118 lines
5 KiB
Elixir
118 lines
5 KiB
Elixir
defmodule RDF.Statement do
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@moduledoc """
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Helper functions for RDF statements.
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A RDF statement is either a `RDF.Triple` or a `RDF.Quad`.
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"""
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alias RDF.{Triple, Quad, IRI, BlankNode, Literal}
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@type subject :: IRI.t | BlankNode.t
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@type predicate :: IRI.t
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@type object :: IRI.t | BlankNode.t | Literal.t
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@type graph_name :: IRI.t | BlankNode.t
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@type coercible_subject :: subject | atom | String.t
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@type coercible_predicate :: predicate | atom | String.t
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@type coercible_object :: object | atom | String.t # TODO: all basic Elixir types coercible to Literals
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@type coercible_graph_name :: graph_name | atom | String.t
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@doc """
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Creates a `RDF.Statement` tuple 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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## Examples
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iex> RDF.Statement.coerce {"http://example.com/S", "http://example.com/p", 42}
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{~I<http://example.com/S>, ~I<http://example.com/p>, RDF.literal(42)}
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iex> RDF.Statement.coerce {"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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"""
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def coerce(statement)
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def coerce({_, _, _} = triple), do: Triple.new(triple)
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def coerce({_, _, _, _} = quad), do: Quad.new(quad)
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@doc false
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def coerce_subject(iri)
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def coerce_subject(iri = %IRI{}), do: iri
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def coerce_subject(bnode = %BlankNode{}), do: bnode
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def coerce_subject("_:" <> identifier), do: RDF.bnode(identifier)
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def coerce_subject(iri) when is_atom(iri) or is_binary(iri), do: RDF.iri!(iri)
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def coerce_subject(arg), do: raise RDF.Triple.InvalidSubjectError, subject: arg
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@doc false
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def coerce_predicate(iri)
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def coerce_predicate(iri = %IRI{}), do: iri
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# Note: Although, RDF does not allow blank nodes for properties, JSON-LD allows
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# them, by introducing the notion of "generalized RDF".
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# TODO: Support an option `:strict_rdf` to explicitly disallow them or produce warnings or ...
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def coerce_predicate(bnode = %BlankNode{}), do: bnode
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def coerce_predicate(iri) when is_atom(iri) or is_binary(iri), do: RDF.iri!(iri)
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def coerce_predicate(arg), do: raise RDF.Triple.InvalidPredicateError, predicate: arg
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@doc false
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def coerce_object(iri)
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def coerce_object(iri = %IRI{}), do: iri
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def coerce_object(literal = %Literal{}), do: literal
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def coerce_object(bnode = %BlankNode{}), do: bnode
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def coerce_object(bool) when is_boolean(bool), do: Literal.new(bool)
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def coerce_object(atom) when is_atom(atom), do: RDF.iri(atom)
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def coerce_object(arg), do: Literal.new(arg)
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@doc false
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def coerce_graph_name(iri)
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def coerce_graph_name(nil), do: nil
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def coerce_graph_name(iri = %IRI{}), do: iri
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def coerce_graph_name(bnode = %BlankNode{}), do: bnode
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def coerce_graph_name("_:" <> identifier), do: RDF.bnode(identifier)
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def coerce_graph_name(iri) when is_atom(iri) or is_binary(iri), do: RDF.iri!(iri)
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def coerce_graph_name(arg),
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do: raise RDF.Quad.InvalidGraphContextError, graph_context: arg
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@doc """
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Returns a tuple of native Elixir values from a `RDF.Statement` 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.Statement.values {~I<http://example.com/S>, ~I<http://example.com/p>, RDF.literal(42)}
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{"http://example.com/S", "http://example.com/p", 42}
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iex> RDF.Statement.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.Statement.values(fn
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...> {:subject, subject} ->
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...> subject |> to_string() |> String.last()
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...> {:predicate, predicate} ->
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...> predicate |> to_string() |> String.last() |> String.to_atom()
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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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...> end)
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{"S", :p, 42, ~I<http://example.com/Graph>}
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"""
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def values(statement, mapping \\ &default_term_mapping/1)
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def values({_, _, _} = triple, mapping), do: RDF.Triple.values(triple, mapping)
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def values({_, _, _, _} = quad, mapping), do: RDF.Quad.values(quad, mapping)
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def values(_, _), do: nil
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@doc false
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def default_term_mapping(qualified_term)
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def default_term_mapping({:graph_name, nil}), do: nil
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def default_term_mapping({_, term}), do: RDF.Term.value(term)
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end
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