R808 - modelint/shlaer-mellor-metamodel GitHub Wiki

R808 / Generalization

Flow is a Labeled Flow or Unlabeled Flow

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For descriptive purposes or to support a textual action language, it is often helpful to label certain Flows.

In the case of a textual action language, Labels take the form of local variable names where an assignment operation establishes the label.

Here's an example in Scrall:

behind the call arrow = ( cabin low and calling up ) or ( cabin high and calling down )

Here a Scalar Flow from a computation with a boolean result is labeled behind the call arrow.

Not every Flow benefits from a name:

destination heights #= (requested stops + requested floors) ## Floor.(Name >> Floor, Height)

In a nested expression like the one above, there is no need to name the intermediate Flows.