gistfile1.txt

class Base
  something_something :mappings
  self.mappings = {}
end

class FirstChild < Base
  self.mappings[:foo] = :bar
end

class SecondChild < Base
  self.mappings[:foo] = :baz
end

Base.mappings           # {}
FirstChild.mappings     # {:foo=>:bar}
SecondChild.mappings    # {:foo=>:baz}