Predicate configuration

[malberts]

The list of allowed predicates should be configurable (https://notepad.rhizome.org/wbsg-rdf-extension-workplan-r2#Extension-Concept [4]).

Our initial plan is to have a simple list in LocalSettings. Example:

$wgWikibaseRdfPredicates = [
	'owl:sameAs',
	'owl:SymmetricProperty',
	'rdfs:subClassOf',
	'rdfs:subPropertyOf',
];

What are some use cases around changing this configuration later?
There are two use cases that came up where it's not clear if we need to support them, or if we do, what to expect. Specifically:

1. A predicate is deprecated or removed, but there are existing entities with that predicate:
   • does the mapping become invalid and all instances need to be removed or hidden?
   • does the mapping become readonly, but still visible?
   • is the mapping still editable, but the predicate cannot change?
   • is the mapping still editable and the predicate can be changed to a new value, but it cannot be changed back to the original value?
2. The original predicate was wrong (e.g. typo), but mappings were already created using the wrong value:
   • does this need some kind of migration mechanism?
   • or would this be detected early and therefore require only minimal manual fixing?

[paulduchesne]

Good questions,

(1) I would be inclined to take a more hardline approach, in that a lack of sync between these properties and the declared mappings throws a terminal error (similar to what I have seen with other misconfigured extensions). eg, a user makes a number of mappings with owl:sameAs and then removes it from the LocalSettings list, the wikibase should refuse to load with a message around a mapping predicate used without being declared. I have no idea if this is a practise you would endorse.

(2) A migration mechanism would be good, presumably this would work better as a php script rather than a gui tool. Going back to another discussion, checking that the predicate "exists" (ie it terminates in some web resource) would be useful to prevent typos, but would not help with cases where a wrong legitimate predicate was used. Although maybe a separate "migrate mapping" tool is not required if the API is robust enough to allow bulk updating of many mappings to use a different predicate?