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:expression [ a sx:OneOf ;
    sx:min 2 ; sx:max 2 ;
    sx:expressions (
      [ a sx:TripleConstraint ; sx:predicate <http://a.example/p1> ]
      [ a sx:TripleConstraint ; sx:predicate <http://a.example/p2> ]
      [ a sx:TripleConstraint ; sx:predicate <http://a.example/p3> ]
    ) ] ] .