  Wikidata is one of the most successful Semantic Web projects. Its underlying
Wikibase data model departs from RDF with the inclusion of several features
like qualifiers and references, built-in datatypes, etc. Those features are
serialized to RDF for content negotiation, RDF dumps and in the SPARQL
endpoint. Wikidata adopted the entity schemas namespace using the ShEx language
to describe and validate the RDF serialization of Wikidata entities. In this
paper we propose WShEx, a language inspired by ShEx that directly supports the
Wikibase data model and can be used to describe and validate Wikibase entities.
The paper presents a the abstract syntax and semantic of the WShEx language.
