The module Data::Flow provides its services via objects.  The objects
may be obtained by the usual

         $request = new Data::Flow $recipes;

paradigm. The argument $recipes is a hash reference, which provides the
rules for request processing. The objects support two methods, set() and
get(). The first one is used to provide input data for processing, the
second one to obtain the output.

The unit of requested information is a field. The method set() takes a
pair field => value, the method get() takes one argument: the field.

Every object is created without any fields filled, but it knows how to
construct fields basing on other fields or some global into. This
knowledge is provided in the argument $recipe of the new() function.
This is a reference to a hash, keyed by fields. The values of this hash
are hash references themselves, which describe how to acquire the field
which is the corresponding key of the initial hash.

WWW: https://metacpan.org/release/Data-Flow