  Wikidata is a knowledge graph increasingly adopted by many communities for
diverse applications. Wikidata statements are annotated with qualifier-value
pairs that are used to depict information, such as the validity context of the
statement, its causality, provenances, etc. Handling the qualifiers in
reasoning is a challenging problem. When defining inference rules (in
particular, rules on ontological properties (x subclass of y, z instance of x,
etc.)), one must consider the qualifiers, as most of them participate in the
semantics of the statements. This poses a complex problem because a) there is a
massive number of qualifiers, and b) the qualifiers of the inferred statement
are often a combination of the qualifiers in the rule condition. In this work,
we propose to address this problem by a) defining a categorization of the
qualifiers b) formalizing the Wikidata model with a many-sorted logical
language; the sorts of this language are the qualifier categories. We couple
this logic with an algebraic specification that provides a means for
effectively handling qualifiers in inference rules. Using Wikidata ontological
properties, we show how to use the MSL and specification to reason on
qualifiers. Finally, we discuss the methodology for practically implementing
the work and present a prototype implementation. The work can be naturally
extended, thanks to the extensibility of the many-sorted algebraic
specification, to cover more qualifiers in the specification, such as uncertain
time, recurring events, geographic locations, and others.

Artificial Intelligence