KERML11 — Special metaclasses supporting Flow shorthand

The shorthand textual notation for a flow:

flow F of p : P from a.output to b.input;

is parsed to an abstract syntax representation using the special metaclasses PayloadFeature and FlowEnd. However, these metaclasses are not used in the longhand notation:

flow f {
    feature p : P redefines payload;
    end references a {
        ref output redefines sourceOutput;
    }
    end references b {
        ref input redefines targetInput;
    }
}

Further, the derived properties deriveFlowFlowEnd, deriveFlowPayloadFeature and deriveFlowPayloadType will all be empty for the longhand model, because they depend on the special metaclasses as syntactic markers. Finally, the abstract syntax does not prevent using the special metaclasses for some but no all parts of a flow (e.g., the flow has a PayloadFeature, but the ends are not FlowEnds), which cannot be represented in the textual notation at all.