customQuery.jdf and its siblings have the following
xmlns:Circus="Circus Schema URI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Query ID="Q1" Type="Circus:IsClownHappy" xsi:type="QueryIsClownHappy">
The value of xsi:type is wrong as it infers the type is from the default i.e. JDF namespace.
At very least it should be
<Query ID="Q1" Type="Circus:IsClownHappy" xsi:type="Circus:QueryIsClownHappy">
I think for the example this is ok - however, I think it presumes that a definition for the type can be found and thus the creator would need to suppy a schema for the Circus. I can't establish if this is precisely the case though, so I'd go with my fix above.