owl:versionInfo with a language code causes PHP warnings

[akeldamas]

URL address of the page where you encountered the problem

No public URL is available. I identified the problem on a fresh local Skosmos v3.4 container instance.

Description of the problem

While creating a fresh thesaurus using OWL, I noticed that adding a language code to owl:versionInfo causes PHP warnings.

Steps to reproduce

1. Load a vocabulary containing:

@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix skos: <http://www.w3.org/2004/02/skos/core#> .

<https://example.org/thesaurus> a owl:Ontology, skos:ConceptScheme;
    skos:prefLabel "Test thesaurus"@en;
    owl:versionInfo "5"@en .

2. Open the vocabulary page.

The page displays:

Warning: Undefined array key 0 in /var/www/html/src/model/Vocabulary.php on line 225

Deprecated: explode(): Passing null to parameter #2 ($string) of type string is deprecated in /var/www/html/src/model/Vocabulary.php on line 326

Expected outcome

The version information displays without PHP warnings.

Additional information (e.g. screenshots) about the problem

Tested with Skosmos container using v3.4 and PHP 8.3.

Tracing the issue shows that Skosmos stores the literal value as its array key:

Skosmos/src/model/Vocabulary.php

Line 196 in b0367e2

$ret[$prop][$val->getValue()] = $val;

In the example I showed it would create [5 => $val], but the code later assumes that it is stored as key 0:

Skosmos/src/model/Vocabulary.php

Lines 224 to 226 in b0367e2

	if (isset($ret['owl:versionInfo'])) { // if version info available for vocabulary convert it to a more readable format
	$ret['owl:versionInfo'][0] = $this->parseVersionInfo($ret['owl:versionInfo'][0]);
	}

OWL supports literal values on annotation properties. So while little value might be gained from a language code it still is valid OWL.

The browser you used when the problem appeared

Not browser-specific. The same warnings are reproducible using curl.