gistfile1.rb

require 'yaml'

yaml = <<YAML
---
default: &default
  a: foo
  b: bar

data1:
  <<: *default

data2:
  <<: *default
  b: BAR
YAML

p YAML.load(yaml)
#=> {"default"=>{"a"=>"foo", "b"=>"bar"}, "data1"=>{"a"=>"foo", "b"=>"bar"}, "data2"=>{"a"=>"foo", "b"=>"BAR"}}