       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.
