How to set value in expression of rule for scheme in orchestration?

I don’t know how to configure the expression of rule of Decide shape.

My code for the expression is:

Message_2.Article.Approved = false;

XML code in scheme Article.xsd:

  <xs:element name="Approved">
  <xs:simpleType>
  <xs:restriction base="xs:boolean" /> 
  </xs:simpleType>
  </xs:element>

The error is if' conditional must have boolean type.

The Message Type of Message2 is BizTalk_Server_Project7.Article.

And I have promoted Approved in Article scheme.

What should I do to make Approved false or true?