[Systems Engineering] #7. Understanding MBSE (Model Based Systems Engineering)

In this post, we will try to understanding MBSE (Model Based Systems Engineering).

INCOSE, Systems Engineering Vision 2020 describes MBSE as follows.

“MBSE is a formalized modeling application to support system requirements, design, analysis, verification, and verification activities that begin in the conceptual design phase and continue throughout development and later life cycle phases.”

MBSE stands for model-driven approach in systems engineering. To explain this more simply, it means working in a consistent and systematic way using a tool called ‘model’ throughout the entire process of system development and management. Here, ‘model’ refers to various types of schematics or blueprints that represent the system under development.

The key to MBSE is that this model consistently supports the entire process of system development and plays an important role at every stage. Through this model, developers can understand the system specifications and design more clearly and communicate and collaborate effectively based on this. Additionally, you can save time and money by reusing already developed models in other projects, and it also helps with overall quality management.

Simply put, MBSE is an important methodology that makes the system development process more systematic and efficient. This greatly helps in smooth communication between developers as well as building a better quality system.

It is important to clearly understand the differences between document-based and Model-Based Systems Engineering (MBSE) approaches. Although both approaches perform the same life cycle activities described in the INCOSE Systems Engineering Handbook, the key differences arise in the nature of the deliverables.

  1. Document-based approach:
    • In this method, system requirements specifications (SR), system architecture, and system design specifications are created as separate documents.
    • Created documents are stored in a specific repository and are version controlled.
    • A major limitation of document-based approaches is that completeness and consistency between requirements, design, engineering analysis, and test information are spread across multiple documents, making it difficult to assess.
    • This makes it difficult to understand certain aspects of the system and perform the necessary traceability and change impact assessments.
    • Synchronization issues may arise between system requirements and design and lower-level hardware and software design.
    • These issues can lead to inefficiencies and quality issues during the integration and testing phase, or in worst cases, problems after the system is delivered to the customer.
  2. MBSE Approach:
    • MBSE uses dedicated system modeling tools to create integrated and consistent system models.
    • The model serves as a central repository for design decisions, with all design decisions represented as model elements in a single location within the model.
    • When design changes or errors occur, you only need to modify specific parts of the model, and the modeling tool automatically propagates the changes to all relevant diagrams.
    • This approach eliminates the possibility of inconsistencies between different views of the model, and all output generated from the model remains up-to-date.
    • MBSE provides improved quality and economics. It focuses on preventing defects and centers around a new kind of engineering artifact called a system model.

In conclusion, MBSE enables more efficient and consistent systems engineering compared to document-based approaches. This makes it easier to change designs and correct errors, maintain consistency across aspects of the system, and ultimately save time and money.

Before talking about MBSE in more detail, let’s first talk about what a model is.

  1. What is a model: A model is a simplified or abstract representation of a specific aspect or concept of the real world. It simplifies the complexities of the real world, allowing us to understand, analyze, and predict.
  2. Purpose of a model: The main purpose of a model is to make it easier to understand and explain real-world phenomena or systems. Models can represent real-world complex systems in a simpler form, clarifying the system’s key characteristics or operating principles.
  3. Importance of Abstraction: Models do not contain all the details of the real world. This is an intentional abstraction that removes irrelevant information or unnecessary complexity, allowing you to focus on important characteristics or patterns. For example, an architectural model may show the basic structure and layout of a building but omit installation details such as electrical wiring or pipelines.
  4. Diversity of models: Models can exist in various forms. This may be an abstract mathematical or logical expression, or a more concrete physical prototype. For example, mathematical models can explain complex phenomena with formulas or equations, and physical models can show the operating principles of buildings or machines in three dimensions.
  5. Representation method: Models can be expressed through graphical symbols, graphs, geometric shapes, nodes and arcs, or text such as programming languages. These different representation methods are chosen depending on the content and purpose of the model. SysML, the main topic of this blog, is one of the ways to express system models.

As such, models are powerful tools for simplifying, understanding, and explaining complex realities. Especially in the field of systems engineering, models play an essential role in the design, analysis, and testing of complex systems.

So what does it feel like to model a system? System models are created using modeling tools and include system specifications, design, analysis, and verification information. The main components are: Please note that this blog only covers modeling systems using SysML.

1. Model Elements: The system model consists of model elements that represent requirements, design, test cases, design rationale, etc. According to Systems Modeling Language (SysML), these elements include structure, behavior, parameters, and requirements. (see picture below)

This Picture shows Simplified View of Model Elements with SysML for MBSE, Model Based System Engineering in order to understanding MBSE
Simplified View of Model Elements with SysML for MBSE

2. Model Repository: Model elements are included in the model repository, which allows you to view the system from different perspectives. Multiple intersection relationships between model elements allow you to focus on different aspects of the system.

3. System Design: The main purpose of a system model is to support the assignment of requirements to system components, thereby enabling the design of a system that meets the requirements. The model includes component interconnections and interfaces, interactions, related functions, performance, and physical characteristics.

This picture shows relationships between System Model, Software Model and Hardware Model
Relationships between System Model, Software Model and Hardware Model

4. Requirements Tracking: Text requirements are also captured in the model to enable tracking of system requirements. This promotes consensus between system designers and subsystem and/or component developers.

5. Data Exchange and Documentation Generation: Component developers receive requirements through model data exchange mechanisms or through documentation automatically generated from the model. This also provides information on how the design meets the requirements.

6. System Integration and Traceability: Using a system model provides a mechanism to specify and integrate subsystems and components into the system and maintain traceability between system and component requirements.

7. Engineering Analysis and Simulation: System models can be integrated with engineering analysis and simulation models to perform calculations and dynamic execution. This requires extending the system modeling environment to the execution environment.

In this way, system models play an important role in the overall systems engineering process. Models allow you to effectively manage and coordinate all aspects of a system, from requirements definition to design, verification, and integration. This makes a significant contribution to increasing the efficiency of the design process, reducing errors, and improving the quality and performance of the overall system.

The model elements that make up the system model are stored in a model repository and displayed in diagrams as graphic symbols. These model repositories play a key role in the Model-Based Systems Engineering (MBSE) approach. This allows you to manage the elements of your system model and increase the efficiency and effectiveness of your systems engineering process. The main functions and features of the model repository can be summarized as follows:

  1. Storage and management of model elements: The model repository stores all model elements that make up the system model. These elements are represented visually through diagrams and can be created, modified, and deleted using modeling tools.
  2. Input and retrieval of model information: The modeler uses the symbols on the diagram to input model information into the model repository and retrieves the model information from the repository. Specification, design, analysis, and validation information previously captured in documentation is now included in the model repository.
  3. Visual representation of the model: The model can be viewed through diagrams, tables, or reports generated by querying the model repository. This allows you to understand and analyze various aspects of your system model.
  4. Automated Document Generation: Many modeling tools have the ability to automatically generate system specifications and design documentation, saving you time and money.
  5. Traceability between elements: Model elements corresponding to requirements, design, analysis, and verification information may appear in various diagrams, but the relationships between them allow them to be traced to each other.
  6. Constraints in the modeling language: The modeling language limits the types of relationships that can exist in the model, and enforces these constraints through model checker routines.
  7. Integrated Framework for Systems Engineering: Systems models provide a framework that integrates models from various specialized engineering disciplines, including hardware, software, test, reliability, safety, and security.

These model repository capabilities strengthen the overall systems engineering process by integrating all aspects of the system and improving the quality of traceability and impact assessment. Compared to document-based approaches, model-based approaches significantly improve the accuracy and accessibility of information and are more effective in managing the complexity of systems engineering.

In fact, models and associated diagramming techniques have long been an important part of document-based systems engineering. Examples include block diagrams, sequence diagrams, state machines, and Simulink, which have recently become important in the electronics industry. However, these tools are primarily focused on supporting specific aspects of analysis or design. The transition to MBSE means moving the control of these systems from document to model-based. MBSE integrates system requirements, design, analysis, and verification models to handle them in a more cohesive manner.

In this post, we briefly looked at MBSE and models. Since the post is getting longer, I will discuss MBSE in more detail in the next post

[Systems Engineering] #1. INTRODUCTION – Navigating Systems Engineering

[Systems Engineering] #2. Definition of System

[Systems Engineering] #3. Understanding Systems Thinking

[Systems Engineering] #4. Useful knowledge of systems thinking

[Systems Engineering] #5. Understanding Systems engineering

[Systems Engineering] #6. Who is Systems Engineer

[Systems Engineering] #7. Understanding MBSE (Model Based Systems Engineering)

[Systems Engineering] #8. Additional practical knowledge about MBSE

[Systems Engineering] #9. What is Good System Model?

[Systems Engineering] #10. Understanding SysML (System Modeling Language)

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