1/*  Part of ClioPatria SeRQL and SPARQL server
    2
    3    Author:        Michiel Hildebrand and Jan Wielemaker
    4    E-mail:        michielh@few.vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2010-2018, E-Culture/MultimediaN
    7                              VU University Amsterdam
    8    All rights reserved.
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   11    modification, are permitted provided that the following conditions
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   15       notice, this list of conditions and the following disclaimer.
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   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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   35
   36:- module(rdf_json,
   37          [ graph_json/2,               % +Graph, -JSON
   38            properties_to_json/2,       % +Pairs:property-values, -JSONList
   39            rdf_object_to_json/2        % +RDFObject, -JSONTerm
   40          ]).   41:- use_module(library(semweb/rdf_db)).   42:- use_module(library(semweb/rdf_describe)).   43:- use_module(library(semweb/rdf_bnode)).   44:- use_module(library(pairs)).   45:- use_module(library(apply)).   46:- use_module(library(assoc)).   47:- use_module(library(http/json)).   48:- use_module(library(http/json_convert)).   49:- use_module(library(http/http_json)).

 graph_json(+Graph, -JSON) is det

JSON is a Prolog JSON object representing Graph.

Arguments:

Graph

- is a list of rdf(S,P,O)

See also

- json_write/3 for serializing JSON

   63graph_json(Graph, json(JSON)) :-
   64    bnode_vars(Graph, Graph1, BNodes),
   65    bnode_ids(BNodes, 1),
   66    map_list_to_pairs(arg(1), Graph1, Pairs),
   67    keysort(Pairs, Pairs1),
   68    group_pairs_by_key(Pairs1, SubjectKeyed),
   69    maplist(json_description, SubjectKeyed, JSON).
   70
   71json_description(S-RDF, Key=json(JSON)) :-
   72    uri_key(S, Key, _Type),
   73    maplist(po, RDF, POList),
   74    keysort(POList, POSorted),
   75    group_pairs_by_key(POSorted, PList),
   76    properties_to_json(PList, JSON).
   77
   78po(rdf(_,P,O), P-O).
   79
   80bnode_ids([], _).
   81bnode_ids([bnode(N)|T], N) :-
   82    N2 is N + 1,
   83    bnode_ids(T, N2).
   84
   85uri_key(bnode(NodeID), Key, bnode) :-
   86    !,
   87    atom_concat('_:', NodeID, Key).
   88uri_key(BNode, _, _) :-
   89    rdf_is_bnode(BNode),
   90    !,
   91    type_error(rdf_resource, BNode).
   92uri_key(URI, URI, uri).

 graph_to_json(+Pairs:property-values, -JSON) is det

JSON is a prolog json term of grouped Pairs.

   98properties_to_json([], []) :- !.
   99properties_to_json([P-Vs|T], [P=JSON|Rest]) :-
  100    objects_to_json(Vs, JSON),
  101    properties_to_json(T, Rest).

 objects_to_json(+Objects:list(rdf_object), -JSON) is det

Convert all objects in Rs to a JSON term.

  108objects_to_json([], []) :- !.
  109objects_to_json([R|T], [json(JSON)|Vs]) :-
  110    rdf_object_to_json(R, JSON),
  111    objects_to_json(T, Vs).

 rdf_object_to_json(+RDFObject, -JSON) is det

Convert an RDF Object to a JSON term. RDFObject can be a term bnode(NodeID). RDFObject is not allowed to be a blank-node.

Errors

- type_error(rdf_resource, BNode) if RDFObject is a blank node.

  122rdf_object_to_json(literal(Lit), Object) :-
  123    !,
  124    Object = [value=Txt, type=literal|Rest],
  125    literal_to_json(Lit, Txt, Rest).
  126rdf_object_to_json(URI, [value=Key, type=Type]) :-
  127    uri_key(URI, Key, Type).

 literal_to_json(+Literal, -Text, -Attributes)

Extract text and Attributes from Literal object.

  133literal_to_json(lang(Lang, Txt), Txt, [lang=Lang]) :- !.
  134literal_to_json(type(Type, Txt), Txt, [datatype=Type]) :- !.
  135literal_to_json(Txt, Txt, [])