PREFIX ex: <http://a.example>
PREFIX sx: <http://www.w3.org/ns/shex#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

[] a sx:Schema ;
    sx:shapes (<http://a.example/S1>) .

<http://a.example/S1> a sx:ShapeDecl ; sx:shapeExpr [ a sx:Shape ;
  sx:extra <http://a.example/p1> ;
  sx:expression
    [ a sx:TripleConstraint ;
      sx:predicate <http://a.example/p1> ;
      sx:valueExpr
        [ a sx:NodeConstraint ;
          sx:values ( <http://a.example/o1> ) ] ] ] .