Broadcast date: December 6th, 2021

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Welcome to the 6th door of our MBSE Podcast Advent Calendar. Behind the door, we take a look at the system use cases. 

There are a lot of methods for modeling use cases published in many books, papers, and other publications.

We present a very simple method and avoid use case relationships such as include, extend, or generalization between use cases.

The use cases here are simply a list of the functions of the system in which actors are involved and which create value for an actor or stakeholder. Let’s look at it in our model.

TMPCT System Use Cases

Some of our use cases are depicted in the use case diagram with the associated actors. 

There are a few special features in the modeling:

  • The actor Carrier of the use case “Transport Christmas tree” is a generalization of the actors “Christmas Tree Seller” and “Owner”. It is an XOR condition. The use case has only one actor which could be either a seller or an owner.
  • The association end at the Child actor has a multiplicity 0..*, which means that children are optional, but there could be many of them who are enjoying the Christmas tree.

Although use case diagrams are very common, they just show more or less only a graphical list of use cases. You can depict the same information in a table plus more properties.

TMPCT System Use Cases in a Table

The table also shows the documentation of the use case as well as additional properties introduced by the SYSMOD stereotype “systemUseCase” for the trigger and the result of the use case. The triggerSignal property stores a signal to formalize the trigger. You will meet it again when we talk about state machines.

That’s the learning surprise behind this door. Tables are valid views of SysML model elements, and they can be much more convenient than the diagram. You do not have layout effort, and – depending on the tool – tables are, typically, queries and always up-to-date. Use the tables for the daily engineering work, and diagrams for workshops, presentations, or eventually documents.

So much for the sixth door of our MBSE Podcast Advent Calendar. We wish you a great 6th of December.

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