def tuple(heading, name = nil, metadata = nil)
      heading = heading(heading)
      name    = name(name)
      meta    = metadata(metadata)

      TupleType.new(heading, name, meta)
    end
def tuple(heading, name = nil, metadata = nil)
      heading = heading(heading)
      name    = name(name)
      meta    = metadata(metadata)

      TupleType.new(heading, name, meta)
    end
Tuples and relations