109 lines
4.1 KiB
Elixir
109 lines
4.1 KiB
Elixir
defmodule RDF.Quad do
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@moduledoc """
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Helper functions for RDF quads.
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A RDF Quad is represented as a plain Elixir tuple consisting of four valid
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RDF values for subject, predicate, object and a graph context.
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"""
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alias RDF.Statement
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@doc """
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Creates a `RDF.Quad` with proper RDF values.
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An error is raised when the given elements are not coercible to RDF values.
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Note: The `RDF.quad` function is a shortcut to this function.
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## Examples
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iex> RDF.Quad.new("http://example.com/S", "http://example.com/p", 42, "http://example.com/Graph")
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{~I<http://example.com/S>, ~I<http://example.com/p>, RDF.literal(42), ~I<http://example.com/Graph>}
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iex> RDF.Quad.new(EX.S, EX.p, 42, EX.Graph)
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{RDF.iri("http://example.com/S"), RDF.iri("http://example.com/p"), RDF.literal(42), RDF.iri("http://example.com/Graph")}
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"""
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def new(subject, predicate, object, graph_context) do
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{
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Statement.coerce_subject(subject),
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Statement.coerce_predicate(predicate),
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Statement.coerce_object(object),
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Statement.coerce_graph_name(graph_context)
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}
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end
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@doc """
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Creates a `RDF.Quad` with proper RDF values.
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An error is raised when the given elements are not coercible to RDF values.
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Note: The `RDF.quad` function is a shortcut to this function.
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## Examples
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iex> RDF.Quad.new {"http://example.com/S", "http://example.com/p", 42, "http://example.com/Graph"}
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{~I<http://example.com/S>, ~I<http://example.com/p>, RDF.literal(42), ~I<http://example.com/Graph>}
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iex> RDF.Quad.new {EX.S, EX.p, 42, EX.Graph}
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{RDF.iri("http://example.com/S"), RDF.iri("http://example.com/p"), RDF.literal(42), RDF.iri("http://example.com/Graph")}
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"""
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def new({subject, predicate, object, graph_context}),
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do: new(subject, predicate, object, graph_context)
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@doc """
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Returns a tuple of native Elixir values from a `RDF.Quad` of RDF terms.
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Returns `nil` if one of the components of the given tuple is not convertible via `RDF.Term.value/1`.
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The optional second argument allows to specify a custom mapping with a function
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which will receive a tuple `{statement_position, rdf_term}` where
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`statement_position` is one of the atoms `:subject`, `:predicate`, `:object` or
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`:graph_name`, while `rdf_term` is the RDF term to be mapped. When the given
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function returns `nil` this will be interpreted as an error and will become
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the overhaul result of the `values/2` call.
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## Examples
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iex> RDF.Quad.values {~I<http://example.com/S>, ~I<http://example.com/p>, RDF.literal(42), ~I<http://example.com/Graph>}
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{"http://example.com/S", "http://example.com/p", 42, "http://example.com/Graph"}
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iex> {~I<http://example.com/S>, ~I<http://example.com/p>, RDF.literal(42), ~I<http://example.com/Graph>}
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...> |> RDF.Quad.values(fn
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...> {:object, object} ->
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...> RDF.Term.value(object)
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...> {:graph_name, graph_name} ->
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...> graph_name
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...> {_, resource} ->
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...> resource |> to_string() |> String.last() |> String.to_atom()
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...> end)
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{:S, :p, 42, ~I<http://example.com/Graph>}
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"""
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def values(quad, mapping \\ &Statement.default_term_mapping/1)
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def values({subject, predicate, object, graph_context}, mapping) do
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with subject_value when not is_nil(subject_value) <- mapping.({:subject, subject}),
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predicate_value when not is_nil(predicate_value) <- mapping.({:predicate, predicate}),
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object_value when not is_nil(object_value) <- mapping.({:object, object}),
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graph_context_value <- mapping.({:graph_name, graph_context})
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do
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{subject_value, predicate_value, object_value, graph_context_value}
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else
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_ -> nil
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end
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end
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def values(_, _), do: nil
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@doc """
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Checks if the given tuple is a valid RDF quad.
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The elements of a valid RDF quad must be RDF terms. On the subject
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position only IRIs and blank nodes allowed, while on the predicate and graph
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context position only IRIs allowed. The object position can be any RDF term.
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"""
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def valid?(tuple)
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def valid?({_, _, _, _} = quad), do: Statement.valid?(quad)
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def valid?(_), do: false
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end
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