ACCESS mode. If ACCESS
is incompatible with the access mode specified for the parameter in
the program's Interface File, status SUBPAR__ICACM will be returned.