element exam * id {             
    attribute title             { string }
    attribute date              { string }
    attribute time              { string }
    attribute location          { string }
    attribute free              { boolean }
    attribute published         { boolean }
 
    attribute exercise          { ident [ exists /exercise[.] ]}
 
    element examiner * account  {[ /account[./account]/examiner[..exam/id] ]}
 
    element task * id {         
      attribute maxPoints       { double [ . >= 0 ]}
    }                           
    element grade * id {           
      attribute name            { string } [count(./name, ../grade/name) = 1]
      attribute value           { double }
      attribute minPoints       { double }
    }                           [ {exists ./grade[x], exists ./grade[y], x != y} ./grade[x]/value != ./grade[y]/value ]
                                [ {exists ./grade[x], exists ./grade[y], x != y} ./grade[x]/minPoints != ./grade[y]/minPoints ]
                                [ {exists ./grade[x], exists ./grade[y], ./grade[x]/value < ./grade[y]/value} 
                                  ./grade[x]/minPoints > ./grade[y]/minPoints ]
    element participant * id {  [ count (./id, /account/student/id) = 1 ]
      element result * task {   [ exists ..exam/task[./task] ]
        attribute points        { double [ . >= 0 && . <= ..exam/task[../task]/maxPoints ]}
      }
    }
  }

Results depend on tasks, so deleting them is impossible, if they are still referenced. If this is really necessary, the host language has to use the deleteResult procedures first.

The grades only have to be consistent within themselves, nothing depends on them from the outside.

Changing the values of a grade is a method currently present in the implementation, which can be done by removing the grade and adding it. An additional procedure for this might make sense though.

Currently, the participants are not hardwired to an account, I just changed that fact for the schema. Besides that, participants stand for themselves, so deleting one does not affect anything.

Results depend on tasks and have numeric constraints. The procedures can be (and currently are) associated with the Participant class, rather than the Exam class. Basically this means we now have two actually implicit parameters.

Again, changing the values can be done by adding and removing, which also invokes most of the checks. One could offer a change Method of course, which can actually make sense, as the precondition will be easier.