Understanding formal expressions really come down what tool you are using for BPMN. If you are using a tool, there is specific executable language or formal expressions within the standard. For instance an unified expression language (UEL) for a conditional sequence flow from our book (Figure 168), may look like this in XML:
<sequenceFlow is="flow1"
Name="fromEvaluateTrainingMaterialtoModifyVideoResource" sourceRef="EvaluateTrainingMaterial"
targetRef="ModifyVideoResource"
<conditionExpression xsi:type="tFormalExpression">
${evaluationresult == 'update video required'}
</conditionExpression>
</sequenceFlow>
Basically, this expression is indicated that when the condition "update video required" is the result of our evaluation of training material, we move from activity Evaluate Training Material to Modify Video Resource.
For those who are learning or may have experience with formal expressions, share any examples you may have, or feel free to point out how I could better write my formal expression.