Broadcast date: December 4th, 2021

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Welcome to the 4th door of our MBSE Podcast Advent Calendar. Behind the door, we take a look at base architectures. 

We already mentioned the base architecture in the previous days. Now, let’s talk about what it is.

In systems engineering, we distinguish the problem space and the solution space. For example, the requirements are in the problem space and are solution-free, and the system architecture is in the solution space and satisfies the requirements.

Sounds simple, but it’s not. What does it mean that requirements are solution-free? What is a solution? Can a requirement request that a vehicle has four wheels? Or is wheel already a solution?

The separation of problem and solution space is correct. What is missing is the consideration that there are several levels of it. A solution space on one level is the basis for the problem space on the next level.

To return to the vehicle example: On one level we have requirements in the problem space that the system should be able to move on roads. In the solution space, we have chosen the concept of wheel, as one alternative, in the architecture to satisfy these requirements. 

This architecture is the basis for the next level. The wheel is assumed and we now set the requirement that there should be 4 wheels with the size and so on.

The system architecture from the higher-level solution space, we call base architecture. When we describe them explicitly, we more strongly separate the problem space from the solution space and make implicit assumptions explicit. The decisions in the base architecture are constraint requirements for the next level.

The basic architecture of our Christmas tree already specifies a lot, since the basic structure of a Christmas tree is fixed and not part of the solution space. The diagram shows the definition of the elements in a block definition diagram. Our “The MBSE Podcast Christmas Tree” – abbreviated TMPCT – Base Architecture includes a transportation net, a tree with a trunk and branches, a Christmas tree star, fairy lights, a stand, and a transportation package. SysML modeling tools allow us to use images instead of the SysML shapes. This makes it more illustrative.

TMPCT Base Architecture Definition

The base architecture also leads to a base system context, which we define in the following block definition diagram. External actors are the floor in a room, Santa Claus, the owner of the tree, eventually children, a power supply, the planet environment for sustainability considerations, and the TMPCT Base Architecture itself.

TMPCT Base Arcitecture Context Definition

Depicted in an internal block diagram shows the typical figure of a system context diagram. Here, comes the context of our base architecture:

TMPCT Base Architecture including Context

We leave out most of the connections inside our Christmas tree. They will be defined later in the physical architecture of our system. When we look at those, we also see how the relationship to the base architecture can be modeled. We will explain the concept of Ports, connectors, and part properties in later sessions. 

When we consider the system context, we will cover how the system context is related to the base architecture context.

What was the surprise behind this door? It is the basic architecture itself that is special. It’s always there, but it’s often carelessly documented. The blurring between problem space and solution space, as well as the implicit assumptions, leads to many potential problems in projects.

So much for the fourth door of our MBSE Podcast Advent Calendar. We wish you a great 4th of December.

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