Add RDF.Query.BGP builder
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Marcel Otto
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f9e451f006
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3 changed files with 307 additions and 0 deletions
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@ -54,3 +54,8 @@ end
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defmodule RDF.Namespace.UndefinedTermError do
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defexception [:message]
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end
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defmodule RDF.Query.InvalidError do
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defexception [:message]
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end
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@ -2,6 +2,9 @@ defmodule RDF.Query.BGP do
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@enforce_keys [:triple_patterns]
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defstruct [:triple_patterns]
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alias RDF.{IRI, BlankNode, Literal, Namespace}
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import RDF.Utils.Guards
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@type variable :: String.t
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@type triple_pattern :: {
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subject :: variable | RDF.Term.t,
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@ -13,6 +16,151 @@ defmodule RDF.Query.BGP do
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@type t :: %__MODULE__{triple_patterns: triple_patterns}
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def new(query) do
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case new!(query) do
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{:ok, bgp} -> bgp
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{:error, error} -> raise error
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end
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end
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def new!(query) do
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with {:ok, triple_patterns} <- triple_patterns(query) do
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{:ok, %__MODULE__{triple_patterns: triple_patterns}}
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end
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end
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defp triple_patterns(query) when is_list(query) do
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Enum.reduce_while(query, {:ok, []}, fn
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triple, {:ok, triple_patterns} ->
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case triple_pattern(triple) do
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{:ok, triple_pattern} ->
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{:cont, {:ok, triple_patterns ++ List.wrap(triple_pattern)}}
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{:error, error} ->
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{:halt, {:error, error}}
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end
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end)
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end
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defp triple_patterns(triple_pattern) when is_tuple(triple_pattern),
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do: triple_patterns([triple_pattern])
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defp triple_pattern({subject, predicate, object})
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when not is_list(predicate) and not is_list(object) do
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with {:ok, subject_pattern} <- subject_pattern(subject),
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{:ok, predicate_pattern} <- predicate_pattern(predicate),
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{:ok, object_pattern} <- object_pattern(object) do
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{:ok, {subject_pattern, predicate_pattern, object_pattern}}
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end
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end
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defp triple_pattern(combined_objects_triple_pattern) when is_tuple(combined_objects_triple_pattern) do
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[subject | rest] = Tuple.to_list(combined_objects_triple_pattern)
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case rest do
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[predicate | objects] when not is_list(predicate) ->
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if Enum.all?(objects, &(not is_list(&1))) do
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objects
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|> Enum.map(fn object -> {subject, predicate, object} end)
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|> triple_patterns()
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else
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{:error, %RDF.Query.InvalidError{
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message: "Invalid use of predicate-object pair brackets"}
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}
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end
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predicate_object_pairs ->
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if Enum.all?(predicate_object_pairs, &(is_list(&1) and length(&1) > 1)) do
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predicate_object_pairs
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|> Enum.flat_map(fn [predicate | objects] ->
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Enum.map(objects, fn object -> {subject, predicate, object} end)
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end)
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|> triple_patterns()
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else
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{:error, %RDF.Query.InvalidError{
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message: "Invalid use of predicate-object pair brackets"}
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}
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end
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end
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end
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defp subject_pattern(subject) do
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value = variable(subject) || resource(subject)
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if value do
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{:ok, value}
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else
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{:error, %RDF.Query.InvalidError{
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message: "Invalid subject term in BGP triple pattern: #{inspect subject}"}
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}
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end
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end
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defp predicate_pattern(predicate) do
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value = variable(predicate) || resource(predicate) || property(predicate)
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if value do
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{:ok, value}
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else
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{:error, %RDF.Query.InvalidError{
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message: "Invalid predicate term in BGP triple pattern: #{inspect predicate}"}
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}
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end
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end
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defp object_pattern(object) do
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value = variable(object) || resource(object) || literal(object)
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if value do
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{:ok, value}
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else
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{:error, %RDF.Query.InvalidError{
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message: "Invalid object term in BGP triple pattern: #{inspect object}"}
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}
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end
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end
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defp variable(var) when is_atom(var) do
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var_string = to_string(var)
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if String.ends_with?(var_string, "?") do
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var_string
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|> String.slice(0..-2)
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|> String.to_atom()
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end
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end
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defp variable(_), do: nil
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defp resource(%IRI{} = iri), do: iri
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defp resource(%URI{} = uri), do: IRI.new(uri)
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defp resource(%BlankNode{} = bnode), do: bnode
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defp resource(var) when is_ordinary_atom(var) do
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case to_string(var) do
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"_" <> bnode ->
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BlankNode.new(bnode)
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_ ->
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case Namespace.resolve_term(var) do
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{:ok, iri} -> iri
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_ -> nil
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end
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end
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end
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defp resource(_), do: nil
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defp property(:a), do: RDF.type()
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defp property(_), do: nil
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defp literal(%Literal{} = literal), do: literal
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defp literal(value), do: Literal.coerce(value)
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@doc """
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Return a list of all variables in a BGP.
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"""
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def variables(%__MODULE__{triple_patterns: triple_patterns}), do: variables(triple_patterns)
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def variables(triple_patterns) when is_list(triple_patterns) do
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154
test/unit/query/bgp_test.exs
Normal file
154
test/unit/query/bgp_test.exs
Normal file
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@ -0,0 +1,154 @@
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defmodule RDF.Query.BGPTest do
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use RDF.Test.Case
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alias RDF.Query.BGP
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defp bgp(triple_patterns) when is_list(triple_patterns),
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do: %BGP{triple_patterns: triple_patterns}
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describe "new/1" do
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test "empty triple pattern" do
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assert BGP.new([]) == bgp([])
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end
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test "one triple pattern doesn't require list brackets" do
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assert BGP.new({EX.s, EX.p, EX.o}) ==
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bgp [{EX.s, EX.p, EX.o}]
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end
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test "variables" do
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assert BGP.new([{:s?, :p?, :o?}]) == bgp [{:s, :p, :o}]
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end
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test "blank nodes" do
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assert BGP.new([{RDF.bnode("s"), RDF.bnode("p"), RDF.bnode("o")}]) ==
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bgp [{RDF.bnode("s"), RDF.bnode("p"), RDF.bnode("o")}]
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end
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test "blank nodes as atoms" do
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assert BGP.new([{:_s, :_p, :_o}]) ==
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bgp [{RDF.bnode("s"), RDF.bnode("p"), RDF.bnode("o")}]
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end
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test "variable notation has precedence over blank node notation" do
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assert BGP.new([{:_s?, :_p?, :_o?}]) == bgp [{:_s, :_p, :_o}]
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end
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test "IRIs" do
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assert BGP.new([{
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RDF.iri("http://example.com/s"),
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RDF.iri("http://example.com/p"),
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RDF.iri("http://example.com/o")}]
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) == bgp [{EX.s, EX.p, EX.o}]
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assert BGP.new([{
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~I<http://example.com/s>,
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~I<http://example.com/p>,
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~I<http://example.com/o>}]
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) == bgp [{EX.s, EX.p, EX.o}]
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assert BGP.new([{EX.s, EX.p, EX.o}]) ==
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bgp [{EX.s, EX.p, EX.o}]
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end
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test "vocabulary term atoms" do
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assert BGP.new([{EX.S, EX.P, EX.O}]) ==
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bgp [{RDF.iri(EX.S), RDF.iri(EX.P), RDF.iri(EX.O)}]
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end
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test "special :a atom for rdf:type" do
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assert BGP.new([{EX.S, :a, EX.O}]) ==
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bgp [{RDF.iri(EX.S), RDF.type, RDF.iri(EX.O)}]
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end
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test "URIs" do
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assert BGP.new([{
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URI.parse("http://example.com/s"),
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URI.parse("http://example.com/p"),
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URI.parse("http://example.com/o")}]
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) == bgp [{EX.s, EX.p, EX.o}]
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end
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test "literals" do
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assert BGP.new([{EX.s, EX.p, ~L"foo"}]) ==
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bgp [{EX.s, EX.p, ~L"foo"}]
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end
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test "values coercible to literals" do
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assert BGP.new([{EX.s, EX.p, "foo"}]) ==
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bgp [{EX.s, EX.p, ~L"foo"}]
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assert BGP.new([{EX.s, EX.p, 42}]) ==
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bgp [{EX.s, EX.p, RDF.literal(42)}]
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assert BGP.new([{EX.s, EX.p, true}]) ==
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bgp [{EX.s, EX.p, XSD.true}]
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end
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test "literals on non-object positions" do
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assert_raise RDF.Query.InvalidError, fn ->
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assert BGP.new([{~L"foo", EX.p, ~L"bar"}])
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end
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end
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test "multiple triple patterns" do
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assert BGP.new([
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{EX.S, EX.p, :o?},
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{:o?, EX.p2, 42}
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]) ==
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bgp [
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{RDF.iri(EX.S), EX.p, :o},
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{:o, EX.p2, RDF.literal(42)}
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]
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end
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test "multiple objects to the same subject-predicate" do
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assert BGP.new([{EX.s, EX.p, EX.o1, EX.o2}]) ==
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bgp [
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{EX.s, EX.p, EX.o1},
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{EX.s, EX.p, EX.o2}
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]
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assert BGP.new({EX.s, EX.p, EX.o1, EX.o2}) ==
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bgp [
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{EX.s, EX.p, EX.o1},
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{EX.s, EX.p, EX.o2}
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]
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assert BGP.new({EX.s, EX.p, :o?, false, 42, "foo"}) ==
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bgp [
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{EX.s, EX.p, :o},
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{EX.s, EX.p, XSD.false},
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{EX.s, EX.p, RDF.literal(42)},
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{EX.s, EX.p, RDF.literal("foo")}
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]
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end
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test "multiple predicate-object pairs to the same subject" do
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assert BGP.new([{
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EX.s,
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[EX.p1, EX.o1],
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[EX.p2, EX.o2],
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}]) ==
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bgp [
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{EX.s, EX.p1, EX.o1},
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{EX.s, EX.p2, EX.o2}
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]
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assert BGP.new([{
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EX.s,
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[:a, :o?],
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[EX.p1, 42, 3.14],
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[EX.p2, "foo", true],
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}]) ==
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bgp [
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{EX.s, RDF.type, :o},
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{EX.s, EX.p1, RDF.literal(42)},
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{EX.s, EX.p1, RDF.literal(3.14)},
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{EX.s, EX.p2, RDF.literal("foo")},
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{EX.s, EX.p2, XSD.true}
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]
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assert BGP.new([{EX.s, [EX.p, EX.o]}]) ==
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bgp [{EX.s, EX.p, EX.o}]
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end
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end
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end
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