MBSE

Motivation for System Engineering

Whether it is an advanced military aircraft, a hybrid vehicle, a cell phone, or a distributed information system, today’s systems are expected to perform at levels that were unimaginable a generation ago. Competitive pressures demand that these systems utilize technological advancements to provide continually increasing capabilities at lower costs and within shorter delivery cycles. The enhanced capability often necessitates increased functionality, interoperability, performance, and reliability, frequently within smaller and smaller devices.

The interconnectivity among systems also imposes greater demands on them. Systems can no longer be treated as isolated entities. They function as part of a larger whole that includes other systems, devices, and humans. This interconnected system of systems (SoS) is dynamic, evolving over time as systems are added or removed and as their uses change. These changes lead to evolving requirements for the constituent systems that may not have been anticipated during their initial development. For example, a mobile device that originally provided e-mail communication has evolved to offer Internet functionality, including access to video, global positioning services, and social media. Systems like automobiles, airplanes, and financial systems are also continuously subject to changing requirements, particularly as they become more interconnected.

Systems engineering is a widely accepted approach in the aerospace and defense industries for providing solutions to technologically challenging and mission-critical problems. These solutions often encompass hardware and equipment, software, data, people, and facilities. The potential value of systems engineering for managing complexity and risk and for improving productivity and quality is increasingly being recognized and accepted in other industries, such as automotive, telecommunications, and medical equipment, among others.

A system comprises a set of elements that interact with one another and can be viewed as a whole interacting with its external environment to achieve a specific objective. Systems engineering is a multidisciplinary approach to developing balanced solutions in response to diverse stakeholder needs.

This approach includes both management and technical processes to achieve this balance and mitigate risks that could impact the project’s success. The systems engineering management process aims to ensure that development cost, schedule, and technical performance objectives are met. Typical management activities involve planning the technical effort, monitoring technical performance, managing risk, and controlling the system’s technical baseline.

The technical processes in systems engineering are used to analyse, specify, design, and verify the system to ensure all components work together to achieve the overall objectives. The practice of systems engineering is dynamic and evolves to address the increasing demands previously mentioned.

The System Specification and Design process includes the following activities to provide a balanced system solution that addresses the diverse stakeholders’ needs:

• Elicit and analyse stakeholder needs to understand the problem to be solved, the goals the system is intended to support, and the effectiveness measures needed to evaluate how well the system supports these goals and satisfies the stakeholder needs.

• Specify the required system functionality, interfaces, physical and performance characteristics, and other quality characteristics to support the goals and effectiveness measures.

• Synthesize alternative system solutions by partitioning the system design into components that can satisfy the system requirements.

• Perform analysis to evaluate and select a preferred system solution that satisfies the system requirements and maximizes the effectiveness measures.

• Maintain traceability from the system goals to the system and component requirements and verification results to ensure that requirements and stakeholder needs are addressed.

Model-Based System engineering approach

Projects have traditionally employed a document-based systems engineering approach to carry out system engineering activities. This method involves creating textual specifications and design documents, either in hard copy or electronic formats, which are then shared among customers, users, developers, and testers. System requirements and design information are conveyed through these documents using text descriptions, graphical representations generated with drawing tools, and tabular data and plots derived from analysis models or databases. A document-based systems engineering approach focuses on managing the documentation, ensuring its validity, completeness, and consistency, and verifying that the developed system aligns with the documented specifications.

The document-based approach can be thorough but has some inherent limitations. Assessing the completeness, consistency, and relationships between requirements, design, engineering analysis, and test information is challenging because the information is dispersed across multiple documents. This makes understanding specific aspects of the system and performing traceability and change impact assessments difficult. Consequently, there can be poor synchronization between requirements, system-level design, and lower-level detailed designs, such as software, electrical, and mechanical design.

Furthermore, it complicates the maintenance or reuse of system requirements and design information for evolving or variant system designs. Additionally, the progress of the systems engineering effort is gauged by the status of the documentation, which is hard to maintain and does not accurately reflect the quality of the system requirements and design. These limitations can lead to inefficiencies that affect cost and schedule and can result in quality issues that often emerge during integration and testing, or worse, after the system has been delivered to the customer.

A model-based approach has long been standard practice in fields like electrical and mechanical design. In the 1980s, mechanical engineering shifted from traditional drawing boards to advanced two-dimensional and then three-dimensional computer-aided design tools. Similarly, electrical engineering moved from manual circuit design to automated schematic capture and circuit analysis around the same time. Computer-aided software engineering also gained traction in the 1980s, utilizing graphic models to represent software at abstraction levels above the programming language. Since the introduction of the Unified Modelling Language in the 1990s, modelling for software development has become increasingly popular.

Now, the model-based approach is gaining traction in systems engineering. Advances in computer processing, storage, and network technology, combined with a growing emphasis on systems engineering standards, have created an opportunity to significantly enhance MBSE practices. It is anticipated that MBSE will become as standard in systems engineering as it has in other engineering disciplines and will be fully integrated into a broader model-based engineering framework.

Model-based systems engineering (MBSE) uses systems modelling within the systems engineering process, to support the analysis, specification, design, and verification of the system under development. The main outcome of MBSE is a comprehensive model of the system being developed. This methodology improves the quality of specifications and design, facilitates the reuse of system specifications and design artefacts, and enhances communication among the development team.

Model-Based System Engineering (MBSE) is the formalized application of modelling to support system requirements, design, analysis, verification and validation activities beginning in the conceptual design phase and continuing throughout development and later life cycle phases. MBSE with Arcadia method provides a guided step-by-step to all that are looking to develop systems that meet stakeholder needs aiming at reducing cost and risk.

Value of a model

The system model is generally created using a modelling tool and stored in a model repository. The system model includes system specifications, design, analysis, and verification information. The model consists of model elements that represent requirements, design, test cases, design rationale, and their interrelationships.

The system model defines the components of the system, with the component specifications used as inputs for procuring or designing each component. Component design models can be represented using domain-specific modelling languages, such as UML for software design, or through computer-aided design and computer-aided engineering (CAD/CAE) models for hardware design.

A model helps to understand the growing systems complexity by breaking down systems into simpler constructs that can be understood.

Tackle the lack of understanding of the initial needs not fully analysed in different contexts.

Removes communication problems by using of a common language (i.e., modelling language) to address communication problems, across spoken language barriers and backgrounds.

Encourages and improves interaction with project stakeholders and all engineering disciplines.

Improves quality as it implements:

• Rigorous requirements traceability.

• Facilitates the system design integrity; enhanced design changes detection and update across different areas.

• Improved requirements specification and allocation to subsystems.

• Early identification of requirements issues.

• Consistent documentation, both within and across projects.

Ability to detect defects earlier in the system development cycle with:

• On-going requirements validation through design verification and the use of simulation and automatic verification, increases confidence, reduces risk and costs.

• Helps to verify the system correctness (e.g., interfaces captured and defined, data flow type is correct).

• Helps to verify system completeness (e.g., all modes and states identified and defined), consistency and correctness with fewer changes.

Improves productivity:

• Reuse of existing models to support design and technology evolution.

• Automated generation of documentation.

A model can be defined as a simplified representation of a real system (i.e., product or service).

Different types of models

Different types of models (not extensive list) ca be defined:Mathematical models, which allow reasoning about the System to be performed. It can represent equations.Physical models, such as mock-ups, which provide a picture of what a final system may look like.Visual model, such as drawings and plans.MBSE models, capture the architecture design definition of a system, for example an In-flight entertainment system.How the MBSE model can increase the quality of System design?An MBSE model provides (not extensive list):Visualization: MBSE provides visual models that represent the system’s structure, behaviour, and interactions, making it easier for stakeholders to understand and discuss the design.Common Language: It offers a standardized way to describe the system, which helps bridge the gap between different disciplines, such as engineering, software development, and business analysis. From concept to final design.Interface Definition: MBSE clearly defines the interfaces and interactions between system components, which helps in integrating different subsystems and ensures they work together seamlessly.Risk Identification: By providing a detailed view of the system and its interactions, MBSE helps identify potential risks and vulnerabilities early in the design process.Scenario Analysis: It allows for the analysis of different scenarios, including worst-case situations, to prepare mitigation strategies.Different Perspectives: Independent views allow the system to be represented from multiple perspectives, such as structural, behavioural, functional, and physical views. This multi-faceted approach ensures that all aspects of the system are considered and accurately represented.Targeted Communication: Different stakeholders (engineers, managers, clients) often need different information. Independent views allow for the presentation of relevant details tailored to specific stakeholder needs, facilitating clearer and more effective communication. Focus on Relevant Concerns: Each view can highlight particular concerns, such as security, performance, or usability, enabling stakeholders to focus on the areas most pertinent to their roles. By addressing all the above, a model reduces complexity, facilitates communication and reduces lake of understanding. That drives to increase system design quality, hence: Reduce costs. Reduce time to market Reduce the amount of rework and fixes

MBSE Model

Mathematical Model

Physical Mock-up

Drawing Model

System aspects that can be modelled

When a model activity is undertaking two aspects of the System can be captured:

• Structural aspect: the ‘what’ of the System; it captures what elements a system is made of (e.g., it helps to define the product breakdown structure – PBS) and the relationships between the elements.

• Behavioural aspect: the ‘how’ of the System; how the system elements behave, how elements interact with one another and under what conditions.

A good modelling approach must always consider both the ‘what’ and the ‘how’ regardless of the System, even if we are considering a system such as a database, there is the need to consider how the various stakeholder behave towards it.

When should be considered to model

Modelling can be applied at any product or service stage development. Some examples are captured below (not an extensive list):

• Modelling can be applied whenever there is the need to understand a system or something.

• Modelling can be applied within a small-medium enterprise (SME), start-up or big organisations.

• Modelling can be applied at any point in the Life Cycle, for example, stakeholder needs elicitation by doing “quick and dirty” iterations and scenarios explorations or at later and more detailed development stages.

• Modelling efforts should be applied when only adding value.

Considerations when preparing for MBSE modelling

There are aspects that need to be considered when doing modelling activities: tools, language or notation and people. All this aspects need also to consider planning and scope of a modelling effort as described in the Planning for success with MBSE Arcadia.

Tools

As a model is not merely a collection of representations, but an integrated repository of project knowledge, one or more tools are typically required. These tools must not only provide the necessary capability in terms of language support but should also integrate with each other to ensure completeness, correctness, and consistency across the project.

Language or notation

Standard Techniques and Representations MBSE is most effective when standard techniques and representations are employed. The use of standards improves consistency and facilitates interoperability of tools, people, and process.

People

It is good practise to ensure the appropriate capabilities in modelling languages and tools does not have to be limited to project personnel. MBSE provides the maximum benefit when no translation of the model is required for the stakeholders, Training and support must be provided.

What MBSE is not

Quite common there are myths around MBSE. Hereafter, it will be presented what MBSE is not.

Arcadia / SysML

A representation should use the most appropriate notation for the project. Arcadia and SysML are a very powerful modelling language, however, other languages (e.g., textual, mathematical) also exist and should be chosen on their individual merits.

Simulation

A representation can be either static or dynamic (simulation). Simulation enhances and provides automated and early defects detection.

Part of Systems Engineering activities required on a project

MBSE is an integrated approach to Systems Engineering in which all activities should reference a single point of truth, the model, in order to realise the maximum benefits.

Drawing

A representation (whether graphical, textual, or other) should be connected to the underlying model in order to realise the maximum benefits of MBSE (correctness, completeness, and consistency).

Modelling is MBSE

Modelling forms the core of MBSE, but not all Models are MBSE Models. Modelling and Model-based Engineering (MBE) is extensively in engineering. MBE can be applied to other engineering areas, such as design, and use of bespoke modelling Notations (circuit diagrams, 3-D modelling, CAD, etc.). MBSE, is applied at a higher level and will often be used to harmonise the MBE activities to ensure that the overall System satisfies its original need.

MBSE myths

Model-Based Systems Engineering (MBSE) is an approach that uses models to support the specification, design, analysis, verification, and validation of complex systems. While MBSE offers many benefits, its adoption in organizations can be challenging due to various misconceptions and myths.Some common myths about using and adopting MBSE:Myth: MBSE is Only for Large, Complex Projects.MBSE is only beneficial for large organizations or complex projects with extensive requirements.Reality: While MBSE is particularly advantageous for complex systems, it can also improve clarity, consistency, and communication in smaller projects by providing a structured approach to system design and documentation.Myth: MBSE is a Replacement for Traditional Engineering Practices.Adopting MBSE means completely abandoning traditional engineering methods like document-based approaches.Reality: MBSE complements traditional practices by providing additional tools and methodologies that enhance, rather than replace, conventional systems engineering approaches. It can be integrated into existing workflows to improve overall efficiency and coherence.Myth: MBSE Requires All Engineers to be Experts in Modelling Tools.Successful MBSE implementation requires all team members to become experts in specialized modelling tools.Reality: While some level of tool proficiency is beneficial, not all team members need to be experts. Training and collaboration are key, with a core team skilled in MBSE tools and methodologies supporting others.Myth: MBSE is Too Expensive and Resource-Intensive.MBSE is cost-prohibitive and requires significant resources, making it accessible only to organizations with large budgets.Reality: While there may be initial costs associated with training and tool acquisition (Capella modelling tool is FREE), MBSE can lead to cost savings by reducing errors, improving design efficiency, and enhancing system reliability. The long-term benefits often outweigh the initial investment.Myth: MBSE Produces Too Much Documentation.MBSE creates unnecessary complexity by generating excessive documentation.Reality: MBSE focuses on creating necessary and valuable documentation that enhances understanding and communication. The documentation is often more coherent and integrated than traditional methods, emphasizing quality over quantity.

MBSE in small-scale/start-up environment

As mentioned above, MBSE is used in large project, but can also be used in many of the small-scale/start-up showing common “pain point” that can be addressed by MBSE.Pain Point: Limited Resources and ExpertiseSolution with MBSE: It can streamline the design and development process by providing a structured approach to systems engineering. This helps small teams manage complexity without needing extensive prior experience, reducing the learning curve and helping teams focus on innovation.Pain Point: Rapid Development CyclesSolution with MBSE: The model-based approach facilitates quick iterations and modifications, enabling start-ups to adapt swiftly to changing market demands or technology updates. This agility can be crucial for staying competitive.Pain Point: Integration and Interoperability IssuesSolution with MBSE: It promotes a clear understanding of system components and their interactions, which is vital for integrating various technologies and ensuring they work seamlessly together. This reduces the risk of costly integration issues later in the development cycle.

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