R879 - modelint/shlaer-mellor-metamodel GitHub Wiki

R879 / 1:1c

Single Select yields exactly one Single Instance Flow

Single Instance Flow is yielded by zero or one Single Select

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By definition a Single Select can select at most one instance. A reference to that instance or the empty set flows out of a designated Single Instance Flow.

There are many possible sources for a Single Instance Flow, a Zero One Select being only one. So a given Single Instance Flow may or may not have a Single Select as its source.