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.
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   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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   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(c14n2)).  103:- use_module(library(debug)).  104:- use_module(library(error)).  105:- use_module(library(lists)).  106:- use_module(library(memfile)).  107:- reexport(library(semweb/rdf_db),
  108            except([ rdf/3,
  109                     rdf/4,
  110                     rdf_assert/3,
  111                     rdf_assert/4,
  112                     rdf_current_literal/1,
  113                     rdf_current_predicate/1,
  114                     rdf_has/3,
  115                     rdf_has/4,
  116                     rdf_update/4,
  117                     rdf_update/5,
  118                     rdf_reachable/3,
  119                     rdf_reachable/5,
  120                     rdf_retractall/3,
  121                     rdf_retractall/4,
  122                     rdf_node/1,
  123                     rdf_bnode/1,
  124                     rdf_is_literal/1,
  125                     rdf_is_resource/1,
  126                     rdf_literal_value/2,
  127                     rdf_compare/3,
  128                     rdf_estimate_complexity/4
  129                   ])
  130           ).  131:- use_module(library(sgml)).  132:- use_module(library(solution_sequences)).

  173:- multifile
  174    in_ground_type_hook/3,                  % +Type, +Input, -Lexical:atom
  175    out_type_hook/3,                        % +Type, -Output, +Lexical:atom
  176    invalid_lexical_form_hook/3.            % +Type, +Lexical, -Prolog
  177
  178:- meta_predicate
  179    parse_partial_xml(3,+,-).  180
  181:- rdf_meta
  182    rdf(r,r,o),
  183    rdf(r,r,o,r),
  184    rdf_assert(r,r,o),
  185    rdf_assert(r,r,o,r),
  186    rdf_has(r,r,o),
  187    rdf_has(r,r,o,-),
  188    rdf_update(r,r,o,t),
  189    rdf_update(r,r,o,r,t),
  190    rdf_reachable(r,r,o),
  191    rdf_reachable(r,r,o,+,-),
  192    rdf_retractall(r,r,o),
  193    rdf_retractall(r,r,o,r),
  194    {}(t),
  195    rdf_where(t),
  196    rdf_canonical_literal(o,-),
  197    rdf_lexical_form(o,-),
  198    rdf_compare(-,o,o),
  199    rdf_iri(r),
  200    rdf_is_iri(r),
  201    rdf_is_literal(o),
  202    rdf_is_name(o),
  203    rdf_is_object(o),
  204    rdf_is_predicate(r),
  205    rdf_is_subject(r),
  206    rdf_is_term(o),
  207    rdf_term(o),
  208    rdf_literal(o),
  209    rdf_name(o),
  210    rdf_object(o),
  211    rdf_estimate_complexity(r,r,o,-),
  212    rdf_assert_list(t,r),
  213    rdf_assert_list(t,r,r),
  214    rdf_last(r,o),
  215    rdf_list(r),
  216    rdf_list(r,-),
  217    rdf_length(r,-),
  218    rdf_member(o,r),
  219    rdf_nextto(o,o),
  220    rdf_nth0(?,r,o),
  221    rdf_nth1(?,r,o),
  222    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:

• Blank nodes are encoded by atoms that start with `_:`.
• IRIs appear in two notations:
  • Full IRIs are encoded by atoms that do not start with `_:`. Specifically, an IRI term is not required to follow the IRI standard grammar.
  • Abbreviated IRI notation that allows IRI prefix aliases that are registered by rdf_register_prefix/[2,3] to be used. Their notation is Alias:Local, where Alias and Local are atoms. Each abbreviated IRI is expanded by the system to a full IRI.
• Literals appear in two notations:
  • String@Lang A language-tagged string, where String is a Prolog string and Lang is an atom.
  • Value^^Type A type qualified literal. For unknown types, Value is a Prolog string. If type is known, the Prolog representations from the table below are used.

    Datatype IRI	Prolog term
    xsd:float	float
    xsd:double	float
    xsd:decimal	float (1)
    xsd:integer	integer
    XSD integer sub-types	integer
    xsd:boolean	true or false
    xsd:date	date(Y,M,D)
    xsd:dateTime	date_time(Y,M,D,HH,MM,SS) (2,3)
    xsd:gDay	integer
    xsd:gMonth	integer
    xsd:gMonthDay	month_day(M,D)
    xsd:gYear	integer
    xsd:gYearMonth	year_month(Y,M)
    xsd:time	time(HH,MM,SS) (2)

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.

  305rdf(S,P,O) :-
  306    pre_object(O,O0),
  307    rdf_db:rdf(S,P,O0),
  308    post_object(O,O0).
  309
  310rdf(S,P,O,G) :-
  311    pre_object(O,O0),
  312    pre_graph(G,G0),
  313    rdf_db:rdf(S,P,O0,G0),
  314    post_graph(G, G0),
  315    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.

  325rdf_has(S,P,O) :-
  326    pre_object(O,O0),
  327    rdf_db:rdf_has(S,P,O0),
  328    post_object(O,O0).
  329
  330rdf_has(S,P,O,RealP) :-
  331    pre_object(O,O0),
  332    rdf_db:rdf_has(S,P,O0,RealP),
  333    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 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/4 and will throw an error when used with rdf_update/3.

The argument matching the 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.

  370rdf_update(S, P, O, Action) :-
  371    rdf_update(S, P, O, _, Action).
  372rdf_update(S, P, O, G, Action) :-
  373    must_be(ground, Action),
  374    (   update_column(Action, S,P,O,G, On)
  375    ->  must_be(ground, On),
  376        arg(1, Action, Old),
  377        (   On == Old
  378        ->  true
  379        ;   rdf_transaction(rdf_update_(S, P, O, G, Action), update)
  380        )
  381    ;   domain_error(rdf_update_action, Action)
  382    ).
  383
  384update_column(subject(_),   S,_,_,_, S).
  385update_column(predicate(_), _,P,_,_, P).
  386update_column(object(_),    _,_,O,_, O).
  387update_column(graph(_),     _,_,_,G, G).
  388
  389rdf_update_(S1, P, O, G, subject(S2)) :-
  390    !,
  391    forall(rdf(S1, P, O, G),
  392           ( rdf_retractall(S1, P, O, G),
  393             rdf_assert(S2, P, O, G)
  394           )).
  395rdf_update_(S, P1, O, G, predicate(P2)) :-
  396    !,
  397    forall(rdf(S, P1, O, G),
  398           ( rdf_retractall(S, P1, O, G),
  399             rdf_assert(S, P2, O, G)
  400           )).
  401rdf_update_(S, P, O1, G, object(O2)) :-
  402    !,
  403    forall(rdf(S, P, O1, G),
  404           ( rdf_retractall(S, P, O1, G),
  405             rdf_assert(S, P, O2, G)
  406           )).
  407rdf_update_(S, P, O, G1, graph(G2)) :-
  408    !,
  409    forall(rdf(S, P, O, G1),
  410           ( rdf_retractall(S, P, O, G1),
  411             rdf_assert(S, P, O, G2)
  412           )).

 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 breath first search.

  429rdf_reachable(S,P,O) :-
  430    pre_object(O,O0),
  431    rdf_db:rdf_reachable(S,P,O0),
  432    post_object(O,O0).
  433
  434rdf_reachable(S,P,O,MaxD,D) :-
  435    pre_object(O,O0),
  436    rdf_db:rdf_reachable(S,P,O0,MaxD,D),
  437    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.

  452rdf_assert(S,P,O) :-
  453    rdf_default_graph(G),
  454    rdf_assert(S,P,O,G).
  455
  456rdf_assert(S,P,O,G) :-
  457    must_be(ground, O),
  458    pre_ground_object(O,O0),
  459    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.

  468rdf_retractall(S,P,O) :-
  469    pre_object(O,O0),
  470    rdf_db:rdf_retractall(S,P,O0).
  471
  472rdf_retractall(S,P,O,G) :-
  473    pre_object(O,O0),
  474    pre_graph(G,G0),
  475    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:

• Literal < BNode < IRI
• For literals
  • Numeric < non-numeric
  • Numeric literals are ordered by value. If both are equal, floats are ordered before integers.
  • Other data types are ordered lexicographically.
• BNodes and IRIs are ordered lexicographically.

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 >

  496rdf_compare(Diff, Left, Right) :-
  497    pre_ground_object(Left, Left0),
  498    pre_ground_object(Right, Right0),
  499    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:{...}.

  542{}(Where) :-
  543    rdf_where(Where).
  544
  545rdf_where(Var) :-
  546    var(Var),
  547    !,
  548    instantiation_error(Var).
  549rdf_where((A,B)) :-
  550    !,
  551    rdf_where(A),
  552    rdf_where(B).
  553rdf_where(Constraint) :-
  554    rdf_constraint(Constraint, Goal),
  555    !,
  556    call(Goal).
  557rdf_where(Constraint) :-
  558    existence_error(rdf_constraint, Constraint).
  559
  560% Comparison operators
  561rdf_constraint(Term >= Value,
  562               add_value_constraint(Term, >=, Value)).
  563rdf_constraint(Term >  Value,
  564               add_value_constraint(Term, >,  Value)).
  565rdf_constraint(Term == Value,
  566               add_value_constraint(Term, ==,  Value)).
  567rdf_constraint(Term <  Value,
  568               add_value_constraint(Term, <,  Value)).
  569rdf_constraint(Term =< Value,
  570               add_value_constraint(Term, =<, Value)).
  571% String selection
  572rdf_constraint(prefix(Term, Pattern),
  573               add_text_constraint(Term, prefix(PatternA))) :-
  574    atom_string(PatternA, Pattern).
  575rdf_constraint(substring(Term, Pattern),
  576               add_text_constraint(Term, substring(PatternA))) :-
  577    atom_string(PatternA, Pattern).
  578rdf_constraint(word(Term, Pattern),
  579               add_text_constraint(Term, word(PatternA))) :-
  580    atom_string(PatternA, Pattern).
  581rdf_constraint(like(Term, Pattern),
  582               add_text_constraint(Term, like(PatternA))) :-
  583    atom_string(PatternA, Pattern).
  584rdf_constraint(icase(Term, Pattern),
  585               add_text_constraint(Term, icase(PatternA))) :-
  586    atom_string(PatternA, Pattern).
  587% Lang selection
  588rdf_constraint(lang_matches(Term, Pattern),
  589               add_lang_constraint(Term, lang_matches(Pattern))).
  590
  591add_text_constraint(Var, Cond) :-
  592    var(Var),
  593    !,
  594    (   get_attr(Var, rdf11, Cond0)
  595    ->  put_attr(Var, rdf11, [Cond|Cond0])
  596    ;   put_attr(Var, rdf11, [Cond])
  597    ).
  598add_text_constraint(Text^^_Type, Cond) :-
  599    !,
  600    add_text_constraint(Text, Cond).
  601add_text_constraint(Text@_Lang, Cond) :-
  602    !,
  603    add_text_constraint(Text, Cond).
  604add_text_constraint(Var, Cond) :-
  605    eval_condition(Cond, Var).

 add_lang_constraint(?Term, +Constraint)

Add a constraint on the language of a literal

  611add_lang_constraint(Var, Constraint) :-
  612    var(Var),
  613    !,
  614    (   get_attr(Var, rdf11, Cond0)
  615    ->  put_attr(Var, rdf11, [Constraint|Cond0])
  616    ;   put_attr(Var, rdf11, [Constraint])
  617    ).
  618add_lang_constraint(_Text@Lang, Constraint) :-
  619    !,
  620    add_lang_constraint(Lang, Constraint).
  621add_lang_constraint(_Text^^_Type, _Constraint) :-
  622    !,
  623    fail.
  624add_lang_constraint(Term, Constraint) :-
  625    eval_condition(Constraint, Term).

 add_value_constraint(?Term, +Constraint, +Value)

Apply a value constraint to the RDF Term.

  631add_value_constraint(Term, Constraint, ValueIn) :-
  632    constraint_literal_value(ValueIn, Value),
  633    add_value_constraint_cann(Value, Constraint, Term).
  634
  635constraint_literal_value(Value, Value^^_Type) :-
  636    number(Value),
  637    !.
  638constraint_literal_value(Value, Literal) :-
  639    rdf_canonical_literal(Value, Literal).
  640
  641add_value_constraint_cann(RefVal^^Type, Constraint, Term) :-
  642    var(Term), var(Type),
  643    !,
  644    add_text_constraint(Term, value(Constraint, RefVal, Type)).
  645add_value_constraint_cann(RefVal^^Type, Constraint, Val^^Type2) :-
  646    !,
  647    Type = Type2,
  648    add_text_constraint(Val, value(Constraint, RefVal, Type)).
  649add_value_constraint_cann(RefVal@Lang, Constraint, Val@Lang) :-
  650    !,
  651    add_text_constraint(Val, value(Constraint, RefVal, lang(Lang))).
  652add_value_constraint_cann(RefVal^^Type, Constraint, Val) :-
  653    !,
  654    ground(Val),
  655    Val \= _@_,
  656    eval_condition(value(Constraint, RefVal, Type), Val).
  657
  658put_cond(Var, []) :-
  659    !,
  660    del_attr(Var, rdf11).
  661put_cond(Var, List) :-
  662    put_attr(Var, rdf11, List).
  663
  664eval_condition(Cond, Literal) :-
  665    text_condition(Cond),
  666    !,
  667    text_of(Literal, Text),
  668    text_condition(Cond, Text).
  669eval_condition(Cond, Literal) :-
  670    lang_condition(Cond),
  671    !,
  672    lang_of(Literal, Lang),
  673    lang_condition(Cond, Lang).
  674eval_condition(value(Comp, Ref, _Type), Value) :-
  675    (   number(Ref)
  676    ->  number(Value),
  677        compare_numeric(Comp, Ref, Value)
  678    ;   compare_std(Comp, Ref, Value)
  679    ).
  680
  681compare_numeric(<,  Ref, Value) :- Value  < Ref.
  682compare_numeric(=<, Ref, Value) :- Value =< Ref.
  683compare_numeric(==, Ref, Value) :- Value =:= Ref.
  684compare_numeric(>=, Ref, Value) :- Value >= Ref.
  685compare_numeric( >, Ref, Value) :- Value >  Ref.
  686
  687compare_std(<,  Ref, Value) :- Value  @< Ref.
  688compare_std(=<, Ref, Value) :- Value @=< Ref.
  689compare_std(==, Ref, Value) :- Value ==  Ref.
  690compare_std(>=, Ref, Value) :- Value @>= Ref.
  691compare_std( >, Ref, Value) :- Value @>  Ref.
  692
  693text_condition(prefix(_)).
  694text_condition(substring(_)).
  695text_condition(word(_)).
  696text_condition(like(_)).
  697text_condition(icase(_)).
  698
  699text_of(Literal, Text) :-
  700    atomic(Literal),
  701    !,
  702    Text = Literal.
  703text_of(Text@_Lang, Text).
  704text_of(Text^^_Type, Text).
  705
  706text_condition(prefix(Pattern), Text) :-
  707    rdf_match_label(prefix, Pattern, Text).
  708text_condition(substring(Pattern), Text) :-
  709    rdf_match_label(substring, Pattern, Text).
  710text_condition(word(Pattern), Text) :-
  711    rdf_match_label(word, Pattern, Text).
  712text_condition(like(Pattern), Text) :-
  713    rdf_match_label(like, Pattern, Text).
  714text_condition(icase(Pattern), Text) :-
  715    rdf_match_label(icase, Pattern, Text).
  716
  717lang_condition(lang_matches(_)).
  718
  719lang_of(_Text@Lang0, Lang) :-
  720    !,
  721    Lang = Lang0.
  722lang_of(Lang, Lang) :-
  723    atom(Lang).
  724
  725lang_condition(lang_matches(Pattern), Lang) :-
  726    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.

  734literal_condition(Object, Cond) :-
  735    var(Object),
  736    !,
  737    get_attr(Object, rdf11, Cond0),
  738    best_literal_cond(Cond0, Cond, Rest),
  739    put_cond(Object, Rest).
  740literal_condition(Text@_Lang, Cond) :-
  741    get_attr(Text, rdf11, Cond0),
  742    !,
  743    best_literal_cond(Cond0, Cond, Rest),
  744    put_cond(Text, Rest).
  745literal_condition(Text^^_Type, Cond) :-
  746    get_attr(Text, rdf11, Cond0),
  747    best_literal_cond(Cond0, Cond, Rest),
  748    put_cond(Text, 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.

  757best_literal_cond(Conditions, Best, Rest) :-
  758    sort(Conditions, Unique),
  759    best_literal_cond2(Unique, Best, Rest).
  760
  761best_literal_cond2(Conds, Best, Rest) :-
  762    select(Cond, Conds, Rest0),
  763    rdf10_cond(Cond, Best, Rest0, Rest),
  764    !.
  765
  766rdf10_cond(value(=<, URef, UType), Cond, Rest0, Rest) :-
  767    (   select(value(>=, LRef, LType), Rest0, Rest)
  768    ->  true
  769    ;   memberchk(value(>, LRef, LType), Rest0)
  770    ->  Rest = Rest0
  771    ),
  772    !,
  773    in_constaint_type(LType, SLType, LRef, LRef0),
  774    in_constaint_type(UType, SUType, URef, URef0),
  775    Cond = between(type(SLType, LRef0), type(SUType, URef0)).
  776rdf10_cond(value(<, URef, UType), Cond, Rest0, Rest) :-
  777    (   select(value(>=, LRef, LType), Rest0, Rest1)
  778    ->  true
  779    ;   memberchk(value(>, LRef, LType), Rest0)
  780    ->  Rest1 = Rest0
  781    ),
  782    !,
  783    Rest = [value(<, URef, UType)|Rest1],
  784    in_constaint_type(LType, SLType, LRef, LRef0),
  785    in_constaint_type(UType, SUType, URef, URef0),
  786    Cond = between(type(SLType, LRef0), type(SUType, URef0)).
  787rdf10_cond(value(Cmp, Ref, Type), Pattern, Rest, Rest) :-
  788    !,
  789    rdf10_compare(Cmp, Ref, Type, Pattern).
  790rdf10_cond(lang_matches(_), _, _, _) :- !, fail.
  791rdf10_cond(Cond, Cond, Rest, Rest).
  792
  793rdf10_compare(Cmp, Ref, Type, Pattern) :-
  794    nonvar(Type), Type = lang(Lang),
  795    !,
  796    atom_string(Ref0, Ref),
  797    rdf10_lang_cond(Cmp, Ref0, Lang, Pattern).
  798rdf10_compare(Cmp, Ref, Type, Pattern) :-
  799    in_constaint_type(Type, SType, Ref, Ref0),
  800    rdf10_type_cond(Cmp, Ref0, SType, Pattern).
  801
  802rdf10_lang_cond( <, Ref, Lang, lt(lang(Lang,Ref))).
  803rdf10_lang_cond(=<, Ref, Lang, le(lang(Lang,Ref))).
  804rdf10_lang_cond(==, Ref, Lang, eq(lang(Lang,Ref))).
  805rdf10_lang_cond(>=, Ref, Lang, ge(lang(Lang,Ref))).
  806rdf10_lang_cond(>,  Ref, Lang, gt(lang(Lang,Ref))).
  807
  808rdf10_type_cond( <, Ref, Type, lt(type(Type,Ref))).
  809rdf10_type_cond(=<, Ref, Type, le(type(Type,Ref))).
  810rdf10_type_cond(==, Ref, Type, eq(type(Type,Ref))).
  811rdf10_type_cond(>=, Ref, Type, ge(type(Type,Ref))).
  812rdf10_type_cond( >, Ref, Type, gt(type(Type,Ref))).

 in_constaint_type(?Type, -SType, ++Val, -Val0)

  817in_constaint_type(Type, SType, Val, Val0) :-
  818    nonvar(Type), ground(Val),
  819    !,
  820    SType = Type,
  821    in_ground_type(Type, Val, Val0).
  822in_constaint_type(Type, SType, Val, Val0) :-
  823    var(Type), number(Val),
  824    !,
  825    (   integer(Val)
  826    ->  rdf_equal(SType, xsd:integer),
  827        in_ground_type(xsd:integer, Val, Val0)
  828    ;   float(Val)
  829    ->  rdf_equal(SType, xsd:double),
  830        in_ground_type(xsd:double, Val, Val0)
  831    ;   assertion(fail)
  832    ).

 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.

  840literal_class(Term, Class) :-
  841    get_attr(Term, rdf11, Conds),
  842    select(Cond, Conds, Rest),
  843    lang_condition(Cond),
  844    !,
  845    Term = Text@Lang,
  846    put_attr(Lang, rdf11, [Cond]),
  847    put_cond(Text, Rest),
  848    (   var(Text)
  849    ->  true
  850    ;   atom_string(Text2, Text)
  851    ),
  852    Class = lang(Lang, Text2).

 attr_unify_hook(+AttributeValue, +Value)

  856attr_unify_hook(Cond, Value) :-
  857    get_attr(Value, rdf11, Cond2),
  858    !,
  859    append(Cond, Cond2, CondJ),
  860    sort(CondJ, Unique),
  861    put_cond(Value, Unique).
  862attr_unify_hook(Cond, Text^^_Type) :-
  863    var(Text),
  864    !,
  865    put_cond(Text, Cond).
  866attr_unify_hook(Cond, Text@Lang) :-
  867    var(Text), var(Lang),
  868    !,
  869    partition(lang_condition, Cond, LangCond, TextCond),
  870    put_cond(Text, TextCond),
  871    put_cond(Lang, LangCond).
  872attr_unify_hook(Cond, Value) :-
  873    sort(Cond, Unique),
  874    propagate_conditions(Unique, Value).
  875
  876propagate_conditions([], _).
  877propagate_conditions([H|T], Val) :-
  878    propagate_condition(H, Val),
  879    propagate_conditions(T, Val).
  880
  881propagate_condition(value(Comp, Ref, Type), Value) :-
  882    !,
  883    (   Value = Plain^^VType
  884    ->  VType = Type
  885    ;   Plain = Value
  886    ),
  887    cond_compare(Comp, Ref, Plain).
  888propagate_condition(lang_matches(Pattern), Value) :-
  889    !,
  890    (   Value = _@Lang
  891    ->  true
  892    ;   Lang = Value
  893    ),
  894    rdf_db:lang_matches(Lang, Pattern).
  895propagate_condition(Cond, Value) :-
  896    Cond =.. [Name|Args],
  897    Constraint =.. [Name,Value|Args],
  898    rdf_constraint(Constraint, Continuation),
  899    call(Continuation).
  900
  901cond_compare(>,  Ref, Value) :- Value @>  Ref.
  902cond_compare(>=, Ref, Value) :- Value @>= Ref.
  903cond_compare(==, Ref, Value) :- Value ==  Ref.
  904cond_compare(=<, Ref, Value) :- Value @=< Ref.
  905cond_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.

  915:- create_prolog_flag(rdf_default_graph, default,
  916                      [ type(atom),
  917                        keep(true)
  918                      ]).  919
  920rdf_default_graph(Graph) :-
  921    current_prolog_flag(rdf_default_graph, Graph).
  922rdf_default_graph(Old, New) :-
  923    current_prolog_flag(rdf_default_graph, Old),
  924    (   New == Old
  925    ->  true
  926    ;   set_prolog_flag(rdf_default_graph, New)
  927    ).
  928
  929
  930pre_graph(G, _G0) :-
  931    var(G),
  932    !.
  933pre_graph(G, G) :-
  934    atom(G),
  935    !.
  936pre_graph(G, _) :-
  937    type_error(rdf_graph, G).
  938
  939post_graph(G, G0:_) :-
  940    !,
  941    G = G0.
  942post_graph(G, G).
  943
  944
  945pre_object(Literal, literal(Cond, Value)) :-
  946    literal_condition(Literal, Cond),
  947    !,
  948    debug(literal_index, 'Search literal using ~p', [literal(Cond, Value)]),
  949    literal_value0(Literal, Value).
  950pre_object(Literal, literal(Value)) :-
  951    literal_class(Literal, Value),
  952    !,
  953    debug(literal_index, 'Search literal using ~p', [literal(Value)]).
  954pre_object(Var, _Var) :-
  955    var(Var),
  956    !.
  957pre_object(Atom, URI) :-
  958    atom(Atom),
  959    \+ boolean(Atom),
  960    !,
  961    URI = Atom.
  962pre_object(Val@Lang, literal(lang(Lang, Val0))) :-
  963    !,
  964    in_lang_string(Val, Val0).
  965pre_object(Val^^Type, literal(Literal)) :-
  966    !,
  967    in_type(Type, Val, Type0, Val0),
  968    (   var(Type0), var(Val0)
  969    ->  true
  970    ;   Literal = type(Type0, Val0)
  971    ).
  972pre_object(Obj, Val0) :-
  973    ground(Obj),
  974    !,
  975    pre_ground_object(Obj, Val0).
  976pre_object(Obj, _) :-
  977    type_error(rdf_object, Obj).
  978
  979literal_value0(Var, _) :-
  980    var(Var),
  981    !.
  982literal_value0(_ @Lang, lang(Lang, _)).
  983literal_value0(_^^Type, type(Type, _)).

 pre_ground_object(+Object, -RDF) is det

Convert between a Prolog value and an RDF value for rdf_assert/3 and friends. Auto-conversion:

• Integer Converted to Integer^^xsd:integer
• Float Converted to Float^^xsd:double
• String Converted to String^^xsd:string
• true Converted to true^^xsd:boolean
• false Converted to false^^xsd:boolean
• date(Y,M,D) Converted to date(Y,M,D)^^xsd:date
• date_time(Y,M,D,HH,MM,SS) Converted to date_time(Y,M,D,HH,MM,SS)^^xsd:dateTime
• date_time(Y,M,D,HH,MM,SS,TZ) Converted to date_time(Y,M,D,HH,MM,SS,TZ)^^xsd:dateTime
• month_day(M,D) Converted to month_day(M,D)^^xsd:gMonthDay
• year_month(Y,M) Converted to year_month(Y,M)^^xsd:gYearMonth
• time(HH,MM,SS) Converted to time(HH,MM,SS)^^xsd:time
• Text@Lang Converted to Text@Lang. Uses canonical (lowercase) lang. Text is converted into an atom.
• Value^^Type Typed conversion. The translation of Value depends on Type:
  • Numeric types
  • Boolean
  • Date types
• Atom All atoms except for true and false are considered URIs.

 1026:- rdf_meta
 1027    pre_ground_object(+, o). 1028
 1029% Interpret Prolog integer as xsd:integer.
 1030pre_ground_object(Int, Object) :-
 1031    integer(Int),
 1032    !,
 1033    rdf_equal(Object, literal(type(xsd:integer, Atom))),
 1034    atom_number(Atom, Int).
 1035% Interpret Prolog floating-point value as xsd:double.
 1036pre_ground_object(Float, Object) :-
 1037    float(Float),
 1038    !,
 1039    rdf_equal(Object, literal(type(xsd:double, Atom))),
 1040    xsd_number_string(Float, String),
 1041    atom_string(Atom, String).
 1042% Interpret SWI string as xsd:string.
 1043pre_ground_object(String, Object) :-
 1044    string(String),
 1045    !,
 1046    rdf_equal(Object, literal(type(xsd:string, Atom))),
 1047    atom_string(Atom, String).
 1048% Interpret `false' and `true' as the Boolean values.
 1049pre_ground_object(false, literal(type(xsd:boolean, false))) :- !.
 1050pre_ground_object(true, literal(type(xsd:boolean, true))) :- !.
 1051% Interpret date(Y,M,D) as xsd:date,
 1052%           date_time(Y,M,D,HH,MM,SS) as xsd:dateTime,
 1053%           date_time(Y,M,D,HH,MM,SS,TZ) as xsd:dateTime,
 1054%           month_day(M,D) as xsd:gMonthDay,
 1055%           year_month(Y,M) as xsd:gYearMonth, and
 1056%           time(HH,MM,SS) as xsd:time.
 1057pre_ground_object(Term, literal(type(Type, Atom))) :-
 1058    xsd_date_time_term(Term),
 1059    !,
 1060    xsd_time_string(Term, Type, Atom).
 1061pre_ground_object(Val@Lang,  literal(lang(Lang0, Val0))) :-
 1062    !,
 1063    downcase_atom(Lang, Lang0),
 1064    in_lang_string(Val, Val0).
 1065pre_ground_object(Val^^Type, literal(type(Type0, Val0))) :-
 1066    !,
 1067    in_type(Type, Val, Type0, Val0).
 1068pre_ground_object(Atom, URI) :-
 1069    atom(Atom),
 1070    !,
 1071    URI = Atom.
 1072%pre_ground_object(NS:Local, URI) :-            % still leaves S and P.
 1073%       atom(NS), atom(Local), !,
 1074%       rdf_global_id(NS:Local, URI).
 1075pre_ground_object(literal(Lit0), literal(Lit)) :-
 1076    old_literal(Lit0, Lit),
 1077    !.
 1078pre_ground_object(Value, _) :-
 1079    type_error(rdf_object, Value).
 1080
 1081xsd_date_time_term(date(_,_,_)).
 1082xsd_date_time_term(date_time(_,_,_,_,_,_)).
 1083xsd_date_time_term(date_time(_,_,_,_,_,_,_)).
 1084xsd_date_time_term(month_day(_,_)).
 1085xsd_date_time_term(year_month(_,_)).
 1086xsd_date_time_term(time(_,_,_)).
 1087
 1088old_literal(Lit0, Lit) :-
 1089    old_literal(Lit0),
 1090    !,
 1091    Lit = Lit0.
 1092old_literal(Atom, Lit) :-
 1093    atom(Atom),
 1094    rdf_equal(xsd:string, XSDString),
 1095    Lit = type(XSDString, Atom).
 1096
 1097old_literal(type(Type, Value)) :-
 1098    atom(Type), atom(Value).
 1099old_literal(lang(Lang, Value)) :-
 1100    atom(Lang), atom(Value).
 1101
 1102in_lang_string(Val, Val0) :-
 1103    atomic(Val),
 1104    !,
 1105    atom_string(Val0, Val).
 1106in_lang_string(_, _).
 1107
 1108in_type(Type, Val, Type, Val0) :-
 1109    nonvar(Type), ground(Val),
 1110    !,
 1111    in_ground_type(Type, Val, Val0).
 1112in_type(VarType, Val, VarType, Val0) :-
 1113    ground(Val),
 1114    \+ catch(xsd_number_string(_, Val), _, fail),
 1115    !,
 1116    atom_string(Val0, Val).
 1117in_type(_, _, _, _).
 1118
 1119:- rdf_meta
 1120    in_ground_type(r,?,?),
 1121    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.

 1129in_ground_type(Type, Input, Lex) :-
 1130    \+ string(Input),
 1131    in_ground_type_hook(Type, Input, Lex),
 1132    !.
 1133in_ground_type(IntType, Val, Val0) :-
 1134    xsd_numerical(IntType, Domain, PrologType),
 1135    !,
 1136    in_number(PrologType, Domain, IntType, Val, Val0).
 1137in_ground_type(xsd:boolean, Val, Val0) :-
 1138    !,
 1139    (   in_boolean(Val, Val0)
 1140    ->  true
 1141    ;   type_error(rdf_boolean, Val)
 1142    ).
 1143in_ground_type(rdf:langString, _Val0, _) :-
 1144    !,
 1145    domain_error(rdf_data_type, rdf:langString).
 1146in_ground_type(DateTimeType, Val, Val0) :-
 1147    xsd_date_time_type(DateTimeType),
 1148    !,
 1149    in_date_time(DateTimeType, Val, Val0).
 1150in_ground_type(rdf:'XMLLiteral', Val, Val0) :-
 1151    !,
 1152    in_xml_literal(xml, Val, Val0).
 1153in_ground_type(rdf:'HTML', Val, Val0) :-
 1154    !,
 1155    in_xml_literal(html, Val, Val0).
 1156in_ground_type(_Unknown, Val, Val0) :-
 1157    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.

 1164:- rdf_meta
 1165    in_date_time(r,+,-). 1166
 1167in_date_time(Type, Text, Text0) :-
 1168    atom(Text),
 1169    !,
 1170    xsd_time_string(_, Type, Text),
 1171    Text0 = Text.
 1172in_date_time(Type, Text, Text0) :-
 1173    string(Text),
 1174    !,
 1175    xsd_time_string(_, Type, Text),
 1176    atom_string(Text0, Text).
 1177in_date_time(xsd:dateTime, Stamp, Text0) :-
 1178    number(Stamp),
 1179    !,
 1180    format_time(atom(Text0), '%FT%T%:z', Stamp).
 1181in_date_time(Type, Term, Text0) :-
 1182    !,
 1183    xsd_time_string(Term, Type, String),
 1184    atom_string(Text0, String).

 in_boolean(?NonCanonical, ?Canonical)

True when Canonical is the canonical boolean for NonCanonical.

 1191in_boolean(true,    true).
 1192in_boolean(false,   false).
 1193in_boolean("true",  true).
 1194in_boolean("false", false).
 1195in_boolean(1,       true).
 1196in_boolean(0,       false).
 1197
 1198boolean(false).
 1199boolean(true).

 in_number(+PrologType, +Domain, +XSDType, +Value, -Lexical)

Lexical is the lexical representation for Value.

Errors

- type_error(PrologType, Value)

- domain_error(XSDType, Value)

 1208in_number(integer, Domain, XSDType, Val, Val0) :-
 1209    integer(Val),
 1210    !,
 1211    check_integer_domain(Domain, XSDType, Val),
 1212    atom_number(Val0, Val).
 1213in_number(integer, Domain, XSDType, Val, Val0) :-
 1214    atomic(Val),
 1215    atom_number(Val, Num),
 1216    integer(Num),
 1217    !,
 1218    check_integer_domain(Domain, XSDType, Num),
 1219    atom_number(Val0, Num).
 1220in_number(double, _Domain, _, Val, Val0) :-
 1221    number(Val),
 1222    !,
 1223    ValF is float(Val),
 1224    xsd_number_string(ValF, ValS),
 1225    atom_string(Val0, ValS).
 1226in_number(double, _Domain, _, Val, Val0) :-
 1227    atomic(Val),
 1228    xsd_number_string(Num, Val),
 1229    ValF is float(Num),
 1230    !,
 1231    xsd_number_string(ValF, ValS),
 1232    atom_string(Val0, ValS).
 1233in_number(PrologType, _, _, Val, _) :-
 1234    type_error(PrologType, Val).
 1235
 1236check_integer_domain(PLType, _, Val) :-
 1237    is_of_type(PLType, Val),
 1238    !.
 1239check_integer_domain(_, XSDType, Val) :-
 1240    domain_error(XSDType, Val).
 1241
 1242error:has_type(nonpos, T):-
 1243    integer(T),
 1244    T =< 0.
 1245
 1246%check_integer_domain(between(Low, High), XSDType, Val) :-
 1247%       (   between(Low, High, Val)
 1248%       ->  true
 1249%       ;   domain_error(XSDType, Val)
 1250%       ).
 1251%check_integer_domain(integer, _, _).

 xsd_numerical(?URI, ?TypeCheck, ?PrologType)

 1255:- rdf_meta
 1256    xsd_numerical(r, ?, ?). 1257
 1258xsd_numerical(xsd:byte,               between(-128,127),               integer).
 1259xsd_numerical(xsd:double,             float,                           double).
 1260xsd_numerical(xsd:decimal,            float,                           double).
 1261xsd_numerical(xsd:float,              float,                           double).
 1262xsd_numerical(xsd:int,                between(-2147483648,2147483647), integer).
 1263xsd_numerical(xsd:integer,            integer,                         integer).
 1264xsd_numerical(xsd:long,               between(-9223372036854775808,
 1265                                               9223372036854775807),   integer).
 1266xsd_numerical(xsd:negativeInteger,    negative_integer,                integer).
 1267xsd_numerical(xsd:nonNegativeInteger, nonneg,                          integer).
 1268xsd_numerical(xsd:nonPositiveInteger, nonpos,                          integer).
 1269xsd_numerical(xsd:positiveInteger,    positive_integer,                integer).
 1270xsd_numerical(xsd:short,              between(-32768,32767),           integer).
 1271xsd_numerical(xsd:unsignedByte,       between(0,255),                  integer).
 1272xsd_numerical(xsd:unsignedInt,        between(0,4294967295),           integer).
 1273xsd_numerical(xsd:unsignedLong,       between(0,18446744073709551615), integer).
 1274xsd_numerical(xsd:unsignedShort,      between(0,65535),                integer).

 xsd_date_time_type(?URI)

True when URI is an XSD date or time type.

 1280:- rdf_meta
 1281    xsd_date_time_type(r). 1282
 1283xsd_date_time_type(xsd:date).
 1284xsd_date_time_type(xsd:dateTime).
 1285xsd_date_time_type(xsd:gDay).
 1286xsd_date_time_type(xsd:gMonth).
 1287xsd_date_time_type(xsd:gMonthDay).
 1288xsd_date_time_type(xsd:gYear).
 1289xsd_date_time_type(xsd:gYearMonth).
 1290xsd_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?

 1300in_xml_literal(Type, Val, Val0) :-
 1301    xml_is_dom(Val),
 1302    !,
 1303    write_xml_literal(Type, Val, Val0).
 1304in_xml_literal(xml, Val, Val0) :-
 1305    parse_partial_xml(load_xml, Val, DOM),
 1306    write_xml_literal(xml, DOM, Val0).
 1307in_xml_literal(html, Val, Val0) :-
 1308    parse_partial_xml(load_html, Val, DOM),
 1309    write_xml_literal(html, DOM, Val0).
 1310
 1311parse_partial_xml(Parser, Val, DOM) :-
 1312    setup_call_cleanup(
 1313        new_memory_file(MF),
 1314        (   setup_call_cleanup(
 1315                open_memory_file(MF, write, Out),
 1316                format(Out, "<xml>~w</xml>", [Val]),
 1317                close(Out)),
 1318            setup_call_cleanup(
 1319                open_memory_file(MF, read, In),
 1320                call(Parser, stream(In), [element(xml, _, DOM)], []),
 1321                close(In))
 1322        ),
 1323        free_memory_file(MF)).
 1324
 1325
 1326write_xml_literal(xml, DOM, Text) :-
 1327    with_output_to(atom(Text),
 1328                   xml_write_canonical(current_output, DOM, [])).
 1329write_xml_literal(html, DOM, Text) :-
 1330    with_output_to(atom(Text),
 1331                   html_write(current_output, DOM,
 1332                              [ header(false),
 1333                                layout(false)
 1334                              ])).

 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 Term	Datatype IRI
float	xsd:double
integer	xsd:integer
string	xsd:string
true or false	xsd: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'.

 1362rdf_canonical_literal(In, Literal) :-
 1363    ground(In),
 1364    !,
 1365    pre_ground_object(In, DBTerm),
 1366    post_object(Literal, DBTerm).
 1367rdf_canonical_literal(In, _) :-
 1368    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.

• String^^Type
• String@Lang

 1381%       For example,
 1382%
 1383%       ==
 1384%       ?- rdf_lexical_form(2.3^^xsd:double, L).
 1385%       L = "2.3E0"^^'http://www.w3.org/2001/XMLSchema#double'.
 1386%       ==
 1387
 1388rdf_lexical_form(Literal, Lexical) :-
 1389    pre_ground_object(Literal, literal(Lit0)),
 1390    !,
 1391    text_of0(Lit0, Lexical).
 1392rdf_lexical_form(Literal, _) :-
 1393    type_error(rdf_literal, Literal).
 1394
 1395text_of0(type(TypeA, LexicalA), LexicalS^^TypeA) :-
 1396    atom_string(LexicalA, LexicalS).
 1397text_of0(lang(LangA, LexicalA), LexicalS@LangA) :-
 1398    atom_string(LexicalA, LexicalS).
 1399
 1400
 1401                 /*******************************
 1402                 *       POST PROCESSING        *
 1403                 *******************************/
 1404
 1405:- rdf_meta
 1406    post_object(o,o),
 1407    out_type(r,-,+). 1408
 1409post_object(Val, _) :-
 1410    ground(Val),
 1411    !.                 % already specified and matched
 1412post_object(URI, URI0) :-
 1413    atom(URI0),
 1414    !,
 1415    URI = URI0.
 1416post_object(Val@Lang, literal(lang(Lang, Val0))) :-
 1417    nonvar(Lang),          % lang(Lang,Text) returns var(Lang) if no lang
 1418    !,
 1419    atom_string(Val0, Val).
 1420post_object(Val^^Type, literal(type(Type, Val0))) :-
 1421    !,
 1422    out_type(Type, Val, Val0).
 1423post_object(Val^^xsd:string, literal(Plain)) :-
 1424    !,
 1425    atomic(Plain),
 1426    atom_string(Plain, Val).
 1427post_object(Val@Lang, literal(_, lang(Lang, Val0))) :-
 1428    nonvar(Lang),
 1429    !,
 1430    atom_string(Val0, Val).
 1431post_object(Val^^Type, literal(_, type(Type, Val0))) :-
 1432    !,
 1433    out_type(Type, Val, Val0).
 1434post_object(Val^^xsd:string, literal(_, Plain)) :-
 1435    atomic(Plain),
 1436    atom_string(Plain, Val).
 1437
 1438out_type(xsd:string, Val, Val0) :-     % catches unbound type too
 1439    !,
 1440    atom_string(Val0, Val).
 1441out_type(Type, Val, Val0) :-
 1442    out_type_hook(Type, Val, Val0),
 1443    !.
 1444out_type(IntType, Val, Val0) :-
 1445    xsd_numerical(IntType, _Domain, _BasicType),
 1446    !,
 1447    xsd_number_string(Val, Val0).
 1448out_type(DateTimeType, Val, Val0) :-
 1449    xsd_date_time_type(DateTimeType),
 1450    !,
 1451    out_date_time(DateTimeType, Val, Val0).
 1452out_type(xsd:boolean, Val, Val0) :-
 1453    !,
 1454    Val = Val0.
 1455out_type(rdf:'XMLLiteral', XML, DOM) :-
 1456    xml_is_dom(DOM),
 1457    !,
 1458    with_output_to(string(XML),
 1459                   xml_write(DOM, [header(false)])).
 1460out_type(_Unknown, Val, Val0) :-
 1461    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.

 1469out_date_time(Type, Prolog, Lexical) :-
 1470    catch(xsd_time_string(Prolog, Type, Lexical),
 1471          error(_,_),
 1472          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.

 1482                 /*******************************
 1483                 *          ENUMERATION         *
 1484                 *******************************/

 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.

 1493rdf_term(N) :-
 1494    ground(N),
 1495    !,
 1496    pre_object(N, N0),
 1497    visible_term(N0).
 1498rdf_term(N) :-
 1499    gen_term(N).
 1500
 1501gen_term(N) :-
 1502    resource(N),
 1503    visible_term(N).
 1504gen_term(O) :-                          % performs double conversion!
 1505    rdf_literal(O),
 1506    (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.

 1514rdf_literal(Term) :-
 1515    ground(Term),
 1516    !,
 1517    pre_ground_object(Term, Object),
 1518    (rdf_db:rdf(_,_,Object)->true).
 1519rdf_literal(Term) :-
 1520    pre_object(Term,literal(Lit0)),
 1521    rdf_db:rdf_current_literal(Lit0),
 1522    (rdf_db:rdf(_,_,literal(Lit0))->true),
 1523    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.

 1530rdf_bnode(BNode) :-
 1531    atom(BNode),
 1532    !,
 1533    current_bnode(BNode).
 1534rdf_bnode(BNode) :-
 1535    rdf_db:rdf_resource(BNode),
 1536    current_bnode(BNode).
 1537
 1538current_bnode(BNode) :-
 1539    rdf_is_bnode(BNode),
 1540    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.

 1547rdf_iri(IRI) :-
 1548    atom(IRI),
 1549    !,
 1550    \+ rdf_is_bnode(IRI),
 1551    visible_term(IRI).
 1552rdf_iri(IRI) :-
 1553    resource(IRI),
 1554    \+ rdf_is_bnode(IRI),
 1555    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.

 1562rdf_name(Name) :-
 1563    atom(Name), \+ boolean(Name),
 1564    !,
 1565    \+ rdf_is_bnode(Name),
 1566    visible_term(Name).
 1567rdf_name(Name) :-
 1568    ground(Name),
 1569    !,
 1570    pre_ground_object(Name, Name0),
 1571    (rdf_db:rdf(_,_,Name0)->true).
 1572rdf_name(Name) :-
 1573    rdf_iri(Name).
 1574rdf_name(Name) :-
 1575    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.

 1590rdf_predicate(P) :-
 1591    atom(P),
 1592    !,
 1593    (rdf(_,P,_) -> true).
 1594rdf_predicate(P) :-
 1595    rdf_db:rdf_current_predicate(P),
 1596    (rdf(_,P,_) -> true).

 rdf_object(?O) is nondet

True when O is a currently known object, i.e. it appeasr 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.

 1605rdf_object(O) :-
 1606    ground(O),
 1607    !,
 1608    (   atom(O), \+ boolean(O)
 1609    ->  (rdf_db:rdf(_,_,O) -> true)
 1610    ;   rdf_literal(O)
 1611    ).
 1612rdf_object(O) :-
 1613    rdf_db:rdf_resource(O),
 1614    (rdf_db:rdf(_,_,O) -> true).
 1615rdf_object(O) :-
 1616    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.

 1623rdf_node(N) :-
 1624    var(N),
 1625    !,
 1626    gen_node(N).
 1627rdf_node(N) :-
 1628    pre_ground_object(N, N0),
 1629    visible_node(N0).
 1630
 1631gen_node(N) :-
 1632    rdf_db:rdf_resource(N),
 1633    visible_node(N).
 1634gen_node(O) :-                          % performs double conversion!
 1635    rdf_literal(O),
 1636    (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.

 1644resource(R) :-
 1645    var(R),
 1646    !,
 1647    gen_resource(R).
 1648resource(R) :-
 1649    rdf_db:rdf_resource(R),
 1650    !.
 1651resource(R) :-
 1652    rdf_db:rdf_current_predicate(R),
 1653    !.
 1654
 1655gen_resource(R) :-
 1656    rdf_db:rdf_resource(R).
 1657gen_resource(R) :-
 1658    rdf_db:rdf_current_predicate(R),
 1659    \+ rdf_db:rdf_resource(R).
 1660
 1661visible_node(Term) :-
 1662    atom(Term),
 1663    !,
 1664    (   rdf_db:rdf(Term,_,_)
 1665    ;   rdf_db:rdf(_,_,Term)
 1666    ),
 1667    !.
 1668visible_node(Term) :-
 1669    rdf_db:rdf(_,_,Term).
 1670
 1671visible_term(Term) :-
 1672    atom(Term),
 1673    !,
 1674    (   rdf_db:rdf(Term,_,_)
 1675    ;   rdf_db:rdf(_,Term,_)
 1676    ;   rdf_db:rdf(_,_,Term)
 1677    ),
 1678    !.
 1679visible_term(Term) :-
 1680    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.

 1688rdf_create_bnode(BNode) :-
 1689    var(BNode),
 1690    !,
 1691    rdf_db:rdf_bnode(BNode).
 1692rdf_create_bnode(BNode) :-
 1693    uninstantiation_error(BNode).
 1694
 1695
 1696                 /*******************************
 1697                 *         TYPE CHECKING        *
 1698                 *******************************/

 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).

 1713rdf_is_iri(IRI) :-
 1714    atom(IRI),
 1715    \+ 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).

 1743rdf_is_literal(Literal) :-
 1744    literal_form(Literal),
 1745    !,
 1746    ground(Literal).
 1747
 1748literal_form(_@_).
 1749literal_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).

 1760rdf_is_name(T) :- rdf_is_iri(T), !.
 1761rdf_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.

 1775rdf_is_object(T) :- rdf_is_subject(T), !.
 1776rdf_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.

 1789rdf_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).

 1805rdf_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).

 1815rdf_is_term(N) :- rdf_is_subject(N), !.
 1816rdf_is_term(N) :- rdf_is_literal(N).
 1817
 1818
 1819                 /*******************************
 1820                 *          COLLECTIONS         *
 1821                 *******************************/

 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).

 1833rdf_list(L) :-
 1834    var(L),
 1835    !,
 1836    rdf_has(L, rdf:first, _),
 1837    \+ rdf_has(_, rdf:rest, L),
 1838    rdf_list_g(L).
 1839rdf_list(L) :-
 1840    rdf_list_g(L),
 1841    !.
 1842
 1843rdf_list_g(rdf:nil) :- !.
 1844rdf_list_g(L) :-
 1845    once(rdf_has(L, rdf:first, _)),
 1846    rdf_has(L, rdf:rest, Rest),
 1847    (   rdf_equal(rdf:nil, Rest)
 1848    ->  true
 1849    ;   rdf_list_g(Rest)
 1850    ).

 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.

 1859rdf_list(RDFList, Prolog) :-
 1860    rdf_is_subject(RDFList),
 1861    !,
 1862    rdf_list_to_prolog(RDFList, Prolog).
 1863rdf_list(RDFList, _Prolog) :-
 1864    type_error(rdf_subject, RDFList).
 1865
 1866:- rdf_meta
 1867    rdf_list_to_prolog(r,-). 1868
 1869rdf_list_to_prolog(rdf:nil, Prolog) :-
 1870    !,
 1871    Prolog = [].
 1872rdf_list_to_prolog(RDF, [H|T2]) :-
 1873    (   rdf_has(RDF, rdf:first, H0),
 1874        rdf_has(RDF, rdf:rest, T1)
 1875    *-> H = H0,
 1876        rdf_list_to_prolog(T1, T2)
 1877    ;   type_error(rdf_list, RDF)
 1878    ).