Model-Based Systems Engineering | MBSE

Edited from: https://modelbaba.com/mbse/101.html

1. What is a system

A system is a whole composed of interrelated elements or parts. It is precisely because of the correlation between the constituent elements that when they are combined, new features usually emerge at the system level, such as the emergence of new functions, the enhancement of existing functions, etc. This feature is called the system's emergent.

To fully define a system, it is generally carried out from two perspectives: the structural characteristics and behavioral characteristics of the system. The structural characteristics of the system include: composition structure, interface, performance index, physical characteristics, etc. The behavioral characteristics of the system include: system functions, messages sent and received, status, etc.

2. What is systems engineering

With the continuous development and application of science and technology, real systems are becoming more and more complex, such as military aircraft, aircraft carriers, mobile phones, distributed information systems, etc. In particular, the relationship between the system or system components is becoming more and more complex, which brings great challenges to the design and development of the system. How to deal with this complexity and design a system that meets people's growing needs and has a competitive advantage in the market has become an urgent problem for engineers to solve!

After continuous practice and exploration, Systems Engineering (SE) has gradually been widely accepted in aviation, defense and other industrial fields. Systems engineering is a branch of systems science, actually the practical application of systems science. It can be used in all aspects with large systems, including human society, ecological environment, natural phenomena, organizational management, etc., such as environmental pollution, population growth, traffic accidents, arms races, chemical processes, information networks, etc. Systems engineering is a theory and method that takes large-scale complex systems as the research object, designs, develops, manages and controls them according to a certain purpose, in order to achieve the best overall effect. All in all, systems engineering is an interdisciplinary comprehensive approach, which emphasizes the use of system principles and concepts, as well as scientific, technical and management methods to achieve system design and development.

Systems engineering focuses on the following areas:

• 1) Establish, balance, and integrate stakeholder objectives and define actual or anticipated customer needs, concepts of operation, and desired functionality at the beginning of development;
• 2) Establish an appropriate life cycle model, process approach and wall calendar structure, taking into account the level of complexity, uncertainty, possible change and diversity;
• 3) generate and evaluate concepts and architectures for alternative solutions;
• 4) Baselines and requirements for each phase and selected solution architecture;
• 5) Perform design synthesis, system verification and validation;
• 6) Consider the problem and solution holistically, consider the necessary supporting systems and services, identify the role that parts and their relationships play in the overall behavior and performance of the system, and determine how to balance all factors to achieve satisfactory results.

The typical process of system development using the idea of ​​system engineering is shown in the figure below.

SE Typical V Process

3. What is model-based systems engineering

Traditionally, when people use the SE process for system design, they focus on documents. The work results of each stage are based on documents, and the interaction between different teams is also based on documents. However, with the increasing complexity of the system, this document-centric system engineering (Text Based Systems Engineering, TBSE) method has exposed many defects, such as the inability to guarantee the consistency of information, the difficulty of changing, and the difficulty of describing activities. In order to solve the problems existing in the traditional document-based systems engineering, the International Society of Systems Engineering (INCOSE) proposed a model-based systems engineering (Model Based Systems Engineering, MBSE) method. With the model as the core, MBSE has the advantages of unambiguous knowledge expression, reusability, and system design integration. It can solve the challenges brought by traditional document-based system engineering with the increase of system complexity.

Definition of MBSE: MBSE is the formalized application of modeling (activity) to support activities such as system requirements, design, analysis, verification, and validation, starting at the conceptual design stage and continuing through to design Development and all subsequent life cycle phases.

Aiming at the problems existing in complex system engineering, MBSE uses the advantages of computing technology, network technology, storage capacity, and information technology to transform system engineering from the original document-centered to model-centered, overcoming a large number of documents and materials in the past, Non-quantitative, non-standard, and difficult-to-verify working methods guided by experience such as specification descriptions, operation manuals, and interface descriptions. By establishing digital, precise, and standardized basic models and business models, the advantages of the integrated model are used to support the system. The completion of a series of activities such as analysis, design, optimization, planning, and evaluation of the engineering process, and support for feedback and verification between various activities.

4, MBSE elements

As shown in the figure below, MBSE consists of three elements.

3 elements of MBSE

• 1) MBSE Modeling Language
• The modeling language defines various visual elements in the modeling process and the semantics represented by various elements. The language used in MBSE mainly refers to SysML .
• 2) MBSE modeling tool
• MBSE modeling tools refer to software systems used by system developers in the process of creating and managing models. Modeling tools can deploy one or several modeling languages ​​to provide visualization functions for various elements in the modeling language, and give various elements semantics according to the standards of the modeling language.
• 3) MBSE methodology
• The MBSE methodology defines how the design team uses various graphics of the system modeling language to build a system model, that is, the workflow. At present, the main methods include: Harmony SE proposed by IBM, Object-Oriented Systems Engineering Method (OOSEM) of INCOSE , Object-Process Methodology (OPM) proposed by Dori , system engineering methodology of Vitech , State Analysis method of Jet Propulsion Laboratory , the MagiGrid methodology proposed by No Magic (now acquired by Dassault) , the Arcadia methodology proposed by Thales, and so on.

5. Advantages of MBSE over TBSE

MBSE uses a model that is easier to understand and understand as the main tool, especially the visual model, which helps designers focus on work related to business logic without too much consideration of specific implementation details related to the platform . In the face of different application fields, MBSE emphasizes the use of powerful and flexible domain-related modeling language to create system models, based on domain knowledge to achieve good communication among different personnel such as domain experts, designers, system engineers, and architects.

Specifically, MBSE has the following advantages over TSE:

• 1) It can clearly describe the initial structure, function and behavior of complex systems and other requirements without ambiguity
• In the traditional system engineering work process, the initial requirements of the system are obtained mainly in the form of documents, but the text description has semantic ambiguity and differences in understanding. Inaccurate requirements description in the initial requirements stage will lead to system design or Huge deviations occur during the realization phase, and such deviations often result in huge financial and time losses.
• 2) Integration of system design.
• Since the establishment of the system model covers the entire life cycle process of the system, including activities such as system requirements, design, analysis, verification and confirmation, it is a unified and overall process that can provide a complete, consistent and traceable system Design, so as to ensure the integration of system design, avoid design conflicts between various components, and reduce risks.
• 3) Enhance knowledge acquisition and reuse.
• The system life cycle includes a lot of information transfer and conversion process, such as the designer needs to extract the demand information generated by the demand analyst to design the system. Due to the modular characteristics of the model, the acquisition, transformation and reuse of information are more convenient and effective.
• 4) The model is reusable and improves work efficiency.
• Compared with the traditional document-centered system engineering design scheme, the model-based system design has stronger modular characteristics, especially in the "object-oriented system design", the coupling between models at the same level is low and the encapsulation is good. Therefore, the later results of the model can be reused or modified for reuse in future research in related fields.
• 5) The model-based system design method can better support the tracking and management of requirements.
• Verifying whether the system design scheme meets the different needs of various users is a very important part of the system engineering process. The model-based system engineering method can establish a mapping relationship matrix between requirements, functions, and systems to track and manage system requirements. The designer can confirm the difference between the plan and the expected result according to the relationship matrix, clarify unfulfilled requirements, and analyze the impact of changes in requirements, functions, and system structure design on the overall system.

6. Summary

Compared with the traditional document-centered system development process, MBSE has brought fundamental changes and improvements to system development from the three dimensions of language, tools and methodology, and can well cope with the increasingly complex models today. challenge. In particular, my country's engineering field is in the process of changing from big to strong, and it is necessary to pay more attention to the disruptive technology of MBSE, such as system engineering, to do a solid job in the research of the basic principles of MBSE, modeling ideas, and workflow, and actively Carry out pilot applications of related models to lay a solid methodological foundation and tool foundation for the development and construction of national defense and civil engineering.