DecisionDefinitionEntity - difference between resourceName and diagramResourceName

just wondering … when I deploy a DmnModelInstance, the resourceName I chose for addModelInstance("my-diagram.dmn", modelInstance) gets set in DecisionDefinitionEntity#resourceName … but as I have multiple decisionTables in my diagram, I would have expected to be the diagramResourceName … what is the difference between those fields? When is diagramResourceName filled? Thanks.