rdf_portray.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2009-2020, University of Amsterdam
                              VU University Amsterdam
                              CWI, Amsterdam
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*/

:- module(rdf_portray,
          [ rdf_portray_as/1,           % +Style
            rdf_portray_lang/1          % +Lang
          ]).
:- use_module(library(semweb/rdf_db),[rdf_global_id/2,rdf_has/3]).
:- use_module(library(semweb/rdfs),[rdfs_ns_label/2]).

:- autoload(library(error),[must_be/2]).
:- autoload(library(lists),[member/2]).

/** <module> Portray RDF resources

This module defines  rules  for  user:portray/1   to  help  tracing  and
debugging  RDF  resources  by  printing   them    in   a   more  concise
representation and optionally adding comment  from   the  label field to
help the user interpreting the URL. The main predicates are:

        * rdf_portray_as/1 defines the overall style
        * rdf_portray_lang/1 selects languages for extracting label comments

@tbd    Define alternate predicate to use for providing a comment
@tbd    Use rdf:type if there is no meaningful label?
@tbd    Smarter guess whether or not the local identifier might be
        meaningful to the user without a comment.  I.e. does it look
        `word-like'?
*/

:- dynamic
    style/1,
    lang/1.

%!  rdf_portray_as(+Style) is det.
%
%   Set the style used to portray resources.  Style is one of:
%
%           $ =|prefix:id|= :
%           Write as NS:ID, compatible with what can be handed to
%           the rdf predicates.  This is the default.
%
%           $ =writeq= :
%           Use quoted write of the full resource.
%
%           $ =|prefix:label|= :
%           Write namespace followed by the label.  This format
%           cannot be handed to rdf/3 and friends, but can be
%           useful if resource-names are meaningless identifiers.
%
%           $ =|prefix:id=label|= :
%           This combines prefix:id with prefix:label, providing both human
%           readable output and output that can be pasted into the
%           commandline.

rdf_portray_as(Style) :-
    must_be(oneof([writeq, prefix:id, prefix:label, prefix:id=label]), Style),
    retractall(style(_)),
    assert(style(Style)).

%!  rdf_portray_lang(+Lang) is det.
%
%   If Lang is a list, set the list or preferred languages. If it is
%   a  single  atom,  push  this  language  as  the  most  preferred
%   language.

rdf_portray_lang(Lang) :-
    (   is_list(Lang)
    ->  must_be(list(atom), Lang),
        retractall(lang(_)),
        forall(member(L,Lang), assert(lang(L)))
    ;   must_be(atom, Lang),
        asserta(lang(Lang))
    ).

try_lang(L) :- lang(L).
try_lang(_).


:- multifile
    user:portray/1.

user:portray(URL) :-
    atom(URL),
    http_url(URL),
    !,
    (   style(Style)
    ->  true
    ;   Style = prefix:id
    ),
    portray_url(Style, URL).
user:portray(URL) :-
    atom(URL),
    atom_concat('_:file://', URL2, URL),
    sub_atom(URL2, S, _, A, #),
    sub_atom(URL2, _, A, 0, Local),
    sub_atom(URL2, 0, S, _, Path),
    file_base_name(Path, Base),
    format('_:~w#~w', [Base, Local]).

http_url(URL) :- sub_atom(URL, 0, _, _, 'http://'), !.
http_url(URL) :- sub_atom(URL, 0, _, _, 'https://'), !.

portray_url(writeq, URL) :-
    writeq(URL).
portray_url(prefix:id, URL) :-
    (   rdf_global_id(NS:Id, URL)
    ->  writeq(NS:Id)
    ;   writeq(URL)
    ).
portray_url(prefix:id=label, URL) :-
    (   rdf_global_id(NS:Id, URL)
    ->  Value = NS:Id
    ;   Value = URL
    ),
    (   Id \== '',
        (   (   try_lang(Lang),
                rdf_has(URL, rdfs:label, literal(lang(Lang, Label)))
            ->  nonvar(Lang),
                \+ label_is_id(Label, Id)
            )
        ->  format('~q/*"~w"@~w*/', [Value, Label, Lang])
        ;   rdf_has(URL, rdfs:label, literal(type(Type, Label))),
            nonvar(Type),
            \+ label_is_id(Label, Id)
        ->  (   rdf_global_id(TNS:TId, Type)
            ->      TVal = TNS:TId
            ;       TVal = Type
            ),
            format('~q/*"~w"^^~w*/', [Value, Label, TVal])
        ;   rdf_has(URL, rdfs:label, literal(Label)),
            atom(Label),
            Label \== Id
        ->  format('~q/*"~w"*/', [Value, Label])
        )
    ->  true
    ;   writeq(Value)
    ).
portray_url(prefix:label, URL) :-
    rdfs_ns_label(URL, Label),
    write(Label).

label_is_id(_, Var) :-
    var(Var), !, fail.
label_is_id(Label, Label) :- !.
label_is_id(L0, L1) :-
    downcase_atom(L0, Lwr),
    downcase_atom(L1, Lwr).