"Use of undefined constant SMW_NS_PROPERTY - assumed 'SMW_NS_PROPERTY' in ...LocalSettings.php"

After installing and adding the following lines to the "LocalSettings.php" file

wfLoadExtension( 'SemanticMediaWiki' );
$smwgNamespacesWithSemanticLinks[SMW_NS_PROPERTY] = true;

the following message occurs:

Use of undefined constant SMW_NS_PROPERTY - assumed 'SMW_NS_PROPERTY' in ...LocalSettings.php

This error appears if you do not use enableSemantics() but load SemanticMediaWiki like a regular extension.1 To resolve this, add the following to the LocalSettings.php file:

SMW 4+

wfLoadExtension( 'SemanticMediaWiki' );
enableSemantics( 'example.org' );
$smwgNamespacesWithSemanticLinks[SMW_NS_PROPERTY] = true;

Before SMW 4

enableSemantics( 'example.org' );
$smwgNamespacesWithSemanticLinks[SMW_NS_PROPERTY] = true;

Alternatively, this issue may occur in more recent versions of the software. See issue 5281.