Hello Novulist, I’m trying to understand the differences between a mandatory consume and an optional consume. Could someone explain how these two types of consumes function and in what scenarios each is typically used? Any examples to clarify the distinctions would also be highly appreciated. Thank you in advance.
In principle, for everything that you consume in a component, there needs to be another component in your application composition that produces it. The exception to that rule are process concepts that are marked optional (i.e. that have the red exclamation mark in your screenshot turned off). If all usages of a consumed process concept in a component revision are marked as optional, then that component revision will register as only optionally consuming that process concept, and the composer will not require you to include a component that produces it.
For a usage of a process concept to be optional, you need to make sure that its return values are either not used, or that you provide a default value for it. The problem visitor will tell you if such default values are missing. If you have provided a default value, and the process concept is not produced in the application composition, then the references to the return values will be replaced by that default value.
When a process concept is marked as optional, it will get an extra implicit return value called is_produced, which is replaced with true or false when the application is integrated.
The most common use of optional process concepts is to allow other components to perform an optional substep in a process, without creating a dependency on a component that implements it. That way, application can be kept as small as possible. For examples, you could look at the public model M3445 - Novulo Verkopen. It contains dozens of optionally consumed process concepts.
On the other hand, if a component cannot function without an implementation for a process concept, mark it as required, and the composer will enforce that a producing component is selected. Novulo Verkopen also contains a couple of required consumed process concepts, one of which is a process for generating new order numbers.
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