rdf-ex/lib/rdf/quad.ex

109 lines
4.1 KiB
Elixir

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