A question about Data Object associated with a Sequence Flow

[Jin Liu]

Hello, 

I found this in BPMN2.0 (11-01-03.pdf): 

"Alternatively, Data Objects MAY be directly associated with a Sequence Flow connector  to represent the same input/output relationships. This is a visual short cut that normalizes two Data Associations: one from an item-aware element (e.g., an Activity) contained by the source of the Sequence Flow, connecting to the Data Object; and the other from the Data Object connecting to a item-aware element contained by the target of the Sequence Flow."

And at Diagram Interchange section about BPMNEdge for DataAssociation, it says "The targetElement of the BPMNEdge is itself of type BPMNEdge where bpmnElement is of type SequenceFlow".

But I have several questions: 

1. Although we can guess the sourceElement as SequenceFlow, what's the bpmnElement of this BPMNEdge? It seems that the BPMNEdge don't allow a empty bpmnElement.

2. I used Trisotech BPMN2.0 modeler for visio Version 3.1 to do this, but when I convert from visio to BPMN2.0, and then convert back to visio file, the edge is missing, is it a bug?

3. The DataAssociation is a concrete class, can I use it directly? But I didn't find a correct method for saving the DataAssociation objects.

Thanks.