rdf-ex/lib/rdf/statement.ex
2017-06-17 00:27:05 +02:00

74 lines
3 KiB
Elixir

defmodule RDF.Statement do
@moduledoc """
Helper functions for RDF statements.
A RDF statement is either a `RDF.Triple` or a `RDF.Quad`.
"""
alias RDF.{Triple, Quad, BlankNode, Literal}
@type subject :: URI.t | BlankNode.t
@type predicate :: URI.t
@type object :: URI.t | BlankNode.t | Literal.t
@type graph_name :: URI.t | BlankNode.t
@type convertible_subject :: subject | atom | String.t
@type convertible_predicate :: predicate | atom | String.t
@type convertible_object :: object | atom | String.t # TODO: all basic Elixir types convertible to Literals
@type convertible_graph_name :: graph_name | atom | String.t
@doc """
Creates a `RDF.Statement` tuple with proper RDF values.
An error is raised when the given elements are not convertible to RDF values.
## Examples
iex> RDF.Statement.new {"http://example.com/S", "http://example.com/p", 42}
{~I<http://example.com/S>, ~I<http://example.com/p>, RDF.literal(42)}
iex> RDF.Statement.new {"http://example.com/S", "http://example.com/p", 42, "http://example.com/Graph"}
{~I<http://example.com/S>, ~I<http://example.com/p>, RDF.literal(42), ~I<http://example.com/Graph>}
"""
def convert(statement)
def convert({_, _, _} = triple), do: Triple.new(triple)
def convert({_, _, _, _} = quad), do: Quad.new(quad)
@doc false
def convert_subject(uri)
def convert_subject(uri = %URI{}), do: uri
def convert_subject(bnode = %BlankNode{}), do: bnode
def convert_subject("_:" <> identifier), do: RDF.bnode(identifier)
def convert_subject(uri) when is_atom(uri) or is_binary(uri), do: RDF.uri(uri)
def convert_subject(arg), do: raise RDF.Triple.InvalidSubjectError, subject: arg
@doc false
def convert_predicate(uri)
def convert_predicate(uri = %URI{}), do: uri
# Note: Although, RDF does not allow blank nodes for properties, JSON-LD allows
# them, by introducing the notion of "generalized RDF".
# TODO: Support an option `:strict_rdf` to explicitly disallow them or produce warnings or ...
def convert_predicate(bnode = %BlankNode{}), do: bnode
def convert_predicate(uri) when is_atom(uri) or is_binary(uri), do: RDF.uri(uri)
def convert_predicate(arg), do: raise RDF.Triple.InvalidPredicateError, predicate: arg
@doc false
def convert_object(uri)
def convert_object(uri = %URI{}), do: uri
def convert_object(literal = %Literal{}), do: literal
def convert_object(bnode = %BlankNode{}), do: bnode
def convert_object(atom) when is_atom(atom), do: RDF.uri(atom)
def convert_object(arg), do: Literal.new(arg)
@doc false
def convert_graph_name(uri)
def convert_graph_name(nil), do: nil
def convert_graph_name(uri = %URI{}), do: uri
def convert_graph_name(bnode = %BlankNode{}), do: bnode
def convert_graph_name("_:" <> identifier), do: RDF.bnode(identifier)
def convert_graph_name(uri) when is_atom(uri) or is_binary(uri),
do: RDF.uri(uri)
def convert_graph_name(arg),
do: raise RDF.Quad.InvalidGraphContextError, graph_context: arg
end