MDMI_ — Properly handling MessageElementRelationships

The current MessageElementRelationship class does not seem to handle message relationships properly, especially given the potential for a MessageElement to have multiple instances, i.e., how does one distinguish between relationships to an instance and relationships to a class.

To handle correctly SemanticElementRelationships, two changes will be introduced.
1. In the SemanticElement class, an association will be added to declare explicitly a parent/child relationship, as defined in a message format.
2. Second, in the SemanticElementRelationship class the Boolean attributes sourceIsInstance and targetIsInstance will be added. If the source SemanticElement has multiple instances then:
· when the sourceIsInstance is true, the defined relationship is for each Instance of the source SemanticElement
· when the sourceIsInstance is false, the defined relationship is for the SemanticElement class as a whole
· when the targetIsInstance is true, the defined relationship is for each Instance of the target SemanticElement
· when the targetIsInstance is false, the defined relationship is for the SemanticElement class as a whole
There are also two additional attributes that are there to help a runtime parse a message. These are minOccurs, which says how many instances of the target at a minimum must be involved in the relationship; and maxOccurs\, which says how many instances at most can be involved in the relationship.