R55

R55 / 1c:Mc-1

Process Input Port consumes zero or one External Input

External Input feeds zero, one or many Process Input Port

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An External Input cannot directly feed a Store and it cannot simply pass its data across to an External Output. If an External Input is used, it must be used by a Process Input Port.

Consider the example of a state activity from the Shlaer-Mellor metamodel example. An event on a transition my provide a number of input parameters to the activity. Each of these would be manifested as an External Input on a data flow Graph. But there is no requirement that a provided input parameter actually be used anywhere within the activity. Based on this example, at least, it seems reasonable to allow Internal Inputs to be selectively ignored.

Formalization

External Process Input.(Process input port, Process, Graph) ->
    Process Input Port.(Name, Process, Graph)
External Process Input.(External input, Graph) ->
    External Input.(Name, Graph)