Preface

Systems engineering is a multidisciplinary approach for developing solutions to complex problems. The increase in system complexity is demanding more rigorous and formalized systems engineering practices. In response to this demand, along with advancements in computer technology, the practice of systems engineering is undergoing a fundamental transition from a document-based approach to a model-based approach. In the model-based approach, the emphasis shifts from producing and controlling documentation to producing and controlling a coherent model of the system. Model-based systems engineering (MBSE) can help to manage complexity, while at the same time improve design quality and cycle time, improve communications among a diverse development team, and facilitate knowledge capture and design evolution.

A standardized and robust modeling language is considered a critical enabler for MBSE. The Systems Modeling Language (OMG SysMLâ„¢) is a general-purpose modeling language that supports the specification, design, analysis, and verification of systems. These systems may include hardware, software, data, personnel, procedures, and facilities. SysML is a graphical modeling language with a semantic foundation for representing requirements, behavior, structure, and properties of the system and its components. The modeling language is intended to model systems from a broad range of industry domains such as aerospace, automotive, health care, and so on.

SysML is an extension of the Unified Modeling Language (UML), version 2, which has become the de facto standard software modeling language. Requirements were issued by the Object Management Group (OMG) in March 2003 to extend UML to support systems modeling. UML 2 was selected as the basis for SysML because it is a robust language that addresses many of the systems engineering needs, while at the same time, the systems engineering community is able to leverage the broad base of experience and tool vendors that support UML. This approach also facilitates the integration of systems and software modeling, which is becoming increasingly important for today’s software-intensive systems.

The development of the language specification was a collaborative effort between members of the OMG, the International Council on Systems Engineering (INCOSE), and the AP233 Working Group of the International Standards Organization (ISO). Following three years of development, the OMG SysML specification was adopted by the OMG in May 2006 and the formal version 1.0 language specification was released in September 2007. Several vendors have now implemented SysML in their tools. It is expected that OMG SysML will continue to evolve through further revisions to the specification based on feedback from end users, tool vendors, and research activities. Information on SysML is available on the official OMG SysML Web site at http://www.omgsysml.org.

This book provides the foundation for understanding and applying SysML to model systems as part of a model-based systems engineering approach. The book is organized into four parts including the Introduction, Language Description, Modeling Examples, and Transitioning to Model-Based Systems Engineering.

Part I, Introduction, contains an overview of systems engineering, a summary of key MBSE concepts, followed by an overview of SysML. The systems engineering overview and MBSE concepts in Chapters 1 and 2 set the context for SysML, and the language overview in Chapter 3 illustrates how the language is applied to a simple example.

Part II, Language Description, provides the detailed description of the language. Chapter 4 provides an overview of the language architecture, and Chapters 5 through 14 describe key concepts related to model organization, blocks, parametrics, activities, interactions, states, use cases, requirements, allocations, and profiles. The ordering of the chapters and the concepts are not based on the ordering of activities in the systems engineering process, but are based on the dependencies between the language concepts. Each chapter builds the readers’ understanding of the concepts by introducing language constructs: their meaning, notation, and examples of how they are used. The example used to demonstrate the language throughout Part II is a security surveillance system. This example should be understandable to most readers and has sufficient complexity to demonstrate the language concepts.

Part III, Modeling Examples, includes two examples to illustrate how SysML can support different model-based methods. The first example in Chapter 15 applies to the design of a water distiller system. It uses a simplified version of a classic functional analysis and allocation method that is applied to the design of a system that primarily controls physical processes. The second example in Chapter 16 applies to the design of a residential security system. It uses a comprehensive object-oriented systems engineering method (OOSEM) and emphasizes how the language is used to address a wide variety of systems engineering concerns, including black-box versus white-box design, logical versus physical design, and system distribution. While these two methods are considered representative of how systems engineering can be applied, SysML is intended to support a variety of other systems engineering methods.

Part IV, Transitioning to Model-Based Systems Engineering, addresses how to transition SysML into an organization. Chapter 17 is about how to integrate SysML into a systems development environment. It describes the type of data that are exchanged between a SysML tool and other classes of tools, and some of the types of data exchange mechanisms that can be used. The chapter also includes a discussion on the criteria for selecting a SysML tool. Chapter 18 in this part, and the last chapter of the book, describes how to deploy SysML into an organization. SysML is introduced into the organization along with model-based methods, tools, and training as part of a carefully planned and implemented improvement process.

Questions are included at the end of each chapter to test readers’ understanding of the material. The answers to the questions can be found on the following Web site at http://www.elsevierdirect.com/companions/9780123743794.

The Appendix contains the SysML notation tables. These tables provide a reference guide for SysML notation along with a cross reference to the applicable sections in Part II of the book.

This book is a “practical guide” targeted to a broad spectrum of industry practitioners and students. It can serve as an introduction and reference for practitioners, as well as an introductory text for courses in systems modeling and its application to model-based systems engineering. In addition, because SysML reuses many UML concepts, software engineers familiar with UML can use this information as a basis for understanding systems engineering concepts. This will also help to bridge gaps in understanding between team members who have diverse expertise, such as is often the case with integrated systems and software engineering teams. Finally, many systems engineering concepts come to light when using an expressive language, and as such, this book can be used to help teach systems engineering concepts.

A first-time reader should pay close attention to the introductory chapters, may choose to do a cursory reading of Part II, and then review the simplified distiller example in Part III. A more advanced reader may choose to read the introductory chapters, do a more comprehensive review of Part II, and then review the residential security example in Part III. Part IV is of general interest to those interested in trying to introduce SysML and MBSE into their organization or project.