Perl extension for simple-minded recipe-controlled build of data

 Data::Flow allows you to define recipes for building data. A recipe
 contains all of the rules for determining the value of the data involved
 based on a set of defaults and/or interreactions with other pieces of
 data in an automated fashion. You can define any or all of:
  - default values
  - prerequisites (other fields that must have values before the field
    in question can be determined)
  - subroutines to build the field data given all requirements