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    1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker and Wouter Beek
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2015-2018, VU University Amsterdam
    7                              CWI, Amsterdam
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
   19       the documentation and/or other materials provided with the
   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   26    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   28    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   29    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   30    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   32    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   33    POSSIBILITY OF SUCH DAMAGE.
   34*/
   35
   36
   37:- module(rdf11,
   38          [ rdf/3,                      % ?S, ?P, ?O
   39            rdf/4,                      % ?S, ?P, ?O, ?G
   40            rdf_has/3,                  % ?S, ?P, ?O
   41            rdf_has/4,                  % ?S, ?P, ?O, -RealP
   42            rdf_update/4,               % +S, +P, +O, +Action
   43            rdf_update/5,               % +S, +P, +O, +G, +Action
   44            rdf_reachable/3,            % ?S, ?P, ?O
   45            rdf_reachable/5,            % ?S, ?P, ?O, +MaxD, -D
   46
   47            rdf_assert/3,               % +S, +P, +O
   48            rdf_assert/4,               % +S, +P, +O, ?G
   49            rdf_retractall/3,           % ?S, ?P, ?O
   50            rdf_retractall/4,           % ?S, ?P, ?O, ?G
   51
   52            {}/1,                       % +Where
   53            rdf_where/1,                % +Where
   54            rdf_compare/3,              % -Diff, +Left, +Right
   55
   56            rdf_term/1,                 % ?Term
   57            rdf_literal/1,              % ?Term
   58            rdf_bnode/1,                % ?Term
   59            rdf_iri/1,                  % ?Term
   60            rdf_name/1,                 % ?Term
   61
   62            rdf_is_iri/1,               % @Term
   63            rdf_is_bnode/1,             % @Term
   64            rdf_is_literal/1,           % @Term
   65            rdf_is_name/1,              % @Term
   66            rdf_is_object/1,            % @Term
   67            rdf_is_predicate/1,         % @Term
   68            rdf_is_subject/1,           % @Term
   69            rdf_is_term/1,              % @Term
   70
   71            rdf_subject/1,              % ?Term
   72            rdf_predicate/1,            % ?Term
   73            rdf_object/1,               % ?Term
   74            rdf_node/1,                 % ?Term
   75
   76            rdf_create_bnode/1,         % ?Term
   77
   78            rdf_canonical_literal/2,    % +In, -Canonical
   79            rdf_lexical_form/2,         % +Literal, -Lexical
   80
   81            rdf_default_graph/1,        % -Graph
   82            rdf_default_graph/2,        % -Old, +New
   83
   84            rdf_estimate_complexity/4,  % ?S, ?P, ?O, -Estimate
   85            rdf_assert_list/2,          % +PrologList, ?RDFList
   86            rdf_assert_list/3,          % +PrologList, ?RDFList, +G
   87            rdf_last/2,                 % +RDFList, ?Last
   88            rdf_list/1,                 % ?RDFList
   89            rdf_list/2,                 % +RDFList, -PrologList
   90            rdf_length/2,               % ?RDFList, ?Length
   91            rdf_member/2,               % ?Member, +RDFList
   92            rdf_nextto/2,               % ?X, ?Y
   93            rdf_nextto/3,               % ?X, ?Y, ?RdfList
   94            rdf_nth0/3,                 % ?Index, +RDFList, ?X
   95            rdf_nth1/3,                 % ?Index, +RDFList, ?X
   96            rdf_retract_list/1,         % +RDFList
   97
   98            op(110, xfx, @),            % must be above .
   99            op(650, xfx, ^^),           % must be above :
  100            op(1150, fx, rdf_meta)
  101          ]).  102:- use_module(library(semweb/rdf_prefixes),
  103              [ (rdf_meta)/1, op(_,_,rdf_meta)
  104              ]).  105:- use_module(library(semweb/rdf_db),
  106              [ rdf_transaction/2,
  107                rdf_match_label/3,
  108                rdf_equal/2,
  109                rdf_is_bnode/1,
  110                rdf_transaction/1
  111              ]).  112
  113:- autoload(library(apply),[partition/4]).  114:- autoload(library(c14n2),[xml_write_canonical/3]).  115:- autoload(library(debug),[assertion/1,debug/3]).  116:- autoload(library(error),
  117	    [ must_be/2,
  118	      domain_error/2,
  119	      instantiation_error/1,
  120	      existence_error/2,
  121	      type_error/2,
  122	      is_of_type/2,
  123	      uninstantiation_error/1
  124	    ]).  125:- autoload(library(lists),[select/3,append/3]).  126:- autoload(library(memfile),
  127	    [new_memory_file/1,open_memory_file/3,free_memory_file/1]).  128:- autoload(library(sgml),
  129	    [ xsd_number_string/2,
  130	      xsd_time_string/3,
  131	      xml_is_dom/1,
  132	      load_xml/3,
  133	      load_html/3
  134	    ]).  135:- autoload(library(sgml_write),[html_write/3,xml_write/2]).  136:- autoload(library(solution_sequences),[distinct/2]).  137
  138:- reexport(library(semweb/rdf_db),
  139            except([ rdf/3,
  140                     rdf/4,
  141                     rdf_assert/3,
  142                     rdf_assert/4,
  143                     rdf_current_literal/1,
  144                     rdf_current_predicate/1,
  145                     rdf_has/3,
  146                     rdf_has/4,
  147                     rdf_update/4,
  148                     rdf_update/5,
  149                     rdf_reachable/3,
  150                     rdf_reachable/5,
  151                     rdf_retractall/3,
  152                     rdf_retractall/4,
  153                     rdf_node/1,
  154                     rdf_bnode/1,
  155                     rdf_is_literal/1,
  156                     rdf_is_resource/1,
  157                     rdf_literal_value/2,
  158                     rdf_compare/3,
  159                     rdf_estimate_complexity/4
  160                   ])
  161           ).

RDF 1.1 API

This library provides a new API on top of library(semweb/rdf_db). The new API follows the RDF 1.1 terminology and notation as much as possible. It runs on top of the old API, which implies that applications can use the new API in one file and the other in another one. Once the new API is considered stable and robust the old API will be deprecated.

In a nutshell, the following issues are addressed:

author
- Jan Wielemaker
- Wouter Beek
version
- 2016 */
See also
- https://github.com/SWI-Prolog/packages-semweb/wiki/Proposal-for-Semweb-library-redesign
  201:- multifile
  202    in_ground_type_hook/3,                  % +Type, +Input, -Lexical:atom
  203    out_type_hook/3,                        % +Type, -Output, +Lexical:atom
  204    invalid_lexical_form_hook/3.            % +Type, +Lexical, -Prolog
  205
  206:- meta_predicate
  207    parse_partial_xml(3,+,-).  208
  209:- rdf_meta
  210    rdf(r,r,o),
  211    rdf(r,r,o,r),
  212    rdf_assert(r,r,o),
  213    rdf_assert(r,r,o,r),
  214    rdf_has(r,r,o),
  215    rdf_has(r,r,o,-),
  216    rdf_update(r,r,o,t),
  217    rdf_update(r,r,o,r,t),
  218    rdf_reachable(r,r,o),
  219    rdf_reachable(r,r,o,+,-),
  220    rdf_retractall(r,r,o),
  221    rdf_retractall(r,r,o,r),
  222    {}(t),
  223    rdf_where(t),
  224    rdf_canonical_literal(o,-),
  225    rdf_lexical_form(o,-),
  226    rdf_compare(-,o,o),
  227    rdf_iri(r),
  228    rdf_is_iri(r),
  229    rdf_is_literal(o),
  230    rdf_is_name(o),
  231    rdf_is_object(o),
  232    rdf_is_predicate(r),
  233    rdf_is_subject(r),
  234    rdf_is_term(o),
  235    rdf_term(o),
  236    rdf_literal(o),
  237    rdf_name(o),
  238    rdf_object(o),
  239    rdf_estimate_complexity(r,r,o,-),
  240    rdf_assert_list(t,r),
  241    rdf_assert_list(t,r,r),
  242    rdf_last(r,o),
  243    rdf_list(r),
  244    rdf_list(r,-),
  245    rdf_length(r,-),
  246    rdf_member(o,r),
  247    rdf_nextto(o,o),
  248    rdf_nth0(?,r,o),
  249    rdf_nth1(?,r,o),
  250    rdf_retract_list(r).
 rdf(?S, ?P, ?O) is nondet
 rdf(?S, ?P, ?O, ?G) is nondet
True if an RDF triple <S,P,O> exists, optionally in the graph G. The object O is either a resource (atom) or one of the terms listed below. The described types apply for the case where O is unbound. If O is instantiated it is converted according to the rules described with rdf_assert/3.

Triples consist of the following three terms:

Notes:

(1) The current implementation of xsd:decimal values as floats is formally incorrect. Future versions of SWI-Prolog may introduce decimal as a subtype of rational.

(2) SS fields denote the number of seconds. This can either be an integer or a float.

(3) The date_time structure can have a 7th field that denotes the timezone offset in seconds as an integer.

In addition, a ground object value is translated into a properly typed RDF literal using rdf_canonical_literal/2.

There is a fine distinction in how duplicate statements are handled in rdf/[3,4]: backtracking over rdf/3 will never return duplicate triples that appear in multiple graphs. rdf/4 will return such duplicate triples, because their graph term differs.

Arguments:
S- is the subject term. It is either a blank node or IRI.
P- is the predicate term. It is always an IRI.
O- is the object term. It is either a literal, a blank node or IRI (except for true and false that denote the values of datatype XSD boolean).
G- is the graph term. It is always an IRI.
See also
- Triple pattern querying
- xsd_number_string/2 and xsd_time_string/3 are used to convert between lexical representations and Prolog terms.
  333rdf(S,P,O) :-
  334    pre_object(O,O0,S,P),
  335    rdf_db:rdf(S,P,O0),
  336    post_object(O,O0).
  337
  338rdf(S,P,O,G) :-
  339    pre_object(O,O0,S,P),
  340    pre_graph(G,G0),
  341    rdf_db:rdf(S,P,O0,G0),
  342    post_graph(G, G0),
  343    post_object(O,O0).
 rdf_has(?S, ?P, ?O) is nondet
 rdf_has(?S, ?P, ?O, -RealP) is nondet
Similar to rdf/3 and rdf/4, but P matches all predicates that are defined as an rdfs:subPropertyOf of P. This predicate also recognises the predicate properties inverse_of and symmetric. See rdf_set_predicate/2.
  353rdf_has(S,P,O) :-
  354    pre_object(O,O0,S,P),
  355    rdf_db:rdf_has(S,P,O0),
  356    post_object(O,O0).
  357
  358rdf_has(S,P,O,RealP) :-
  359    pre_object(O,O0,S,P),
  360    rdf_db:rdf_has(S,P,O0,RealP),
  361    post_object(O,O0).
 rdf_update(+S, +P, +O, ++Action) is det
 rdf_update(+S, +P, +O, +G, ++Action) is det
Replaces one of the three (four) fields on the matching triples depending on Action:
subject(Resource)
Changes the first field of the triple.
predicate(Resource)
Changes the second field of the triple.
object(Object)
Changes the last field of the triple to the given resource or literal(Value).
graph(Graph)
Moves the triple from its current named graph to Graph. This only works with rdf_update/5 and throws an error when used with rdf_update/4.

The argument matching Action must be ground. If this argument is equivalent to the current value, no action is performed. Otherwise, the requested action is performed on all matching triples. For example, all resources typed rdfs:Class can be changed to owl:Class using

?- rdf_update(_, rdf:type, rdfs:'Class',
              object(owl:'Class')).
Errors
- instantiation_error if Action or the matching argument is not ground.
- domain_error(rdf_update_action, Action) if Action is not one of the above terms.
  398rdf_update(S, P, O, Action) :-
  399    rdf_update(S, P, O, _, Action).
  400rdf_update(S, P, O, G, Action) :-
  401    must_be(ground, Action),
  402    (   update_column(Action, S,P,O,G, On)
  403    ->  must_be(ground, On),
  404        arg(1, Action, Old),
  405        (   On == Old
  406        ->  true
  407        ;   rdf_transaction(rdf_update_(S, P, O, G, Action), update)
  408        )
  409    ;   domain_error(rdf_update_action, Action)
  410    ).
  411
  412update_column(subject(_),   S,_,_,_, S).
  413update_column(predicate(_), _,P,_,_, P).
  414update_column(object(_),    _,_,O,_, O).
  415update_column(graph(_),     _,_,_,G, G).
  416
  417rdf_update_(S1, P, O, G, subject(S2)) :-
  418    !,
  419    forall(rdf(S1, P, O, G),
  420           ( rdf_retractall(S1, P, O, G),
  421             rdf_assert(S2, P, O, G)
  422           )).
  423rdf_update_(S, P1, O, G, predicate(P2)) :-
  424    !,
  425    forall(rdf(S, P1, O, G),
  426           ( rdf_retractall(S, P1, O, G),
  427             rdf_assert(S, P2, O, G)
  428           )).
  429rdf_update_(S, P, O1, G, object(O2)) :-
  430    !,
  431    forall(rdf(S, P, O1, G),
  432           ( rdf_retractall(S, P, O1, G),
  433             rdf_assert(S, P, O2, G)
  434           )).
  435rdf_update_(S, P, O, G1, graph(G2)) :-
  436    !,
  437    forall(rdf(S, P, O, G1),
  438           ( rdf_retractall(S, P, O, G1),
  439             rdf_assert(S, P, O, G2)
  440           )).
 rdf_reachable(?S, +P, ?O) is nondet
 rdf_reachable(?S, +P, ?O, +MaxD, -D) is nondet
True when O can be reached from S using the transitive closure of P. The predicate uses (the internals of) rdf_has/3 and thus matches both rdfs:subPropertyOf and the inverse_of and symmetric predicate properties. The version rdf_reachable/5 maximizes the steps considered and returns the number of steps taken.

If both S and O are given, these predicates are semidet. The number of steps D is minimal because the implementation uses breadth first search.

  457rdf_reachable(S,P,O) :-
  458    pre_object(O,O0,S,P),
  459    rdf_db:rdf_reachable(S,P,O0),
  460    post_object(O,O0).
  461
  462rdf_reachable(S,P,O,MaxD,D) :-
  463    pre_object(O,O0,S,P),
  464    rdf_db:rdf_reachable(S,P,O0,MaxD,D),
  465    post_object(O,O0).
 rdf_assert(+S, +P, +O) is det
 rdf_assert(+S, +P, +O, +G) is det
Assert a new triple. If O is a literal, certain Prolog terms are translated to typed RDF literals. These conversions are described with rdf_canonical_literal/2.

If a type is provided using Value^^Type syntax, additional conversions are performed. All types accept either an atom or Prolog string holding a valid RDF lexical value for the type and xsd:float and xsd:double accept a Prolog integer.

  480rdf_assert(S,P,O) :-
  481    rdf_default_graph(G),
  482    rdf_assert(S,P,O,G).
  483
  484rdf_assert(S,P,O,G) :-
  485    must_be(ground, O),
  486    pre_ground_object(O,O0),
  487    rdf_db:rdf_assert(S,P,O0,G).
 rdf_retractall(?S, ?P, ?O) is nondet
 rdf_retractall(?S, ?P, ?O, ?G) is nondet
Remove all matching triples from the database. Matching is performed using the same rules as rdf/3. The call does not instantiate any of its arguments.
  496rdf_retractall(S,P,O) :-
  497    pre_object(O,O0,S,P),
  498    rdf_db:rdf_retractall(S,P,O0).
  499
  500rdf_retractall(S,P,O,G) :-
  501    pre_object(O,O0,S,P),
  502    pre_graph(G,G0),
  503    rdf_db:rdf_retractall(S,P,O0,G0).
 rdf_compare(-Diff, +Left, +Right) is det
True if the RDF terms Left and Right are ordered according to the comparison operator Diff. The ordering is defines as:

Note that this ordering is a complete ordering of RDF terms that is consistent with the partial ordering defined by SPARQL.

Arguments:
Diff- is one of <, = or >
  524rdf_compare(Diff, Left, Right) :-
  525    pre_ground_object(Left, Left0),
  526    pre_ground_object(Right, Right0),
  527    rdf_db:rdf_compare(Diff, Left0, Right0).
 {}(+Where) is semidet
 rdf_where(+Where) is semidet
Formulate constraints on RDF terms, notably literals. These are intended to be used as illustrated below. RDF constraints are pure: they may be placed before, after or inside a graph pattern and, provided the code contains no commit operations (!, ->), the semantics of the goal remains the same. Preferably, constraints are placed before the graph pattern as they often help the RDF database to exploit its literal indexes. In the example below, the database can choose between using the subject and/or predicate hash or the ordered literal table.
    { Date >= "2000-01-01"^^xsd:date },
    rdf(S, P, Date)

The following constraints are currently defined:

>,>=,==,=<,<
The comparison operators are defined between numbers (of any recognised type), typed literals of the same type and langStrings of the same language.
prefix(String, Pattern)
substring(String, Pattern)
word(String, Pattern)
like(String, Pattern)
icase(String, Pattern)
Text matching operators that act on both typed literals and langStrings.
lang_matches(Term, Pattern)
Demands a full RDF term (Text@Lang) or a plain Lang term to match the language pattern Pattern.

The predicates rdf_where/1 and {}/1 are identical. The rdf_where/1 variant is provided to avoid ambiguity in applications where {}/1 is used for other purposes. Note that it is also possible to write rdf11:{...}.

  570{}(Where) :-
  571    rdf_where(Where).
  572
  573rdf_where(Var) :-
  574    var(Var),
  575    !,
  576    instantiation_error(Var).
  577rdf_where((A,B)) :-
  578    !,
  579    rdf_where(A),
  580    rdf_where(B).
  581rdf_where(Constraint) :-
  582    rdf_constraint(Constraint, Goal),
  583    !,
  584    call(Goal).
  585rdf_where(Constraint) :-
  586    existence_error(rdf_constraint, Constraint).
  587
  588% Comparison operators
  589rdf_constraint(Term >= Value,
  590               add_value_constraint(Term, >=, Value)).
  591rdf_constraint(Term >  Value,
  592               add_value_constraint(Term, >,  Value)).
  593rdf_constraint(Term == Value,
  594               add_value_constraint(Term, ==,  Value)).
  595rdf_constraint(Term <  Value,
  596               add_value_constraint(Term, <,  Value)).
  597rdf_constraint(Term =< Value,
  598               add_value_constraint(Term, =<, Value)).
  599% String selection
  600rdf_constraint(prefix(Term, Pattern),
  601               add_text_constraint(Term, prefix(PatternA))) :-
  602    atom_string(PatternA, Pattern).
  603rdf_constraint(substring(Term, Pattern),
  604               add_text_constraint(Term, substring(PatternA))) :-
  605    atom_string(PatternA, Pattern).
  606rdf_constraint(word(Term, Pattern),
  607               add_text_constraint(Term, word(PatternA))) :-
  608    atom_string(PatternA, Pattern).
  609rdf_constraint(like(Term, Pattern),
  610               add_text_constraint(Term, like(PatternA))) :-
  611    atom_string(PatternA, Pattern).
  612rdf_constraint(icase(Term, Pattern),
  613               add_text_constraint(Term, icase(PatternA))) :-
  614    atom_string(PatternA, Pattern).
  615% Lang selection
  616rdf_constraint(lang_matches(Term, Pattern),
  617               add_lang_constraint(Term, lang_matches(Pattern))).
  618
  619add_text_constraint(Var, Cond) :-
  620    var(Var),
  621    !,
  622    (   get_attr(Var, rdf11, Cond0)
  623    ->  put_attr(Var, rdf11, [Cond|Cond0])
  624    ;   put_attr(Var, rdf11, [Cond])
  625    ).
  626add_text_constraint(Text^^_Type, Cond) :-
  627    !,
  628    add_text_constraint(Text, Cond).
  629add_text_constraint(Text@_Lang, Cond) :-
  630    !,
  631    add_text_constraint(Text, Cond).
  632add_text_constraint(Var, Cond) :-
  633    eval_condition(Cond, Var).
 add_lang_constraint(?Term, +Constraint)
Add a constraint on the language of a literal
  639add_lang_constraint(Var, Constraint) :-
  640    var(Var),
  641    !,
  642    (   get_attr(Var, rdf11, Cond0)
  643    ->  put_attr(Var, rdf11, [Constraint|Cond0])
  644    ;   put_attr(Var, rdf11, [Constraint])
  645    ).
  646add_lang_constraint(_Text@Lang, Constraint) :-
  647    !,
  648    add_lang_constraint(Lang, Constraint).
  649add_lang_constraint(_Text^^_Type, _Constraint) :-
  650    !,
  651    fail.
  652add_lang_constraint(Term, Constraint) :-
  653    eval_condition(Constraint, Term).
 add_value_constraint(?Term, +Constraint, +Value)
Apply a value constraint to the RDF Term.
  659add_value_constraint(Term, Constraint, ValueIn) :-
  660    constraint_literal_value(ValueIn, Value),
  661    add_value_constraint_cann(Value, Constraint, Term).
  662
  663constraint_literal_value(Value, Value^^_Type) :-
  664    number(Value),
  665    !.
  666constraint_literal_value(Value, Literal) :-
  667    rdf_canonical_literal(Value, Literal).
  668
  669add_value_constraint_cann(RefVal^^Type, Constraint, Term) :-
  670    var(Term), var(Type),
  671    !,
  672    add_text_constraint(Term, value(Constraint, RefVal, Type)).
  673add_value_constraint_cann(RefVal^^Type, Constraint, Val^^Type2) :-
  674    !,
  675    Type = Type2,
  676    add_text_constraint(Val, value(Constraint, RefVal, Type)).
  677add_value_constraint_cann(RefVal@Lang, Constraint, Val@Lang) :-
  678    !,
  679    add_text_constraint(Val, value(Constraint, RefVal, lang(Lang))).
  680add_value_constraint_cann(RefVal^^Type, Constraint, Val) :-
  681    !,
  682    ground(Val),
  683    Val \= _@_,
  684    eval_condition(value(Constraint, RefVal, Type), Val).
  685
  686put_cond(Var, []) :-
  687    !,
  688    del_attr(Var, rdf11).
  689put_cond(Var, List) :-
  690    put_attr(Var, rdf11, List).
  691
  692eval_condition(Cond, Literal) :-
  693    text_condition(Cond),
  694    !,
  695    text_of(Literal, Text),
  696    text_condition(Cond, Text).
  697eval_condition(Cond, Literal) :-
  698    lang_condition(Cond),
  699    !,
  700    lang_of(Literal, Lang),
  701    lang_condition(Cond, Lang).
  702eval_condition(value(Comp, Ref, _Type), Value) :-
  703    (   number(Ref)
  704    ->  number(Value),
  705        compare_numeric(Comp, Ref, Value)
  706    ;   compare_std(Comp, Ref, Value)
  707    ).
  708
  709compare_numeric(<,  Ref, Value) :- Value  < Ref.
  710compare_numeric(=<, Ref, Value) :- Value =< Ref.
  711compare_numeric(==, Ref, Value) :- Value =:= Ref.
  712compare_numeric(>=, Ref, Value) :- Value >= Ref.
  713compare_numeric( >, Ref, Value) :- Value >  Ref.
  714
  715compare_std(<,  Ref, Value) :- Value  @< Ref.
  716compare_std(=<, Ref, Value) :- Value @=< Ref.
  717compare_std(==, Ref, Value) :- Value ==  Ref.
  718compare_std(>=, Ref, Value) :- Value @>= Ref.
  719compare_std( >, Ref, Value) :- Value @>  Ref.
  720
  721text_condition(prefix(_)).
  722text_condition(substring(_)).
  723text_condition(word(_)).
  724text_condition(like(_)).
  725text_condition(icase(_)).
  726
  727text_of(Literal, Text) :-
  728    atomic(Literal),
  729    !,
  730    Text = Literal.
  731text_of(Text@_Lang, Text).
  732text_of(Text^^_Type, Text).
  733
  734text_condition(prefix(Pattern), Text) :-
  735    rdf_match_label(prefix, Pattern, Text).
  736text_condition(substring(Pattern), Text) :-
  737    rdf_match_label(substring, Pattern, Text).
  738text_condition(word(Pattern), Text) :-
  739    rdf_match_label(word, Pattern, Text).
  740text_condition(like(Pattern), Text) :-
  741    rdf_match_label(like, Pattern, Text).
  742text_condition(icase(Pattern), Text) :-
  743    rdf_match_label(icase, Pattern, Text).
  744
  745lang_condition(lang_matches(_)).
  746
  747lang_of(_Text@Lang0, Lang) :-
  748    !,
  749    Lang = Lang0.
  750lang_of(Lang, Lang) :-
  751    atom(Lang).
  752
  753lang_condition(lang_matches(Pattern), Lang) :-
  754    rdf_db:lang_matches(Lang, Pattern).
 literal_condition(+Object, -Cond) is semidet
True when some of the constraints on Object can be translated into an equivalent query of the form literal(Cond, _Value). Translated constraints are removed from object.
  762literal_condition(Object, Cond) :-
  763    get_attr(Object, rdf11, Cond0),
  764    best_literal_cond(Cond0, Cond, Rest),
  765    put_cond(Object, Rest).
 best_literal_cond(+Conditions, -Best, -Rest) is semidet
Extract the constraints that can be translated into the Search of literal(Search, Value).
To be done
- Select the best rather than the first.
  774best_literal_cond(Conditions, Best, Rest) :-
  775    sort(Conditions, Unique),
  776    best_literal_cond2(Unique, Best, Rest).
  777
  778best_literal_cond2(Conds, Best, Rest) :-
  779    select(Cond, Conds, Rest0),
  780    rdf10_cond(Cond, Best, Rest0, Rest),
  781    !.
  782
  783rdf10_cond(value(=<, URef, UType), Cond, Rest0, Rest) :-
  784    (   select(value(>=, LRef, LType), Rest0, Rest)
  785    ->  true
  786    ;   memberchk(value(>, LRef, LType), Rest0)
  787    ->  Rest = Rest0
  788    ),
  789    !,
  790    in_constaint_type(LType, SLType, LRef, LRef0),
  791    in_constaint_type(UType, SUType, URef, URef0),
  792    Cond = between(type(SLType, LRef0), type(SUType, URef0)).
  793rdf10_cond(value(<, URef, UType), Cond, Rest0, Rest) :-
  794    (   select(value(>=, LRef, LType), Rest0, Rest1)
  795    ->  true
  796    ;   memberchk(value(>, LRef, LType), Rest0)
  797    ->  Rest1 = Rest0
  798    ),
  799    !,
  800    Rest = [value(<, URef, UType)|Rest1],
  801    in_constaint_type(LType, SLType, LRef, LRef0),
  802    in_constaint_type(UType, SUType, URef, URef0),
  803    Cond = between(type(SLType, LRef0), type(SUType, URef0)).
  804rdf10_cond(value(Cmp, Ref, Type), Pattern, Rest, Rest) :-
  805    !,
  806    rdf10_compare(Cmp, Ref, Type, Pattern).
  807rdf10_cond(lang_matches(_), _, _, _) :- !, fail.
  808rdf10_cond(Cond, Cond, Rest, Rest).
  809
  810rdf10_compare(Cmp, Ref, Type, Pattern) :-
  811    nonvar(Type), Type = lang(Lang),
  812    !,
  813    atom_string(Ref0, Ref),
  814    rdf10_lang_cond(Cmp, Ref0, Lang, Pattern).
  815rdf10_compare(Cmp, Ref, Type, Pattern) :-
  816    in_constaint_type(Type, SType, Ref, Ref0),
  817    rdf10_type_cond(Cmp, Ref0, SType, Pattern).
  818
  819rdf10_lang_cond( <, Ref, Lang, lt(lang(Lang,Ref))).
  820rdf10_lang_cond(=<, Ref, Lang, le(lang(Lang,Ref))).
  821rdf10_lang_cond(==, Ref, Lang, eq(lang(Lang,Ref))).
  822rdf10_lang_cond(>=, Ref, Lang, ge(lang(Lang,Ref))).
  823rdf10_lang_cond(>,  Ref, Lang, gt(lang(Lang,Ref))).
  824
  825rdf10_type_cond( <, Ref, Type, lt(type(Type,Ref))).
  826rdf10_type_cond(=<, Ref, Type, le(type(Type,Ref))).
  827rdf10_type_cond(==, Ref, Type, eq(type(Type,Ref))).
  828rdf10_type_cond(>=, Ref, Type, ge(type(Type,Ref))).
  829rdf10_type_cond( >, Ref, Type, gt(type(Type,Ref))).
 in_constaint_type(?Type, -SType, ++Val, -Val0)
  834in_constaint_type(Type, SType, Val, Val0) :-
  835    nonvar(Type), ground(Val),
  836    !,
  837    SType = Type,
  838    in_ground_type(Type, Val, Val0).
  839in_constaint_type(Type, SType, Val, Val0) :-
  840    var(Type), number(Val),
  841    !,
  842    (   integer(Val)
  843    ->  rdf_equal(SType, xsd:integer),
  844        in_ground_type(xsd:integer, Val, Val0)
  845    ;   float(Val)
  846    ->  rdf_equal(SType, xsd:double),
  847        in_ground_type(xsd:double, Val, Val0)
  848    ;   assertion(fail)
  849    ).
 literal_class(+Term, -Class)
Classify Term as literal and if possible as lang or typed literal on the basis of the constraints that apply to it.
  857literal_class(Term, Class) :-
  858    get_attr(Term, rdf11, Conds),
  859    select(Cond, Conds, Rest),
  860    lang_condition(Cond),
  861    !,
  862    Term = Text@Lang,
  863    put_attr(Lang, rdf11, [Cond]),
  864    put_cond(Text, Rest),
  865    (   var(Text)
  866    ->  true
  867    ;   atom_string(Text2, Text)
  868    ),
  869    Class = lang(Lang, Text2).
 attr_unify_hook(+AttributeValue, +Value)
  873attr_unify_hook(Cond, Value) :-
  874    get_attr(Value, rdf11, Cond2),
  875    !,
  876    append(Cond, Cond2, CondJ),
  877    sort(CondJ, Unique),
  878    put_cond(Value, Unique).
  879attr_unify_hook(Cond, Text^^_Type) :-
  880    var(Text),
  881    !,
  882    put_cond(Text, Cond).
  883attr_unify_hook(Cond, Text@Lang) :-
  884    var(Text), var(Lang),
  885    !,
  886    partition(lang_condition, Cond, LangCond, TextCond),
  887    put_cond(Text, TextCond),
  888    put_cond(Lang, LangCond).
  889attr_unify_hook(Cond, Value) :-
  890    sort(Cond, Unique),
  891    propagate_conditions(Unique, Value).
  892
  893propagate_conditions([], _).
  894propagate_conditions([H|T], Val) :-
  895    propagate_condition(H, Val),
  896    propagate_conditions(T, Val).
  897
  898propagate_condition(value(Comp, Ref, Type), Value) :-
  899    !,
  900    (   Value = Plain^^VType
  901    ->  VType = Type
  902    ;   Plain = Value
  903    ),
  904    cond_compare(Comp, Ref, Plain).
  905propagate_condition(lang_matches(Pattern), Value) :-
  906    !,
  907    (   Value = _@Lang
  908    ->  true
  909    ;   Lang = Value
  910    ),
  911    rdf_db:lang_matches(Lang, Pattern).
  912propagate_condition(Cond, Value) :-
  913    Cond =.. [Name|Args],
  914    Constraint =.. [Name,Value|Args],
  915    rdf_constraint(Constraint, Continuation),
  916    call(Continuation).
  917
  918cond_compare(>,  Ref, Value) :- Value @>  Ref.
  919cond_compare(>=, Ref, Value) :- Value @>= Ref.
  920cond_compare(==, Ref, Value) :- Value ==  Ref.
  921cond_compare(=<, Ref, Value) :- Value @=< Ref.
  922cond_compare( <, Ref, Value) :- Value  @< Ref.
 rdf_default_graph(-Graph) is det
 rdf_default_graph(-Old, +New) is det
Query/set the notion of the default graph. The notion of the default graph is local to a thread. Threads created inherit the default graph from their creator. See set_prolog_flag/2.
  932:- create_prolog_flag(rdf_default_graph, default,
  933                      [ type(atom),
  934                        keep(true)
  935                      ]).  936
  937rdf_default_graph(Graph) :-
  938    current_prolog_flag(rdf_default_graph, Graph).
  939rdf_default_graph(Old, New) :-
  940    current_prolog_flag(rdf_default_graph, Old),
  941    (   New == Old
  942    ->  true
  943    ;   set_prolog_flag(rdf_default_graph, New)
  944    ).
  945
  946
  947pre_graph(G, _G0) :-
  948    var(G),
  949    !.
  950pre_graph(G, G) :-
  951    atom(G),
  952    !.
  953pre_graph(G, _) :-
  954    type_error(rdf_graph, G).
  955
  956post_graph(G, G0:_) :-
  957    !,
  958    G = G0.
  959post_graph(G, G).
  960
  961
  962%   left for code calling this directly
  963
  964pre_object(Atom, URI) :-
  965    pre_object(Atom, URI, _, _).
 pre_object(+APIObject, -DBObject, +APISubject, +APIPredicate)
  969pre_object(Atom, URI, _, _) :-
  970    atom(Atom),
  971    \+ boolean(Atom),
  972    !,
  973    URI = Atom.
  974pre_object(Var, Var1, Subj, Pred) :-
  975    var(Var),
  976    !,
  977    (   literal_condition(Var, Cond)
  978    ->  Var1 = literal(Cond, _)
  979    ;   literal_class(Var, Value)
  980    ->  Var1 = literal(Value)
  981    ;   (   Var == Subj
  982        ->  Var1 = Subj
  983        ;   true
  984        ),
  985        (   Var == Pred
  986        ->  Var1 = Pred
  987        ;   true
  988        )
  989    ).
  990pre_object(Val@Lang, Var1, _, _) :-
  991    !,
  992    (   literal_condition(Val, Cond)
  993    ->  Var1 = literal(Cond, lang(Lang, _))
  994    ;   literal_class(Val@Lang, Class)
  995    ->  Var1 = literal(Class)
  996    ;   in_lang_string(Val, Val0),
  997        Var1 = literal(lang(Lang, Val0))
  998    ).
  999pre_object(Val^^Type, Var1, _, _) :-
 1000    !,
 1001    (   literal_condition(Val, Cond)
 1002    ->  Var1 = literal(Cond, type(Type, _))
 1003    ;   in_type(Type, Val, Type0, Val0),
 1004        (   var(Type0), var(Val0)
 1005        ->  Var1 = literal(_)
 1006        ;   Var1 = literal(type(Type0, Val0))
 1007        )
 1008    ).
 1009pre_object(Obj, Val0, _, _) :-
 1010    ground(Obj),
 1011    !,
 1012    pre_ground_object(Obj, Val0).
 1013pre_object(Obj, _, _, _) :-
 1014    type_error(rdf_object, Obj).
 pre_ground_object(+Object, -RDF) is det
Convert between a Prolog value and an RDF value for rdf_assert/3 and friends. Auto-conversion:
 1057:- rdf_meta
 1058    pre_ground_object(+, o). 1059
 1060% Interpret Prolog integer as xsd:integer.
 1061pre_ground_object(Int, Object) :-
 1062    integer(Int),
 1063    !,
 1064    rdf_equal(Object, literal(type(xsd:integer, Atom))),
 1065    atom_number(Atom, Int).
 1066% Interpret Prolog floating-point value as xsd:double.
 1067pre_ground_object(Float, Object) :-
 1068    float(Float),
 1069    !,
 1070    rdf_equal(Object, literal(type(xsd:double, Atom))),
 1071    xsd_number_string(Float, String),
 1072    atom_string(Atom, String).
 1073% Interpret SWI string as xsd:string.
 1074pre_ground_object(String, Object) :-
 1075    string(String),
 1076    !,
 1077    rdf_equal(Object, literal(type(xsd:string, Atom))),
 1078    atom_string(Atom, String).
 1079% Interpret `false' and `true' as the Boolean values.
 1080pre_ground_object(false, literal(type(xsd:boolean, false))) :- !.
 1081pre_ground_object(true, literal(type(xsd:boolean, true))) :- !.
 1082% Interpret date(Y,M,D) as xsd:date,
 1083%           date_time(Y,M,D,HH,MM,SS) as xsd:dateTime,
 1084%           date_time(Y,M,D,HH,MM,SS,TZ) as xsd:dateTime,
 1085%           month_day(M,D) as xsd:gMonthDay,
 1086%           year_month(Y,M) as xsd:gYearMonth, and
 1087%           time(HH,MM,SS) as xsd:time.
 1088pre_ground_object(Term, literal(type(Type, Atom))) :-
 1089    xsd_date_time_term(Term),
 1090    !,
 1091    xsd_time_string(Term, Type, String),
 1092    atom_string(Atom, String).
 1093pre_ground_object(Val@Lang,  literal(lang(Lang0, Val0))) :-
 1094    !,
 1095    downcase_atom(Lang, Lang0),
 1096    in_lang_string(Val, Val0).
 1097pre_ground_object(Val^^Type, literal(type(Type0, Val0))) :-
 1098    !,
 1099    in_type(Type, Val, Type0, Val0).
 1100pre_ground_object(Atom, URI) :-
 1101    atom(Atom),
 1102    !,
 1103    URI = Atom.
 1104pre_ground_object(literal(Lit0), literal(Lit)) :-
 1105    old_literal(Lit0, Lit),
 1106    !.
 1107pre_ground_object(Value, _) :-
 1108    type_error(rdf_object, Value).
 1109
 1110xsd_date_time_term(date(_,_,_)).
 1111xsd_date_time_term(date_time(_,_,_,_,_,_)).
 1112xsd_date_time_term(date_time(_,_,_,_,_,_,_)).
 1113xsd_date_time_term(month_day(_,_)).
 1114xsd_date_time_term(year_month(_,_)).
 1115xsd_date_time_term(time(_,_,_)).
 1116
 1117old_literal(Lit0, Lit) :-
 1118    old_literal(Lit0),
 1119    !,
 1120    Lit = Lit0.
 1121old_literal(Atom, Lit) :-
 1122    atom(Atom),
 1123    rdf_equal(xsd:string, XSDString),
 1124    Lit = type(XSDString, Atom).
 1125
 1126old_literal(type(Type, Value)) :-
 1127    atom(Type), atom(Value).
 1128old_literal(lang(Lang, Value)) :-
 1129    atom(Lang), atom(Value).
 1130
 1131in_lang_string(Val, Val0) :-
 1132    atomic(Val),
 1133    !,
 1134    atom_string(Val0, Val).
 1135in_lang_string(_, _).
 1136
 1137in_type(Type, Val, Type, Val0) :-
 1138    nonvar(Type), ground(Val),
 1139    !,
 1140    in_ground_type(Type, Val, Val0).
 1141in_type(VarType, Val, VarType, Val0) :-
 1142    ground(Val),
 1143    \+ catch(xsd_number_string(_, Val), _, fail),
 1144    !,
 1145    atom_string(Val0, Val).
 1146in_type(_, _, _, _).
 1147
 1148:- rdf_meta
 1149    in_ground_type(r,?,?),
 1150    in_date_component(r, +, +, -).
 in_ground_type(+Type, +Input, -Lexical:atom) is det
Translate the Prolog date Input according to Type into its RDF lexical form. The lecical form is represented as an atom. In future versions this is likely to become a string.
 1158in_ground_type(Type, Input, Lex) :-
 1159    \+ string(Input),
 1160    in_ground_type_hook(Type, Input, Lex),
 1161    !.
 1162in_ground_type(IntType, Val, Val0) :-
 1163    xsd_numerical(IntType, Domain, PrologType),
 1164    !,
 1165    in_number(PrologType, Domain, IntType, Val, Val0).
 1166in_ground_type(xsd:boolean, Val, Val0) :-
 1167    !,
 1168    (   in_boolean(Val, Val0)
 1169    ->  true
 1170    ;   type_error(rdf_boolean, Val)
 1171    ).
 1172in_ground_type(rdf:langString, _Val0, _) :-
 1173    !,
 1174    domain_error(rdf_data_type, rdf:langString).
 1175in_ground_type(DateTimeType, Val, Val0) :-
 1176    xsd_date_time_type(DateTimeType),
 1177    !,
 1178    in_date_time(DateTimeType, Val, Val0).
 1179in_ground_type(rdf:'XMLLiteral', Val, Val0) :-
 1180    !,
 1181    in_xml_literal(xml, Val, Val0).
 1182in_ground_type(rdf:'HTML', Val, Val0) :-
 1183    !,
 1184    in_xml_literal(html, Val, Val0).
 1185in_ground_type(_Unknown, Val, Val0) :-
 1186    atom_string(Val0, Val).
 in_date_time(+Type, +Input, -Lexical) is det
Accepts either a term as accepted by xsd_time_string/3 or a valid string for the corresponding XSD type.
 1193:- rdf_meta
 1194    in_date_time(r,+,-). 1195
 1196in_date_time(Type, Text, Text0) :-
 1197    atom(Text),
 1198    !,
 1199    xsd_time_string(_, Type, Text),
 1200    Text0 = Text.
 1201in_date_time(Type, Text, Text0) :-
 1202    string(Text),
 1203    !,
 1204    xsd_time_string(_, Type, Text),
 1205    atom_string(Text0, Text).
 1206in_date_time(xsd:dateTime, Stamp, Text0) :-
 1207    number(Stamp),
 1208    !,
 1209    format_time(atom(Text0), '%FT%T%:z', Stamp).
 1210in_date_time(Type, Term, Text0) :-
 1211    !,
 1212    xsd_time_string(Term, Type, String),
 1213    atom_string(Text0, String).
 in_boolean(?NonCanonical, ?Canonical)
True when Canonical is the canonical boolean for NonCanonical.
 1220in_boolean(true,    true).
 1221in_boolean(false,   false).
 1222in_boolean("true",  true).
 1223in_boolean("false", false).
 1224in_boolean(1,       true).
 1225in_boolean(0,       false).
 1226
 1227boolean(false).
 1228boolean(true).
 in_number(+PrologType, +Domain, +XSDType, +Value, -Lexical)
Lexical is the lexical representation for Value.
Errors
- type_error(PrologType, Value)
- domain_error(XSDType, Value)
 1237in_number(integer, Domain, XSDType, Val, Val0) :-
 1238    integer(Val),
 1239    !,
 1240    check_integer_domain(Domain, XSDType, Val),
 1241    atom_number(Val0, Val).
 1242in_number(integer, Domain, XSDType, Val, Val0) :-
 1243    atomic(Val),
 1244    atom_number(Val, Num),
 1245    integer(Num),
 1246    !,
 1247    check_integer_domain(Domain, XSDType, Num),
 1248    atom_number(Val0, Num).
 1249in_number(double, _Domain, _, Val, Val0) :-
 1250    number(Val),
 1251    !,
 1252    ValF is float(Val),
 1253    xsd_number_string(ValF, ValS),
 1254    atom_string(Val0, ValS).
 1255in_number(double, _Domain, _, Val, Val0) :-
 1256    atomic(Val),
 1257    xsd_number_string(Num, Val),
 1258    ValF is float(Num),
 1259    !,
 1260    xsd_number_string(ValF, ValS),
 1261    atom_string(Val0, ValS).
 1262in_number(PrologType, _, _, Val, _) :-
 1263    type_error(PrologType, Val).
 1264
 1265check_integer_domain(PLType, _, Val) :-
 1266    is_of_type(PLType, Val),
 1267    !.
 1268check_integer_domain(_, XSDType, Val) :-
 1269    domain_error(XSDType, Val).
 1270
 1271error:has_type(nonpos, T):-
 1272    integer(T),
 1273    T =< 0.
 1274
 1275%check_integer_domain(between(Low, High), XSDType, Val) :-
 1276%       (   between(Low, High, Val)
 1277%       ->  true
 1278%       ;   domain_error(XSDType, Val)
 1279%       ).
 1280%check_integer_domain(integer, _, _).
 xsd_numerical(?URI, ?TypeCheck, ?PrologType)
 1284:- rdf_meta
 1285    xsd_numerical(r, ?, ?). 1286
 1287xsd_numerical(xsd:byte,               between(-128,127),               integer).
 1288xsd_numerical(xsd:double,             float,                           double).
 1289xsd_numerical(xsd:decimal,            float,                           double).
 1290xsd_numerical(xsd:float,              float,                           double).
 1291xsd_numerical(xsd:int,                between(-2147483648,2147483647), integer).
 1292xsd_numerical(xsd:integer,            integer,                         integer).
 1293xsd_numerical(xsd:long,               between(-9223372036854775808,
 1294                                               9223372036854775807),   integer).
 1295xsd_numerical(xsd:negativeInteger,    negative_integer,                integer).
 1296xsd_numerical(xsd:nonNegativeInteger, nonneg,                          integer).
 1297xsd_numerical(xsd:nonPositiveInteger, nonpos,                          integer).
 1298xsd_numerical(xsd:positiveInteger,    positive_integer,                integer).
 1299xsd_numerical(xsd:short,              between(-32768,32767),           integer).
 1300xsd_numerical(xsd:unsignedByte,       between(0,255),                  integer).
 1301xsd_numerical(xsd:unsignedInt,        between(0,4294967295),           integer).
 1302xsd_numerical(xsd:unsignedLong,       between(0,18446744073709551615), integer).
 1303xsd_numerical(xsd:unsignedShort,      between(0,65535),                integer).
 xsd_date_time_type(?URI)
True when URI is an XSD date or time type.
 1309:- rdf_meta
 1310    xsd_date_time_type(r). 1311
 1312xsd_date_time_type(xsd:date).
 1313xsd_date_time_type(xsd:dateTime).
 1314xsd_date_time_type(xsd:gDay).
 1315xsd_date_time_type(xsd:gMonth).
 1316xsd_date_time_type(xsd:gMonthDay).
 1317xsd_date_time_type(xsd:gYear).
 1318xsd_date_time_type(xsd:gYearMonth).
 1319xsd_date_time_type(xsd:time).
 in_xml_literal(+Type, +Val, -Val0) is det
Translate an XMLLiteral or HTML literal to its canonical textual representation. Input is either text or a Prolog XML DOM.
To be done
- Deal with partial content?
 1329in_xml_literal(Type, Val, Val0) :-
 1330    xml_is_dom(Val),
 1331    !,
 1332    write_xml_literal(Type, Val, Val0).
 1333in_xml_literal(xml, Val, Val0) :-
 1334    parse_partial_xml(load_xml, Val, DOM),
 1335    write_xml_literal(xml, DOM, Val0).
 1336in_xml_literal(html, Val, Val0) :-
 1337    parse_partial_xml(load_html, Val, DOM),
 1338    write_xml_literal(html, DOM, Val0).
 1339
 1340parse_partial_xml(Parser, Val, DOM) :-
 1341    setup_call_cleanup(
 1342        new_memory_file(MF),
 1343        (   setup_call_cleanup(
 1344                open_memory_file(MF, write, Out),
 1345                format(Out, "<xml>~w</xml>", [Val]),
 1346                close(Out)),
 1347            setup_call_cleanup(
 1348                open_memory_file(MF, read, In),
 1349                call(Parser, stream(In), [element(xml, _, DOM)], []),
 1350                close(In))
 1351        ),
 1352        free_memory_file(MF)).
 1353
 1354
 1355write_xml_literal(xml, DOM, Text) :-
 1356    with_output_to(atom(Text),
 1357                   xml_write_canonical(current_output, DOM, [])).
 1358write_xml_literal(html, DOM, Text) :-
 1359    with_output_to(atom(Text),
 1360                   html_write(current_output, DOM,
 1361                              [ header(false),
 1362                                layout(false)
 1363                              ])).
 rdf_canonical_literal(++In, -Literal) is det
Transform a relaxed literal specification as allowed for rdf_assert/3 into its canonical form. The following Prolog terms are translated:
Prolog TermDatatype IRI
floatxsd:double
integerxsd:integer
stringxsd:string
true or falsexsd:boolean
date(Y,M,D)xsd:date
date_time(Y,M,D,HH,MM,SS)xsd:dateTime
date_time(Y,M,D,HH,MM,SS,TZ)xsd:dateTime
month_day(M,D)xsd:gMonthDay
year_month(Y,M)xsd:gYearMonth
time(HH,MM,SS)xsd:time

For example:

?- rdf_canonical_literal(42, X).
X = 42^^'http://www.w3.org/2001/XMLSchema#integer'.
 1391rdf_canonical_literal(In, Literal) :-
 1392    ground(In),
 1393    !,
 1394    pre_ground_object(In, DBTerm),
 1395    post_object(Literal, DBTerm).
 1396rdf_canonical_literal(In, _) :-
 1397    must_be(ground, In).
 rdf_lexical_form(++Literal, -Lexical:compound) is det
True when Lexical is the lexical form for the literal Literal. Lexical is of one of the forms below. The ntriples serialization is obtained by transforming String into a proper ntriples string using double quotes and escaping where needed and turning Type into a proper IRI reference.
 1410%       For example,
 1411%
 1412%       ==
 1413%       ?- rdf_lexical_form(2.3^^xsd:double, L).
 1414%       L = "2.3E0"^^'http://www.w3.org/2001/XMLSchema#double'.
 1415%       ==
 1416
 1417rdf_lexical_form(Literal, Lexical) :-
 1418    pre_ground_object(Literal, literal(Lit0)),
 1419    !,
 1420    text_of0(Lit0, Lexical).
 1421rdf_lexical_form(Literal, _) :-
 1422    type_error(rdf_literal, Literal).
 1423
 1424text_of0(type(TypeA, LexicalA), LexicalS^^TypeA) :-
 1425    atom_string(LexicalA, LexicalS).
 1426text_of0(lang(LangA, LexicalA), LexicalS@LangA) :-
 1427    atom_string(LexicalA, LexicalS).
 1428
 1429
 1430                 /*******************************
 1431                 *       POST PROCESSING        *
 1432                 *******************************/
 1433
 1434:- rdf_meta
 1435    post_object(o,o),
 1436    out_type(r,-,+). 1437
 1438post_object(Val, _) :-
 1439    ground(Val),
 1440    !.                 % already specified and matched
 1441post_object(URI, URI0) :-
 1442    atom(URI0),
 1443    !,
 1444    URI = URI0.
 1445post_object(Val@Lang, literal(lang(Lang, Val0))) :-
 1446    nonvar(Lang),          % lang(Lang,Text) returns var(Lang) if no lang
 1447    !,
 1448    atom_string(Val0, Val).
 1449post_object(Val^^Type, literal(type(Type, Val0))) :-
 1450    !,
 1451    out_type(Type, Val, Val0).
 1452post_object(Val^^xsd:string, literal(Plain)) :-
 1453    !,
 1454    atomic(Plain),
 1455    atom_string(Plain, Val).
 1456post_object(Val@Lang, literal(_, lang(Lang, Val0))) :-
 1457    nonvar(Lang),
 1458    !,
 1459    atom_string(Val0, Val).
 1460post_object(Val^^Type, literal(_, type(Type, Val0))) :-
 1461    !,
 1462    out_type(Type, Val, Val0).
 1463post_object(Val^^xsd:string, literal(_, Plain)) :-
 1464    atomic(Plain),
 1465    atom_string(Plain, Val).
 1466
 1467out_type(xsd:string, Val, Val0) :-     % catches unbound type too
 1468    !,
 1469    atom_string(Val0, Val).
 1470out_type(Type, Val, Val0) :-
 1471    out_type_hook(Type, Val, Val0),
 1472    !.
 1473out_type(IntType, Val, Val0) :-
 1474    xsd_numerical(IntType, _Domain, _BasicType),
 1475    !,
 1476    xsd_number_string(Val, Val0).
 1477out_type(DateTimeType, Val, Val0) :-
 1478    xsd_date_time_type(DateTimeType),
 1479    !,
 1480    out_date_time(DateTimeType, Val, Val0).
 1481out_type(xsd:boolean, Val, Val0) :-
 1482    !,
 1483    Val = Val0.
 1484out_type(rdf:'XMLLiteral', XML, DOM) :-
 1485    xml_is_dom(DOM),
 1486    !,
 1487    with_output_to(string(XML),
 1488                   xml_write(DOM, [header(false)])).
 1489out_type(_Unknown, Val, Val0) :-
 1490    atom_string(Val0, Val).
 out_date_time(+DateTimeType, -Val, +Val0) is det
Translate an XSD lexical form for a date/time related datatype into the cannical form as defined by xsd_time_string/3.
 1498out_date_time(Type, Prolog, Lexical) :-
 1499    catch(xsd_time_string(Prolog, Type, Lexical),
 1500          error(_,_),
 1501          invalid_lexical_form_hook(Type, Lexical, Prolog)).
 invalid_lexical_form_hook(+Type, +Lexical, -Prolog)
This hook is called if translation of the lexical form to the Prolog representation fails due to a syntax error. By default it is not defined, causing such invalid triples to be silently ignored.
 1511                 /*******************************
 1512                 *          ENUMERATION         *
 1513                 *******************************/
 rdf_term(?Term) is nondet
True if Term appears in the RDF database. Term is either an IRI, literal or blank node and may appear in any position of any triple. If Term is ground, it is pre-processed as the object argument of rdf_assert/3 and the predicate is semidet.
 1522rdf_term(N) :-
 1523    ground(N),
 1524    !,
 1525    pre_object(N, N0, _, _),
 1526    visible_term(N0).
 1527rdf_term(N) :-
 1528    gen_term(N).
 1529
 1530gen_term(N) :-
 1531    resource(N),
 1532    visible_term(N).
 1533gen_term(O) :-                          % performs double conversion!
 1534    rdf_literal(O),
 1535    (rdf(_,_,O) -> true).
 rdf_literal(?Term) is nondet
True if Term is a known literal. If Term is ground, it is pre-processed as the object argument of rdf_assert/3 and the predicate is semidet.
 1543rdf_literal(Term) :-
 1544    ground(Term),
 1545    !,
 1546    pre_ground_object(Term, Object),
 1547    (rdf_db:rdf(_,_,Object)->true).
 1548rdf_literal(Term) :-
 1549    pre_object(Term,literal(Lit0), _, _),
 1550    rdf_db:rdf_current_literal(Lit0),
 1551    (rdf_db:rdf(_,_,literal(Lit0))->true),
 1552    post_object(Term, literal(Lit0)).
 rdf_bnode(?BNode) is nondet
True if BNode is a currently known blank node. The predicate is semidet if BNode is ground.
 1559rdf_bnode(BNode) :-
 1560    atom(BNode),
 1561    !,
 1562    current_bnode(BNode).
 1563rdf_bnode(BNode) :-
 1564    rdf_db:rdf_resource(BNode),
 1565    current_bnode(BNode).
 1566
 1567current_bnode(BNode) :-
 1568    rdf_is_bnode(BNode),
 1569    visible_node(BNode).            % Assumes BNodes cannot be predicates
 rdf_iri(?IRI) is nondet
True if IRI is a current IRI. The predicate is semidet if IRI is ground.
 1576rdf_iri(IRI) :-
 1577    atom(IRI),
 1578    !,
 1579    \+ rdf_is_bnode(IRI),
 1580    visible_term(IRI).
 1581rdf_iri(IRI) :-
 1582    resource(IRI),
 1583    \+ rdf_is_bnode(IRI),
 1584    visible_term(IRI).
 rdf_name(?Name) is nondet
True if Name is a current IRI or literal. The predicate is semidet if Name is ground.
 1591rdf_name(Name) :-
 1592    atom(Name), \+ boolean(Name),
 1593    !,
 1594    \+ rdf_is_bnode(Name),
 1595    visible_term(Name).
 1596rdf_name(Name) :-
 1597    ground(Name),
 1598    !,
 1599    pre_ground_object(Name, Name0),
 1600    (rdf_db:rdf(_,_,Name0)->true).
 1601rdf_name(Name) :-
 1602    rdf_iri(Name).
 1603rdf_name(Name) :-
 1604    rdf_literal(Name).
 rdf_subject(?S) is nondet
True when S is a currently known subject, i.e. it appears in the subject position of some visible triple. The predicate is semidet if S is ground.
 rdf_predicate(?P) is nondet
True when P is a currently known predicate, i.e. it appears in the predicate position of some visible triple. The predicate is semidet if P is ground.
 1619rdf_predicate(P) :-
 1620    atom(P),
 1621    !,
 1622    (rdf(_,P,_) -> true).
 1623rdf_predicate(P) :-
 1624    rdf_db:rdf_current_predicate(P),
 1625    (rdf(_,P,_) -> true).
 rdf_object(?O) is nondet
True when O is a currently known object, i.e. it appears in the object position of some visible triple. If Term is ground, it is pre-processed as the object argument of rdf_assert/3 and the predicate is semidet.
 1634rdf_object(O) :-
 1635    ground(O),
 1636    !,
 1637    (   atom(O), \+ boolean(O)
 1638    ->  (rdf_db:rdf(_,_,O) -> true)
 1639    ;   rdf_literal(O)
 1640    ).
 1641rdf_object(O) :-
 1642    rdf_db:rdf_resource(O),
 1643    (rdf_db:rdf(_,_,O) -> true).
 1644rdf_object(O) :-
 1645    rdf_literal(O).
 rdf_node(?T) is nondet
True when T appears in the subject or object position of a known triple, i.e., is a node in the RDF graph.
 1652rdf_node(N) :-
 1653    var(N),
 1654    !,
 1655    gen_node(N).
 1656rdf_node(N) :-
 1657    pre_ground_object(N, N0),
 1658    visible_node(N0).
 1659
 1660gen_node(N) :-
 1661    rdf_db:rdf_resource(N),
 1662    visible_node(N).
 1663gen_node(O) :-                          % performs double conversion!
 1664    rdf_literal(O),
 1665    (rdf(_,_,O) -> true).
 resource(?R)
True if R is a node that is not a literal. Note that RDF-DB does not necessarily include predicates in the set of resources. Also note that the resource may not really exist or be visible.
 1673resource(R) :-
 1674    var(R),
 1675    !,
 1676    gen_resource(R).
 1677resource(R) :-
 1678    rdf_db:rdf_resource(R),
 1679    !.
 1680resource(R) :-
 1681    rdf_db:rdf_current_predicate(R),
 1682    !.
 1683
 1684gen_resource(R) :-
 1685    rdf_db:rdf_resource(R).
 1686gen_resource(R) :-
 1687    rdf_db:rdf_current_predicate(R),
 1688    \+ rdf_db:rdf_resource(R).
 1689
 1690visible_node(Term) :-
 1691    atom(Term),
 1692    !,
 1693    (   rdf_db:rdf(Term,_,_)
 1694    ;   rdf_db:rdf(_,_,Term)
 1695    ),
 1696    !.
 1697visible_node(Term) :-
 1698    rdf_db:rdf(_,_,Term).
 1699
 1700visible_term(Term) :-
 1701    atom(Term),
 1702    !,
 1703    (   rdf_db:rdf(Term,_,_)
 1704    ;   rdf_db:rdf(_,Term,_)
 1705    ;   rdf_db:rdf(_,_,Term)
 1706    ),
 1707    !.
 1708visible_term(Term) :-
 1709    rdf_db:rdf(_,_,Term).
 rdf_create_bnode(--BNode)
Create a new BNode. A blank node is an atom starting with _:. Blank nodes generated by this predicate are of the form _:genid followed by a unique integer.
 1717rdf_create_bnode(BNode) :-
 1718    var(BNode),
 1719    !,
 1720    rdf_db:rdf_bnode(BNode).
 1721rdf_create_bnode(BNode) :-
 1722    uninstantiation_error(BNode).
 1723
 1724
 1725                 /*******************************
 1726                 *         TYPE CHECKING        *
 1727                 *******************************/
 rdf_is_iri(@IRI) is semidet
True if IRI is an RDF IRI term.

For performance reasons, this does not check for compliance to the syntax defined in RFC 3987. This checks whether the term is (1) an atom and (2) not a blank node identifier.

Success of this goal does not imply that the IRI is present in the database (see rdf_iri/1 for that).

 1742rdf_is_iri(IRI) :-
 1743    atom(IRI),
 1744    \+ rdf_is_bnode(IRI).
 rdf_is_bnode(@Term) is semidet
True if Term is an RDF blank node identifier.

A blank node is represented by an atom that starts with _:.

Success of this goal does not imply that the blank node is present in the database (see rdf_bnode/1 for that).

For backwards compatibility, atoms that are represented with an atom that starts with __ are also considered to be a blank node.

 rdf_is_literal(@Term) is semidet
True if Term is an RDF literal term.

An RDF literal term is of the form `String@LanguageTag or Value^^Datatype`.

Success of this goal does not imply that the literal is well-formed or that it is present in the database (see rdf_literal/1 for that).

 1772rdf_is_literal(Literal) :-
 1773    literal_form(Literal),
 1774    !,
 1775    ground(Literal).
 1776
 1777literal_form(_@_).
 1778literal_form(_^^_).
 rdf_is_name(@Term) is semidet
True if Term is an RDF Name, i.e., an IRI or literal.

Success of this goal does not imply that the name is well-formed or that it is present in the database (see rdf_name/1 for that).

 1789rdf_is_name(T) :- rdf_is_iri(T), !.
 1790rdf_is_name(T) :- rdf_is_literal(T).
 rdf_is_object(@Term) is semidet
True if Term can appear in the object position of a triple.

Success of this goal does not imply that the object term in well-formed or that it is present in the database (see rdf_object/1 for that).

Since any RDF term can appear in the object position, this is equaivalent to rdf_is_term/1.

 1804rdf_is_object(T) :- rdf_is_subject(T), !.
 1805rdf_is_object(T) :- rdf_is_literal(T).
 rdf_is_predicate(@Term) is semidet
True if Term can appear in the predicate position of a triple.

Success of this goal does not imply that the predicate term is present in the database (see rdf_predicate/1 for that).

Since only IRIs can appear in the predicate position, this is equivalent to rdf_is_iri/1.

 1818rdf_is_predicate(T) :- rdf_is_iri(T).
 rdf_is_subject(@Term) is semidet
True if Term can appear in the subject position of a triple.

Only blank nodes and IRIs can appear in the subject position.

Success of this goal does not imply that the subject term is present in the database (see rdf_subject/1 for that).

Since blank nodes are represented by atoms that start with `_:` and an IRIs are atoms as well, this is equivalent to atom(Term).

 1834rdf_is_subject(T) :- atom(T).
 rdf_is_term(@Term) is semidet
True if Term can be used as an RDF term, i.e., if Term is either an IRI, a blank node or an RDF literal.

Success of this goal does not imply that the RDF term is present in the database (see rdf_term/1 for that).

 1844rdf_is_term(N) :- rdf_is_subject(N), !.
 1845rdf_is_term(N) :- rdf_is_literal(N).
 1846
 1847
 1848                 /*******************************
 1849                 *          COLLECTIONS         *
 1850                 *******************************/
 rdf_list(?RDFTerm) is semidet
True if RDFTerm is a proper RDF list. This implies that every node in the list has an rdf:first and rdf:rest property and the list ends in rdf:nil.

If RDFTerm is unbound, RDFTerm is bound to each maximal RDF list. An RDF list is maximal if there is no triple rdf(_, rdf:rest, RDFList).

 1862rdf_list(L) :-
 1863    var(L),
 1864    !,
 1865    rdf_has(L, rdf:first, _),
 1866    \+ rdf_has(_, rdf:rest, L),
 1867    rdf_list_g(L).
 1868rdf_list(L) :-
 1869    rdf_list_g(L),
 1870    !.
 1871
 1872:- rdf_meta
 1873    rdf_list_g(r). 1874
 1875rdf_list_g(rdf:nil) :- !.
 1876rdf_list_g(L) :-
 1877    once(rdf_has(L, rdf:first, _)),
 1878    rdf_has(L, rdf:rest, Rest),
 1879    (   rdf_equal(rdf:nil, Rest)
 1880    ->  true
 1881    ;   rdf_list_g(Rest)
 1882    ).
 rdf_list(+RDFList, -PrologList) is det
True when PrologList represents the rdf:first objects for all cells in RDFList. Note that this can be non-deterministic if cells have multiple rdf:first or rdf:rest triples.
 1891rdf_list(RDFList, Prolog) :-
 1892    rdf_is_subject(RDFList),
 1893    !,
 1894    rdf_list_to_prolog(RDFList, Prolog).
 1895rdf_list(RDFList, _Prolog) :-
 1896    type_error(rdf_subject, RDFList).
 1897
 1898:- rdf_meta
 1899    rdf_list_to_prolog(r,-). 1900
 1901rdf_list_to_prolog(rdf:nil, Prolog) :-
 1902    !,
 1903    Prolog = [].
 1904rdf_list_to_prolog(RDF, [H|T2]) :-
 1905    (   rdf_has(RDF, rdf:first, H0),
 1906        rdf_has(RDF, rdf:rest, T1)
 1907    *-> H = H0,
 1908        rdf_list_to_prolog(T1, T2)
 1909    ;   type_error(rdf_list, RDF)
 1910    ).
 rdf_length(+RDFList, -Length:nonneg) is nondet
True when Length is the number of cells in RDFList. Note that a list cell may have multiple rdf:rest triples, which makes this predicate non-deterministic. This predicate does not check whether the list cells have associated values (rdf:first). The list must end in rdf:nil.
 1921rdf_length(RDFList, Len) :-
 1922    rdf_is_subject(RDFList),
 1923    !,
 1924    rdf_length(RDFList, 0, Len).
 1925
 1926:- rdf_meta
 1927    rdf_length(r,+,-). 1928
 1929rdf_length(rdf:nil, Len, Len) :- !.
 1930rdf_length(RDF, Len0, Len) :-
 1931    (   rdf_has(RDF, rdf:rest, T)
 1932    *-> Len1 is Len0+1,
 1933        rdf_length(T, Len1, Len)
 1934    ;   type_error(rdf_list, RDF)
 1935    ).
 rdf_member(?Member, +RDFList) is nondet
True when Member is a member of RDFList
 1942rdf_member(M, L) :-
 1943    ground(M),
 1944    !,
 1945    (   rdf_member2(M, L)
 1946    ->  true
 1947    ).
 1948rdf_member(M, L) :-
 1949    rdf_member2(M, L).
 1950
 1951rdf_member2(M, L) :-
 1952    rdf_has(L, rdf:first, M).
 1953rdf_member2(M, L) :-
 1954    rdf_has(L, rdf:rest, L1),
 1955    rdf_member2(M, L1).
 rdf_nextto(?X, ?Y) is nondet
 rdf_nextto(?X, ?Y, ?RdfList) is nondet
True if Y directly follows X in RdfList.
 1963rdf_nextto(X, Y) :-
 1964    distinct(X-Y, rdf_nextto(X, Y, _)).
 1965
 1966
 1967rdf_nextto(X, Y, L) :-
 1968    var(X), ground(Y),
 1969    !,
 1970    rdf_nextto(Y, X, L).
 1971rdf_nextto(X, Y, L) :-
 1972    rdf_has(L, rdf:first, X),
 1973    rdf_has(L, rdf:rest, T),
 1974    rdf_has(T, rdf:first, Y).
 rdf_nth0(?Index, +RDFList, ?X) is nondet
 rdf_nth1(?Index, +RDFList, ?X) is nondet
True when X is the Index-th element (0-based or 1-based) of RDFList. This predicate is deterministic if Index is given and the list has no multiple rdf:first or rdf:rest values.
 1984rdf_nth0(I, L, X) :-
 1985    rdf_nth(0, I, L, X).
 1986
 1987rdf_nth1(I, L, X) :-
 1988    rdf_nth(1, I, L, X).
 1989
 1990rdf_nth(Offset, I, L, X) :-
 1991    rdf_is_subject(L),
 1992    !,
 1993    (   var(I)
 1994    ->  true
 1995    ;   must_be(nonneg, I)
 1996    ),
 1997    rdf_nth_(I, Offset, L, X).
 1998rdf_nth(_, _, L, _) :-
 1999    type_error(rdf_subject, L).
 2000
 2001rdf_nth_(I, I0, L, X) :-
 2002    (   I0 == I
 2003    ->  !
 2004    ;   I0 = I
 2005    ),
 2006    rdf_has(L, rdf:first, X).
 2007rdf_nth_(I, I0, L, X) :-
 2008    rdf_has(L, rdf:rest, T),
 2009    I1 is I0+1,
 2010rdf_nth_(I, I1, T, X).
 rdf_last(+RDFList, -Last) is det
True when Last is the last element of RDFList. Note that if the last cell has multiple rdf:first triples, this predicate becomes nondet.
 2019rdf_last(L, Last) :-
 2020    rdf_is_subject(L),
 2021    !,
 2022    rdf_has(L, rdf:rest, T),
 2023    (   rdf_equal(T, rdf:nil)
 2024    ->  rdf_has(L, rdf:first, Last)
 2025    ;   rdf_last(T, Last)
 2026    ).
 2027rdf_last(L, _) :-
 2028    type_error(rdf_subject, L).
 rdf_estimate_complexity(?S, ?P, ?O, -Estimate) is det
 2033rdf_estimate_complexity(S, P, O, Estimate) :-
 2034    pre_object(O,O0,S,P),
 2035    rdf_db:rdf_estimate_complexity(S,P,O0,Estimate).
 rdf_assert_list(+PrologList, ?RDFList) is det
 rdf_assert_list(+PrologList, ?RDFList, +Graph) is det
Create an RDF list from the given Prolog List. PrologList must be a proper Prolog list and all members of the list must be acceptable as object for rdf_assert/3. If RDFList is unbound and PrologList is not empty, rdf_create_bnode/1 is used to create RDFList.
 2047rdf_assert_list(Prolog, RDF) :-
 2048    rdf_default_graph(G),
 2049    rdf_assert_list(Prolog, RDF, G).
 2050
 2051rdf_assert_list(Prolog, RDF, G) :-
 2052    must_be(list, Prolog),
 2053    rdf_transaction(rdf_assert_list_(Prolog, RDF, G)).
 2054
 2055rdf_assert_list_([], Nil, _) :-
 2056    rdf_equal(rdf:nil, Nil).
 2057rdf_assert_list_([H|T], L2, G) :-
 2058    (var(L2) -> rdf_create_bnode(L2) ; true),
 2059    rdf_assert(L2, rdf:type, rdf:'List', G),
 2060    rdf_assert(L2, rdf:first, H, G),
 2061    (   T == []
 2062    ->  rdf_assert(L2, rdf:rest, rdf:nil, G)
 2063    ;   rdf_create_bnode(T2),
 2064        rdf_assert(L2, rdf:rest, T2, G),
 2065        rdf_assert_list_(T, T2, G)
 2066    ).
 rdf_retract_list(+RDFList) is det
Retract the rdf:first, rdf:rest and rdf:type=rdf:'List' triples from all nodes reachable through rdf:rest. Note that other triples that exist on the nodes are left untouched.
 2075rdf_retract_list(L) :-
 2076    rdf_is_subject(L),
 2077    !,
 2078    rdf_transaction(rdf_retract_list_(L)).
 2079rdf_retract_list(L) :-
 2080    type_error(rdf_subject, L).
 2081
 2082:- rdf_meta
 2083    rdf_retract_list_(r). 2084
 2085rdf_retract_list_(rdf:nil) :- !.
 2086rdf_retract_list_(L) :-
 2087    rdf_retractall(L, rdf:first, _),
 2088    forall(rdf_has(L, rdf:rest, L1),
 2089           rdf_retract_list_(L1)),
 2090    rdf_retractall(L, rdf:rest, _),
 2091    rdf_retractall(L, rdf:type, rdf:'List')