Adding an assert to a schema object

Add asserts to a DFDL schema object to define tests to ensure that data in the message are well-formed.

Before you begin

Create or open a DFDL schema file. See DFDL schema editor for a description of the DFDL schema editor.


  1. In the Editor view, select the DFDL schema object on which you want to add an assert.
  2. On the Asserts and Discriminators tab of the DFDL Properties area, select Asserts, then click Add assert. If a discriminator is already applied to the object, the Asserts option is disabled, as an object cannot have both an assert and a discriminator applied to it.
  3. Enter your test expression in the Test Condition field, and a human-readable failure message in the Message field.
    Content assistance is available for the Test Condition field; press Ctrl+Space to open the XPath Expression Builder.


Your assert is used when the message model is run.