44 lines
1.3 KiB
Elixir
44 lines
1.3 KiB
Elixir
defmodule RDF.Query.BGP.QueryPlanner do
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@moduledoc false
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alias RDF.Query.BGP
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def query_plan(triple_patterns, solved \\ [], plan \\ [])
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def query_plan([], _, plan), do: Enum.reverse(plan)
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def query_plan(triple_patterns, solved, plan) do
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[next_best | rest] = Enum.sort_by(triple_patterns, &triple_priority/1)
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new_solved = Enum.uniq(BGP.variables(next_best) ++ solved)
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query_plan(
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mark_solved_variables(rest, new_solved),
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new_solved,
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[next_best | plan]
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)
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end
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defp triple_priority({v, v, v}), do: triple_priority({v, "p", "o"})
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defp triple_priority({v, v, o}), do: triple_priority({v, "p", o})
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defp triple_priority({v, p, v}), do: triple_priority({v, p, "o"})
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defp triple_priority({s, v, v}), do: triple_priority({s, v, "o"})
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defp triple_priority({s, p, o}) do
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{sp, pp, op} = {value_priority(s), value_priority(p), value_priority(o)}
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<<sp + pp + op::size(2), sp::size(1), pp::size(1), op::size(1)>>
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end
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defp value_priority(value) when is_atom(value), do: 1
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defp value_priority(_), do: 0
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defp mark_solved_variables(triple_patterns, solved) do
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Enum.map(triple_patterns, fn {s, p, o} ->
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{
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if(is_atom(s) and s in solved, do: {s}, else: s),
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if(is_atom(p) and p in solved, do: {p}, else: p),
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if(is_atom(o) and o in solved, do: {o}, else: o)
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}
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end)
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end
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end
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