Model Based Systems Engineering Introduction

Systems Engineering Overview

SysML = System Modeling Language

INCOSE = International Council of Systems Engineering

SysML = Object Management Group’s (OMG) SysML = general purpose graphical modeling language for representing systems that may include hardware, software, data, people, facilities and natural objects. Supports practice of model-based system engineering (MBSE).

Systems engineering = multidisciplinary approach to develop balanced system solutions including management and technical processes and mitigate risk that can impact success of project, in response to stakeholder needs.



System Specification and Design process follows these activities:

– Elicit and analyze stakeholder needs = understand problem and how effective the system meets goals

– Specify system = functionality, interfaces, physical and performance, other characteristics

– Synthesize alternative system solutions = partition the system design into components that each satisfy the system requirements

– Perform trade-off analysis = evaluate and select preferred solution that satisfies requirements optimally

– Maintain traceability = path from requirements to the system components and verification and tests



Concept of Operations (ConOps) = what the system is intended to do from the stakeholders’ perspective.

UPDM = Unified Profile for DoDAF / MODAF = describes system of systems (SoS) and enterprise architectures that are compliant to DoDAF and MODAF requirements.


Questions (pg 31)

  1. Demands driving system development are increased capabilities at reduced costs and shorter delivery cycles. Other words its increased functionality, interoperability, performance, reliability, and smaller size.
  2. Purpose of system engineering = see definition above
  3. Key activities of System Specification and Design process = see definition above
  4. Typical stakeholders are diverse, includes the end user as well as manufacturer, supplier, operator, governments,
  5. Different types of requirements are functionality, interoperability, performance, reliability, and size.
  6. Multidisciplinary systems engineering team is important because of diverse stakeholder perspectives
  7. Typical roles of system engineering team is …
  8. Standards are important because it advances and institutionalizes the practice across the industry



Model-Based Systems Engineering

Documents vs MBSE

Requirements use to be documented/stored in a specification tree – a hierarchy that can be used for requirements traceability; systems engineering management plan (SEMP) documents how the process is employed on the project and shows relationships of the engineering disciplines and documents how these groups work together to satisfy the requirements in the specification tree.

MBSE was driven by CAD in 1980s, then UML in 1990s (for software) and increase with technology advancement in modeling and simulation. Official definition:

MBSE = model based systems engineering = formalized application of modeling to support system requirements, design, analysis, verification, and validation activities through the system life cycle.

MBSE is a shift in emphasis from controlling the documentation of the system to controlling the model of the system. Integrates system requirements, design, verification on multiple aspects of the system in a cohesive manner rather than disparate collection of individual documents. Some of MBSE benefits are:

– Enhanced communication = integrates views of system, shares across all teams and stakeholders

– Reduced development risk = ongoing requirements validation/verification; accurate cost estimates

– Improved quality = more rigorous traceability between requirements, design, analysis and testing

– Increased Productivity = reuse, faster, reduced errors, automation

– Enhanced knowledge transfer = use of standards that can be queried and reported

System model = result of modeling tool and contained in model repository. This includes specification, design, analysis, and verification information. This can also be integrated with engineering analysis and simulation models, to perform computation and dynamic execution. Model elements are stored in a model repository.



Model and MBSE method definition

Model = representation of some concept that may be realized in the physical world (a domain of interest). An abstraction.

Method = set of related activities, techniques and conventions that implement one or more processes (usually by using a tool).

Model purpose = determines the scope of the modeling effort in terms of model breadth, depth and fidelity. Some purposes may be:

– Characterize an existing system

– Specify and design a new or modified system

– Evaluate the system

– Train users on how to operate or maintain a system

Good model = meets its intended purpose; there can be good models in poor designs

Good design = how well the design satisfies its requirements and the extent to which it incorporates quality design principles; there could be poor models in good design

Scope of the model = defined in terms of its breadth, depth, and fidelity (amount of detail)



Model Based Metrics

Metrics for model-based system can be based on metrics for traditional document-centric designs; which includes assessing requirements satisfaction, critical performance properties, and quality of design partition. Metrics can help these areas:

– Quality of design = Requirements traceability, from mission-level all the way down to component-level; design partitioning can be measured in terms of the level of cohesion and coupling.

– Show progress of the design and development effort = set completion criteria

– Estimated effort to complete design and development = Constructive Systems Engineering Cost Model (COSYSMO) used for estimating cost and effort for systems engineering activities. Sizing parameters can be done by looking at number of following:

o Requirements

o Use Cases

o Scenarios

o States

o Interfaces

o Activities or operations

o Properties

o Component types (hdware, software, data, procedures)

o Test cases



SysML is one facet of MBSE

MBSE is opposite of Document-Based Approach, which consists of:

o CONOPS – concept of operations

o RTVM = requirements specifications requirement traceability and verification

o IDD – interface definition document

o N2 (N squared) – matrices of structural interfaces

o ADD – architecture description document

o SDS – System design specifications

o Test case specifications

o Specialty engineering analysis

– Three pillars of MBSE

o Modeling Language

  • Graphical Languages = SysML, UML, UPDM, BPMN, MARTE, SoaML, IDEFx
  • Textual Languages = Verilog, Modelica

o Modeling Method

  • The method is a purpose or end goal
  • SysML is not a method but a language that can be used to implement a method (SysML is method independent)
  • Methods:
  • INCOSE Object-Oriented Systems Engineering Method (OOSEM)
  • Welkiens System Modeling (SYSMOD)
  • IBM Telelogic Harmony-SE

o Modeling Tool

  • Unlike Diagramming Tool (Visio, SmartDraw, etc) – modeling tools have specific relationships from the diagram to the model underneath it (ie change a diagram and the system model below it with all dependencies also change)
  • Tools:
  • Agilian (Visual Paradigm)
  • Artisan Studio (Atego)
  • Cameo Systems Modeler (No Magic)
  • Rhapsody (IBM Rational)
  • UModel (Altova)
  • Modelio
  • Papyrus