What a derived source's stored function calls to reach the registered operations (spec/04 §6): an aggregate of values, or a transform over rows, by name, with the options a design's node would carry.

fn %{hosts: rows} ->
  p95 = rows |> Enum.map(& &1.cpu) |> Macaw.Data.Ops.aggregate("quantile", %{p: 0.95})

  rows
  |> Macaw.Data.Ops.transform("filter", %{field: "cpu", test: :gte, value: p95})
  |> Macaw.Data.Ops.transform("sort", %{field: "cpu", order: :descending})
end

In a stored function the name is a literal string the checker holds to the engine's registry, and the call is compiled against that registry (__run__/5), so it runs exactly what was checked. Called from a host's own code, the functions use macaw_data's own package. A fault in the options raises ArgumentError with Macaw.Data.Operations.format_error/1's words.

iex> Macaw.Data.Ops.aggregate([3, nil, 1, 2], "median")
2
iex> Macaw.Data.Ops.transform([%{v: 2}, %{v: 1}], "sort", %{field: :v})
[%{v: 1}, %{v: 2}]