eyeprolog

RDF 1.2 directional language tags

Will Arabic text still read right to left after reasoning?

A page has a welcome label in Arabic and in English. RDF 1.2 can record not only the language of a string but also its base direction. EyeProlog derives display labels and carries that direction through untouched.

Run it in the playground · Source

The question

Which display labels does the welcome page have, and in which writing direction?

This is one of a family of RDF 1.2 examples. RDF data arrives as rdf(Subject, Predicate, Object, Graph) facts, as produced by rdf-prolog-interchange, and results are printed in the same shape.

The data

rdf(iri('https://example.org/welcome'), iri('https://example.org/label'), literal('مرحبا', lang('ar', rtl)), default_graph).
rdf(iri('https://example.org/welcome'), iri('https://example.org/label'), literal('Welcome', lang('en', ltr)), default_graph).

A directional language tag pairs a language with a base direction: rtl (right to left) for Arabic, ltr (left to right) for English. Without it, an application must guess how to lay out mixed-direction text.

The rule

result_rdf(S, iri('https://example.org/displayLabel'), Label, G) :-
  rdf(S, iri('https://example.org/label'), Label, G).

The rule copies the whole literal term, text and tag together. Because the direction is part of the term, it cannot be dropped by accident.

The answer

eyeprolog examples/rdf12-directional-language.pl

result_rdf(iri('https://example.org/welcome'), iri('https://example.org/displayLabel'), literal('مرحبا', lang(ar, rtl)), default_graph).
result_rdf(iri('https://example.org/welcome'), iri('https://example.org/displayLabel'), literal('Welcome', lang(en, ltr)), default_graph).

Both labels keep their direction.

The reason

step(result_rdf(iri('https://example.org/welcome'), iri('https://example.org/displayLabel'), literal('مرحبا', lang(ar, rtl)), default_graph),
     rule(3),
     ['S' = iri('https://example.org/welcome'),
      'Label' = literal('مرحبا', lang(ar, rtl)),
      'G' = default_graph],
     [rdf(iri('https://example.org/welcome'), iri('https://example.org/label'), literal('مرحبا', lang(ar, rtl)), default_graph)]).

The binding for Label shows the Arabic text and its rtl direction moving from the source triple into the result.

The check

condition('C1', resolution, ok, 4).
condition('C4', coverage, ok, 4).
condition('C7', relevance, ok, 6).
trusted(0).
verdict(checked).

Try it

Restrict the rule to right-to-left labels by matching literal(Text, lang(_, rtl)).
Add a Hebrew label and predict both outputs.
Compare with the other RDF 1.2 decks, such as triple terms and annotations.

Learn more in The Art of EyeProlog, Chapter 9.

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