SYSML2_ — Messages cannot have explicit flow connection definitions

As for other flow connection usages, the syntax for a message declaration allows for explicit typing by flow connection definitions. However:

• The constraint checkFlowConnectionDefinitionSpecialization requires that a flow connection definition specialize the base type MessageConnection. MessageConnection has source and target ends that redefines corresponding ends from BinaryConnection and Transfer. So, any flow connection definition must be binary, with exactly two ends, either inherited from or redefining the ends of MessageConnection.
• The constraint checkFlowConnectionUsageSpecialization requires that a message (with no owned end features) specialize the base feature messageConnections, which also has source and target ends that redefine the corresponding ends from MessageConnection, binaryConnections and transfers.
• This means that a message declaration with explicit typing by flow connection definitions inherits ends from both the flow connection definitions and its subsetting of messageConnections. Since a message declaration by definition has no owned end features, this cannot be resolve by redefining the inherited end features. The message declaration therefore results in a flow connection usage with more than two ends, which violates the (KerML) constraint validateConnectorBinarySpecialization.