DMReader and DMWriter elements read and write
values to and from various data sources. Currently the console and files are
supported, and in the future support may be added for RDBMS and Java objects
(via reflection).
Stream readers and writers read and write a stream (for example, the
System.out in Java. They have a string attribute named stream
that defines the stream. Values for accessing the console are
stdin, stdout, and stderr.
File readers and writers read and write a file. They have an attribute named
path that is the path to the file.