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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   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
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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(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:- use_module(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           ).

  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:

• 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.

  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:

• 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 >

  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:

• 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.

 1057:- rdf_meta
 1058    pre_ground_object(+, o). 1059
 1060pre_ground_object(Val@Lang,  literal(lang(Lang0, Val0))) :-
 1061    !,
 1062    downcase_atom(Lang, Lang0),
 1063    in_lang_string(Val, Val0).
 1064pre_ground_object(Val^^Type, literal(type(Type0, Val0))) :-
 1065    !,
 1066    in_type(Type, Val, Type0, Val0).
 1067pre_ground_object(literal(Lit0), literal(Lit)) :-
 1068    old_literal(Lit0, Lit),
 1069    !.
 1070% Interpret `false' and `true' as the Boolean values.
 1071pre_ground_object(false, literal(type(xsd:boolean, false))) :- !.
 1072pre_ground_object(true, literal(type(xsd:boolean, true))) :- !.
 1073pre_ground_object(Atom, URI) :-
 1074    atom(Atom),
 1075    !,
 1076    URI = Atom.
 1077% Interpret Prolog integer as xsd:integer.
 1078pre_ground_object(Int, Object) :-
 1079    integer(Int),
 1080    !,
 1081    rdf_equal(Object, literal(type(xsd:integer, Atom))),
 1082    atom_number(Atom, Int).
 1083% Interpret Prolog floating-point value as xsd:double.
 1084pre_ground_object(Float, Object) :-
 1085    float(Float),
 1086    !,
 1087    rdf_equal(Object, literal(type(xsd:double, Atom))),
 1088    xsd_number_string(Float, String),
 1089    atom_string(Atom, String).
 1090% Interpret SWI string as xsd:string.
 1091pre_ground_object(String, Object) :-
 1092    string(String),
 1093    !,
 1094    rdf_equal(Object, literal(type(xsd:string, Atom))),
 1095    atom_string(Atom, String).
 1096% Interpret date(Y,M,D) as xsd:date,
 1097%           date_time(Y,M,D,HH,MM,SS) as xsd:dateTime,
 1098%           date_time(Y,M,D,HH,MM,SS,TZ) as xsd:dateTime,
 1099%           month_day(M,D) as xsd:gMonthDay,
 1100%           year_month(Y,M) as xsd:gYearMonth, and
 1101%           time(HH,MM,SS) as xsd:time.
 1102pre_ground_object(Term, literal(type(Type, Atom))) :-
 1103    xsd_date_time_term(Term),
 1104    !,
 1105    xsd_time_string(Term, Type, String),
 1106    atom_string(Atom, String).
 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(decimal, _Domain, _, Val, Val0) :-
 1263    number(Val),
 1264    !,
 1265    ValF is float(Val),
 1266    atom_number(Val0, ValF).
 1267in_number(decimal, _Domain, _, Val, Val0) :-
 1268    atomic(Val),
 1269    xsd_number_string(Num, Val),
 1270    ValF is float(Num),
 1271    !,
 1272    atom_number(Val0, ValF).
 1273in_number(PrologType, _, _, Val, _) :-
 1274    type_error(PrologType, Val).
 1275
 1276check_integer_domain(PLType, _, Val) :-
 1277    is_of_type(PLType, Val),
 1278    !.
 1279check_integer_domain(_, XSDType, Val) :-
 1280    domain_error(XSDType, Val).
 1281
 1282error:has_type(nonpos, T):-
 1283    integer(T),
 1284    T =< 0.
 1285
 1286%check_integer_domain(between(Low, High), XSDType, Val) :-
 1287%       (   between(Low, High, Val)
 1288%       ->  true
 1289%       ;   domain_error(XSDType, Val)
 1290%       ).
 1291%check_integer_domain(integer, _, _).

 xsd_numerical(?URI, ?TypeCheck, ?PrologType)

 1295:- rdf_meta
 1296    xsd_numerical(r, ?, ?). 1297
 1298xsd_numerical(xsd:byte,               between(-128,127),               integer).
 1299xsd_numerical(xsd:double,             float,                           double).
 1300xsd_numerical(xsd:decimal,            float,                           decimal).
 1301xsd_numerical(xsd:float,              float,                           double).
 1302xsd_numerical(xsd:int,                between(-2147483648,2147483647), integer).
 1303xsd_numerical(xsd:integer,            integer,                         integer).
 1304xsd_numerical(xsd:long,               between(-9223372036854775808,
 1305                                               9223372036854775807),   integer).
 1306xsd_numerical(xsd:negativeInteger,    negative_integer,                integer).
 1307xsd_numerical(xsd:nonNegativeInteger, nonneg,                          integer).
 1308xsd_numerical(xsd:nonPositiveInteger, nonpos,                          integer).
 1309xsd_numerical(xsd:positiveInteger,    positive_integer,                integer).
 1310xsd_numerical(xsd:short,              between(-32768,32767),           integer).
 1311xsd_numerical(xsd:unsignedByte,       between(0,255),                  integer).
 1312xsd_numerical(xsd:unsignedInt,        between(0,4294967295),           integer).
 1313xsd_numerical(xsd:unsignedLong,       between(0,18446744073709551615), integer).
 1314xsd_numerical(xsd:unsignedShort,      between(0,65535),                integer).

 xsd_date_time_type(?URI)

True when URI is an XSD date or time type.

 1320:- rdf_meta
 1321    xsd_date_time_type(r). 1322
 1323xsd_date_time_type(xsd:date).
 1324xsd_date_time_type(xsd:dateTime).
 1325xsd_date_time_type(xsd:gDay).
 1326xsd_date_time_type(xsd:gMonth).
 1327xsd_date_time_type(xsd:gMonthDay).
 1328xsd_date_time_type(xsd:gYear).
 1329xsd_date_time_type(xsd:gYearMonth).
 1330xsd_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?

 1340in_xml_literal(Type, Val, Val0) :-
 1341    xml_is_dom(Val),
 1342    !,
 1343    write_xml_literal(Type, Val, Val0).
 1344in_xml_literal(xml, Val, Val0) :-
 1345    parse_partial_xml(load_xml, Val, DOM),
 1346    write_xml_literal(xml, DOM, Val0).
 1347in_xml_literal(html, Val, Val0) :-
 1348    parse_partial_xml(load_html, Val, DOM),
 1349    write_xml_literal(html, DOM, Val0).
 1350
 1351parse_partial_xml(Parser, Val, DOM) :-
 1352    setup_call_cleanup(
 1353        new_memory_file(MF),
 1354        (   setup_call_cleanup(
 1355                open_memory_file(MF, write, Out),
 1356                format(Out, "<xml>~w</xml>", [Val]),
 1357                close(Out)),
 1358            setup_call_cleanup(
 1359                open_memory_file(MF, read, In),
 1360                call(Parser, stream(In), [element(xml, _, DOM)], []),
 1361                close(In))
 1362        ),
 1363        free_memory_file(MF)).
 1364
 1365
 1366write_xml_literal(xml, DOM, Text) :-
 1367    with_output_to(atom(Text),
 1368                   xml_write_canonical(current_output, DOM, [])).
 1369write_xml_literal(html, DOM, Text) :-
 1370    with_output_to(atom(Text),
 1371                   html_write(current_output, DOM,
 1372                              [ header(false),
 1373                                layout(false)
 1374                              ])).

 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'.

 1402rdf_canonical_literal(In, Literal) :-
 1403    ground(In),
 1404    !,
 1405    pre_ground_object(In, DBTerm),
 1406    post_object(Literal, DBTerm).
 1407rdf_canonical_literal(In, _) :-
 1408    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

 1421%       For example,
 1422%
 1423%       ==
 1424%       ?- rdf_lexical_form(2.3^^xsd:double, L).
 1425%       L = "2.3E0"^^'http://www.w3.org/2001/XMLSchema#double'.
 1426%       ==
 1427
 1428rdf_lexical_form(Literal, Lexical) :-
 1429    pre_ground_object(Literal, literal(Lit0)),
 1430    !,
 1431    text_of0(Lit0, Lexical).
 1432rdf_lexical_form(Literal, _) :-
 1433    type_error(rdf_literal, Literal).
 1434
 1435text_of0(type(TypeA, LexicalA), LexicalS^^TypeA) :-
 1436    atom_string(LexicalA, LexicalS).
 1437text_of0(lang(LangA, LexicalA), LexicalS@LangA) :-
 1438    atom_string(LexicalA, LexicalS).
 1439
 1440
 1441                 /*******************************
 1442                 *       POST PROCESSING        *
 1443                 *******************************/
 1444
 1445:- rdf_meta
 1446    post_object(o,o),
 1447    out_type(r,-,+). 1448
 1449post_object(Val, _) :-
 1450    ground(Val),
 1451    !.                 % already specified and matched
 1452post_object(URI, URI0) :-
 1453    atom(URI0),
 1454    !,
 1455    URI = URI0.
 1456post_object(Val@Lang, literal(lang(Lang, Val0))) :-
 1457    nonvar(Lang),          % lang(Lang,Text) returns var(Lang) if no 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    !,
 1465    atomic(Plain),
 1466    atom_string(Plain, Val).
 1467post_object(Val@Lang, literal(_, lang(Lang, Val0))) :-
 1468    nonvar(Lang),
 1469    !,
 1470    atom_string(Val0, Val).
 1471post_object(Val^^Type, literal(_, type(Type, Val0))) :-
 1472    !,
 1473    out_type(Type, Val, Val0).
 1474post_object(Val^^xsd:string, literal(_, Plain)) :-
 1475    atomic(Plain),
 1476    atom_string(Plain, Val).
 1477
 1478out_type(xsd:string, Val, Val0) :-     % catches unbound type too
 1479    !,
 1480    atom_string(Val0, Val).
 1481out_type(Type, Val, Val0) :-
 1482    out_type_hook(Type, Val, Val0),
 1483    !.
 1484out_type(IntType, Val, Val0) :-
 1485    xsd_numerical(IntType, _Domain, _BasicType),
 1486    !,
 1487    xsd_number_string(Val, Val0).
 1488out_type(DateTimeType, Val, Val0) :-
 1489    xsd_date_time_type(DateTimeType),
 1490    !,
 1491    out_date_time(DateTimeType, Val, Val0).
 1492out_type(xsd:boolean, Val, Val0) :-
 1493    !,
 1494    Val = Val0.
 1495out_type(rdf:'XMLLiteral', XML, DOM) :-
 1496    xml_is_dom(DOM),
 1497    !,
 1498    with_output_to(string(XML),
 1499                   xml_write(DOM, [header(false)])).
 1500out_type(_Unknown, Val, Val0) :-
 1501    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.

 1509out_date_time(Type, Prolog, Lexical) :-
 1510    catch(xsd_time_string(Prolog, Type, Lexical),
 1511          error(_,_),
 1512          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.

 1522                 /*******************************
 1523                 *          ENUMERATION         *
 1524                 *******************************/

 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.

 1533rdf_term(N) :-
 1534    ground(N),
 1535    !,
 1536    pre_object(N, N0, _, _),
 1537    visible_term(N0).
 1538rdf_term(N) :-
 1539    gen_term(N).
 1540
 1541gen_term(N) :-
 1542    resource(N),
 1543    visible_term(N).
 1544gen_term(O) :-                          % performs double conversion!
 1545    rdf_literal(O),
 1546    (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.

 1554rdf_literal(Term) :-
 1555    ground(Term),
 1556    !,
 1557    (   boolean(Term)
 1558    ;   \+ atom(Term)
 1559    ),
 1560    !,
 1561    pre_ground_object(Term, Object),
 1562    (rdf_db:rdf(_,_,Object)->true).
 1563rdf_literal(Term) :-
 1564    pre_object(Term,literal(Lit0), _, _),
 1565    rdf_db:rdf_current_literal(Lit0),
 1566    (rdf_db:rdf(_,_,literal(Lit0))->true),
 1567    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.

 1574rdf_bnode(BNode) :-
 1575    atom(BNode),
 1576    !,
 1577    current_bnode(BNode).
 1578rdf_bnode(BNode) :-
 1579    rdf_db:rdf_resource(BNode),
 1580    current_bnode(BNode).
 1581
 1582current_bnode(BNode) :-
 1583    rdf_is_bnode(BNode),
 1584    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.

 1591rdf_iri(IRI) :-
 1592    atom(IRI),
 1593    !,
 1594    \+ rdf_is_bnode(IRI),
 1595    visible_term(IRI).
 1596rdf_iri(IRI) :-
 1597    resource(IRI),
 1598    \+ rdf_is_bnode(IRI),
 1599    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.

 1606rdf_name(Name) :-
 1607    atom(Name), \+ boolean(Name),
 1608    !,
 1609    \+ rdf_is_bnode(Name),
 1610    visible_term(Name).
 1611rdf_name(Name) :-
 1612    ground(Name),
 1613    !,
 1614    pre_ground_object(Name, Name0),
 1615    (rdf_db:rdf(_,_,Name0)->true).
 1616rdf_name(Name) :-
 1617    rdf_iri(Name).
 1618rdf_name(Name) :-
 1619    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.

 1634rdf_predicate(P) :-
 1635    atom(P),
 1636    !,
 1637    (rdf(_,P,_) -> true).
 1638rdf_predicate(P) :-
 1639    rdf_db:rdf_current_predicate(P),
 1640    (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.

 1649rdf_object(O) :-
 1650    ground(O),
 1651    !,
 1652    (   atom(O), \+ boolean(O)
 1653    ->  (rdf_db:rdf(_,_,O) -> true)
 1654    ;   rdf_literal(O)
 1655    ).
 1656rdf_object(O) :-
 1657    rdf_db:rdf_resource(O),
 1658    (rdf_db:rdf(_,_,O) -> true).
 1659rdf_object(O) :-
 1660    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.

 1667rdf_node(N) :-
 1668    var(N),
 1669    !,
 1670    gen_node(N).
 1671rdf_node(N) :-
 1672    pre_ground_object(N, N0),
 1673    visible_node(N0).
 1674
 1675gen_node(N) :-
 1676    rdf_db:rdf_resource(N),
 1677    visible_node(N).
 1678gen_node(O) :-                          % performs double conversion!
 1679    rdf_literal(O),
 1680    (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.

 1688resource(R) :-
 1689    var(R),
 1690    !,
 1691    gen_resource(R).
 1692resource(R) :-
 1693    rdf_db:rdf_resource(R),
 1694    !.
 1695resource(R) :-
 1696    rdf_db:rdf_current_predicate(R),
 1697    !.
 1698
 1699gen_resource(R) :-
 1700    rdf_db:rdf_resource(R).
 1701gen_resource(R) :-
 1702    rdf_db:rdf_current_predicate(R),
 1703    \+ rdf_db:rdf_resource(R).
 1704
 1705visible_node(Term) :-
 1706    atom(Term),
 1707    !,
 1708    (   rdf_db:rdf(Term,_,_)
 1709    ;   rdf_db:rdf(_,_,Term)
 1710    ),
 1711    !.
 1712visible_node(Term) :-
 1713    rdf_db:rdf(_,_,Term).
 1714
 1715visible_term(Term) :-
 1716    atom(Term),
 1717    !,
 1718    (   rdf_db:rdf(Term,_,_)
 1719    ;   rdf_db:rdf(_,Term,_)
 1720    ;   rdf_db:rdf(_,_,Term)
 1721    ),
 1722    !.
 1723visible_term(Term) :-
 1724    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.

 1732rdf_create_bnode(BNode) :-
 1733    var(BNode),
 1734    !,
 1735    rdf_db:rdf_bnode(BNode).
 1736rdf_create_bnode(BNode) :-
 1737    uninstantiation_error(BNode).
 1738
 1739
 1740                 /*******************************
 1741                 *         TYPE CHECKING        *
 1742                 *******************************/

 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).

 1757rdf_is_iri(IRI) :-
 1758    atom(IRI),
 1759    \+ 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).

 1787rdf_is_literal(Literal) :-
 1788    literal_form(Literal),
 1789    !,
 1790    ground(Literal).
 1791
 1792literal_form(_@_).
 1793literal_form(_^^_).