Overview

Model-Based Systems Engineering (MBSE) - the use of computer based models of one or more aspects of a system can aid understanding, communication and specification of a system and its behaviour, its structure or architecture or its robustness / susceptability to external threats or internal failures. Typically one or more models will be used as the master sources for data used in the design and development of the system.

Although the 'MBSE' term is often misleadingly used to refer only to architecture descriptions using the UML or the SysML languages MBSE applies to any type and implementation of model. Similarly models have and are being used in all engineering disciplines so the notion that there is something specific for Systems Engineering isn't true. MBSE is therefore a poor and misleading term for what ought to be good practice in engineering as a whole.

Models also support traceability to requirements may themselves be created in another model and if done propertly improve consistency, embed a systematic approach to system/requirement discovery and definition which can reveal gaps and support design justification and validation through audit and engineering reviews.

Models may include:-

• requirement models developed in tools such as DOORS / DOORS Next and exchanged using formats such as ReqIF
• performance / simulations using anything from FORTRAN to Simulink / Matlab, specialist code and computation for aerodynamics or fluid dynamics
• reliability / bottom-up FMECA models to support life predictions / maintenance and repair policy and safety calculations for a design
• top-down Fault Tree Analysis (FTA) to support safety / critical and common mode event path identification for a design
• architecture description using the UML and / or SysML modelling languages to support the definition of system architecture, system states and the functionality, boundaries, interfaces or each system part and thus the system requirements for each part.

The advantages of a model may include:-

• improved consistency
• as a form of rapid protoyping - earlier exploration of important design aspect, factors, parameters before the expense of "cutting metal"
• rapid iteration
• the potential to link multiple design inputs together / improve traceability (dependent on the tool, model, author and IT infrastructure)
• a model can be used to automate part of the development document set

Models and modelling needs to be an integral part of the design and development process to fully realise the advantages. A model, like any other tool, does not solve problems simply because it exists:

• What is the purpose of the particular model? Is it a performance model, design model, safety model etc? Does it need to be static, dynamic, real time/non-real time etc?
• How / does it fit in with or support other models?
• How is the model scope, build and change controlled?
• What sources of information does it depend on?
• What is the fidelity required? How is its quality measured?
• Who needs to be able to understand the model, the notation used? What technical experties or knowledge is required for effective assurance?
• How / do processes and guidelines support modelling?
• How / does does the existing tooling environment, including enterprise change/version control, support modelling? What are the exchange or interoperability requirements?

Eclectica Systems Ltd has a breadth of experience with the management and use of models having started in defence with the use and integration of mathematical models, the development of requirement models (DOORS "classic", DOORS Next Generation). This includes the preparation of technical plans as part of the overall Systems Engineering Management Plan (SEMP) for modelling and requirement management.

Over the last 15 years, Eclectica Systems Ltd has been involved in the procurement, deployment, roll-out and maintenance of architecture description / enterprise architecture tools, models and repositories. To support this Eclectica Systems Ltd is co-creator of the open source TRAK architecture framework and the UML and SysML profiles that implement it. We also created the MDG plugin that implements TRAK for Sparx Systems Enterprise Architect UML modelling tool. We have also created custom domain-specific architecture frameworks and the corresponding UML + SysML profiles as MDG plugins

We have evaluated requirement management tools for clients whilst using them to develop classic SE artefacts such as a Stakeholder Requirement Document and a set of System Requirement Documents and Architecture Definition Documents to evaluate design traceability.

To support the data architecture definition for the Network Rail Intelligent Infrastructure programme Track project we have also created a custom MDG to support the creation of a logical data model / complete with data quality attributes and the model-based generation of information specifications for each design iteration as part of an agile development programme.