SYSTEMS ENGINEERING PRINCIPLES AND
PRACTICE SECOND EDITION
Alexander Kossiakoff William N. Sweet
Samuel J. Seymour Steven M. Biemer
A JOHN WILEY & SONS, INC. PUBLICATION
ffirs02.indd iiiffirs02.indd iii 2/8/2011 11:05:45 AM2/8/2011 11:05:45 AM
ffirs04.indd viffirs04.indd vi 2/8/2011 11:05:47 AM2/8/2011 11:05:47 AM
PRINCIPLES AND PRACTICE
ffirs.indd iffirs.indd i 2/8/2011 11:05:44 AM2/8/2011 11:05:44 AM
WILEY SERIES IN SYSTEMS ENGINEERING AND MANAGEMENT
Andrew P. Sage, Editor
A complete list of the titles in this series appears at the end of this volume.
ffirs01.indd iiffirs01.indd ii 2/8/2011 11:05:44 AM2/8/2011 11:05:44 AM
SYSTEMS ENGINEERING PRINCIPLES AND
PRACTICE SECOND EDITION
Alexander Kossiakoff William N. Sweet
Samuel J. Seymour Steven M. Biemer
A JOHN WILEY & SONS, INC. PUBLICATION
ffirs02.indd iiiffirs02.indd iii 2/8/2011 11:05:45 AM2/8/2011 11:05:45 AM
Copyright © 2011 by John Wiley & Sons, Inc. All rights reserved.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission.
Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifi cally disclaim any implied warranties of merchantability or fi tness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profi t or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com.
Library of Congress Cataloging-in-Publication Data:
Systems engineering : principles and practice/Alexander Kossiakoff … [et al.].—2nd ed. p. cm.—(Wiley series in systems engineering and management; 67) Rev. ed. of: Systems engineering: principles and practices/Alexander Kossiakoff, William N. Sweet. 2003. ISBN 978-0-470-40548-2 (hardback) 1. Systems engineering. I. Kossiakoff, Alexander, 1945– II. Title. TA168.K68 2010 620.001′171–dc22 2010036856
Printed in the United States of America
oBook ISBN: 9781118001028 ePDF ISBN: 9781118001011 ePub ISBN: 9781118009031
10 9 8 7 6 5 4 3 2 1
ffirs03.indd ivffirs03.indd iv 2/8/2011 11:05:46 AM2/8/2011 11:05:46 AM
To Alexander Kossiakoff,
who never took “ no ” for an answer and refused to believe that anything was impossible. He was an extraordinary problem solver, instructor, mentor, and
Samuel J. Seymour
Steven M. Biemer
ffirs04.indd vffirs04.indd v 2/8/2011 11:05:47 AM2/8/2011 11:05:47 AM
ffirs04.indd viffirs04.indd vi 2/8/2011 11:05:47 AM2/8/2011 11:05:47 AM
LIST OF ILLUSTRATIONS xiii
LIST OF TABLES xvii
PREFACE TO THE SECOND EDITION xix
PREFACE TO THE FIRST EDITION xxiii
PART I FOUNDATIONS OF SYSTEMS ENGINEERING 1
1 SYSTEMS ENGINEERING AND THE WORLD OF MODERN SYSTEMS 3
1.1 What Is Systems Engineering? 3
1.2 Origins of Systems Engineering 5
1.3 Examples of Systems Requiring Systems Engineering 10
1.4 Systems Engineering as a Profession 12
1.5 Systems Engineer Career Development Model 18
1.6 The Power of Systems Engineering 21
1.7 Summary 23
Further Reading 26
2 SYSTEMS ENGINEERING LANDSCAPE 27 2.1 Systems Engineering Viewpoint 27
2.2 Perspectives of Systems Engineering 32
2.3 Systems Domains 34
2.4 Systems Engineering Fields 35
2.5 Systems Engineerng Approaches 36
2.6 Systems Engineering Activities and Products 37
2.7 Summary 38
Further Reading 40
ftoc.indd viiftoc.indd vii 2/8/2011 11:05:50 AM2/8/2011 11:05:50 AM
3 STRUCTURE OF COMPLEX SYSTEMS 41 3.1 System Building Blocks and Interfaces 41
3.2 Hierarchy of Complex Systems 42
3.3 System Building Blocks 45
3.4 The System Environment 51
3.5 Interfaces and Interactions 58
3.6 Complexity in Modern Systems 60
3.7 Summary 64
Further Reading 67
4 THE SYSTEM DEVELOPMENT PROCESS 69 4.1 Systems Engineering through the System Life Cycle 69
4.2 System Life Cycle 70
4.3 Evolutionary Characteristics of the Development Process 82
4.4 The Systems Engineering Method 87
4.5 Testing throughout System Development 103
4.6 Summary 106
Further Reading 109
5 SYSTEMS ENGINEERING MANAGEMENT 111 5.1 Managing System Development and Risks 111
5.2 WBS 113
5.3 SEMP 117
5.4 Risk Management 120
5.5 Organization of Systems Engineering 128
5.6 Summary 132
Further Reading 134
PART II CONCEPT DEVELOPMENT STAGE 137
6 NEEDS ANALYSIS 139 6.1 Originating a New System 139
6.2 Operations Analysis 146
6.3 Functional Analysis 151
6.4 Feasibility Defi nition 153
ftoc.indd viiiftoc.indd viii 2/8/2011 11:05:50 AM2/8/2011 11:05:50 AM
6.5 Needs Validation 155
6.6 System Operational Requirements 158
6.7 Summary 162
Further Reading 164
7 CONCEPT EXPLORATION 165 7.1 Developing the System Requirements 165
7.2 Operational Requirements Analysis 170
7.3 Performance Requirements Formulation 178
7.4 Implementation of Concept Exploration 185
7.5 Performance Requirements Validation 189
7.6 Summary 191
Further Reading 194
8 CONCEPT DEFINITION 197 8.1 Selecting the System Concept 197
8.2 Performance Requirements Analysis 201
8.3 Functional Analysis and Formulation 206
8.4 Functional Allocation 212
8.5 Concept Selection 214
8.6 Concept Validation 217
8.7 System Development Planning 219
8.8 Systems Architecting 222
8.9 System Modeling Languages: Unifi ed Modeling Language (UML) and Systems Modeling Language (SysML) 228
8.10 Model-Based Systems Engineering (MBSE) 243
8.11 System Functional Specifi cations 246
8.12 Summary 247
Further Reading 252
9 DECISION ANALYSIS AND SUPPORT 255 9.1 Decision Making 256
9.2 Modeling throughout System Development 262
9.3 Modeling for Decisions 263
9.4 Simulation 272
ftoc.indd ixftoc.indd ix 2/8/2011 11:05:50 AM2/8/2011 11:05:50 AM
9.5 Trade-Off Analysis 282
9.6 Review of Probability 295
9.7 Evaluation Methods 299
9.8 Summary 308
Further Reading 312
PART III ENGINEERING DEVELOPMENT STAGE 315
10 ADVANCED DEVELOPMENT 317 10.1 Reducing Program Risks 317
10.2 Requirements Analysis 322
10.3 Functional Analysis and Design 327
10.4 Prototype Development as a Risk Mitigation Technique 333
10.5 Development Testing 340
10.6 Risk Reduction 349
10.7 Summary 350
Further Reading 354
11 SOFTWARE SYSTEMS ENGINEERING 355 11.1 Coping with Complexity and Abstraction 356
11.2 Nature of Software Development 360
11.3 Software Development Life Cycle Models 365
11.4 Software Concept Development: Analysis and Design 373
11.5 Software Engineering Development: Coding and Unit Test 385
11.6 Software Integration and Test 393
11.7 Software Engineering Management 396
11.8 Summary 402
Further Reading 406
12 ENGINEERING DESIGN 409 12.1 Implementing the System Building Blocks 409
12.2 Requirements Analysis 414
12.3 Functional Analysis and Design 416
12.4 Component Design 419
12.5 Design Validation 432
ftoc.indd xftoc.indd x 2/8/2011 11:05:50 AM2/8/2011 11:05:50 AM
12.6 CM 436
12.7 Summary 439
Further Reading 442
13 INTEGRATION AND EVALUATION 443 13.1 Integrating, Testing, and Evaluating the Total System 443
13.2 Test Planning and Preparation 450
13.3 System Integration 455
13.4 Developmental System Testing 462
13.5 Operational Test and Evaluation 467
13.6 Summary 475
Further Reading 478
PART IV POSTDEVELOPMENT STAGE 481
14 PRODUCTION 483 14.1 Systems Engineering in the Factory 483
14.2 Engineering for Production 485
14.3 Transition from Development to Production 489
14.4 Production Operations 492
14.5 Acquiring a Production Knowledge Base 497
14.6 Summary 500
Further Reading 503
15 OPERATIONS AND SUPPORT 505 15.1 Installing, Maintaining, and Upgrading the System 505
15.2 Installation and Test 507
15.3 In-Service Support 512
15.4 Major System Upgrades: Modernization 516
15.5 Operational Factors in System Development 520
15.6 Summary 522
Further Reading 524
ftoc.indd xiftoc.indd xi 2/8/2011 11:05:50 AM2/8/2011 11:05:50 AM
ftoc.indd xiiftoc.indd xii 2/8/2011 11:05:50 AM2/8/2011 11:05:50 AM
1.1 Career opportunities and growth 14 1.2a Technical orientation phase diagram 16 1.2b Technical orientation population density distribution 16 1.3a Systems engineering (SE) career elements derived from quality work
experiences 19 1.3b Components of employer development of systems engineers 19 1.4 “ T ” model for systems engineer career development 20 2.1a Performance versus cost 29 2.1b Performance/cost versus cost 29 2.2 The ideal missile design from the viewpoint of various specialists 31 2.3 The dimensions of design, systems engineering, and project planning
and control 32 2.4 Systems engineering domains 34 2.5 Examples of systems engineering fi elds 35 2.6 Examples of systems engineering approaches 36 2.7 Life cycle systems engineering view 37 3.1 Knowledge domains of systems engineer and design specialist 45 3.2 Context diagram 53 3.3 Context diagram for an automobile 54 3.4 Environments of a passenger airliner 56 3.5 Functional interactions and physical interfaces 59 3.6 Pyramid of system hierarchy 63 4.1 DoD system life cycle model 71 4.2 System life cycle model 72 4.3 Principal stages in system life cycle 75 4.4 Concept development phases of system life cycle 76 4.5 Engineering development phases in system life cycle 78 4.6 Principal participants in a typical aerospace system development 86 4.7 DoD MIL – STD499B 90 4.8 IEEE – 1220 systems engineering process 90 4.9 EIA – 632 systems engineering process 91
LIST OF ILLUSTRATIONS
fbetw01.indd xiiifbetw01.indd xiii 2/9/2011 6:29:47 PM2/9/2011 6:29:47 PM
xiv LIST OF ILLUSTRATIONS
4.10 ISO – 15288 Systems engineering process 92 4.11 Systems engineering method top – level fl ow diagram 92 4.12 Systems engineering method fl ow diagram 94 4.13 Spiral model of the defense system life cycle 104 5.1 Systems engineering as a part of project management 112 5.2 Place of SEMP in program management plans 118 5.3 Variation of program risk and effort throughout system development 121 5.4 Example of a risk mitigation waterfall chart 122 5.5 An example of a risk cube display 124 6.1 Needs analysis phase in the system life cycle 140 6.2 Needs analysis phase fl ow diagram 147 6.3 Objectives tree structure 150 6.4 Example objectives tree for an automobile 151 6.5 Analysis pyramid 156 7.1 Concept exploration phase in system life cycle 166 7.2 Concept exploration phase fl ow diagram 170 7.3 Simple requirements development process 171 7.4 Triumvirate of conceptual design 175 7.5 Hierarchy of scenarios 177 7.6 Function category versus functional media 181 8.1 Concept defi nition phase in system life cycle 198 8.2 Concept defi nition phase fl ow diagram 202 8.3 IDEF0 functional model structure 208 8.4 Functional block diagram of a standard coffeemaker 210 8.5 Traditional view of architecture 223 8.6 DODAF version 2.0 viewpoints 227 8.7 UML models 229 8.8 Use case diagram 231 8.9 UML activity diagram 233 8.10 UML sequence diagram 234 8.11 Example of a class association 235 8.12 Example of a class generalization association 236 8.13 Class diagram of the library check – out system 237 8.14 SysML models 237 8.15 SysML requirements diagram 238 8.16 SysML block defi nition 240 8.17 SysML block associations 241 8.18a SysML functional hierarchy tree 242 8.18b SysML activity diagram 242 8.19 Baker ’ s MDSD subprocesses 244 8.20 Baker ’ s information model for MDSD 244 9.1 Basic decision – making process 256 9.2 Traditional hierarchical block diagram 265 9.3 Context diagram of a passenger aircraft 266 9.4 Air defense functional fl ow block diagram 267
fbetw01.indd xivfbetw01.indd xiv 2/9/2011 6:29:47 PM2/9/2011 6:29:47 PM
LIST OF ILLUSTRATIONS xv
9.5 System effectiveness simulation 275 9.6 Hardware – in – the – loop simulation 277 9.7 Virtual reality simulation 280 9.8 Candidate utility functions 289 9.9 Criteria profi le 290 9.10 Union of two events 297 9.11 Conditional events 297 9.12 AHP example 300 9.13 AHP results 301 9.14 Decision tree example 302 9.15 Decision path 302 9.16 Decision tree solved 303 9.17 Utility function 304 9.18 Decision tree solved with a utility function 304 9.19 Example of cost – effectiveness integration 305 9.20 QFD house of quality 307 10.1 Advanced development phase in system life cycle 318 10.2 Advanced development phase fl ow diagram 321 10.3 Test and evaluation process of a system element 345 11.1 IEEE software systems engineering process 357 11.2 Software hierarchy 359 11.3 Notional 3 – tier architecture 359 11.4 Classical waterfall software development cycle 367 11.5 Software incremental model 369 11.6 Spiral model 370 11.7 State transition diagram in concurrent development model 371 11.8 User needs, software requirements and specifi cations 376 11.9 Software generation process 376 11.10 Principles of modular partitioning 379 11.11 Functional fl ow block diagram example 381 11.12 Data fl ow diagram: library checkout 381 11.13 Robustness diagram: library checkout 384 12.1 Engineering design phase in system life cycle 410 12.2 Engineering design phase in relation to integration and evaluation 411 12.3 Engineering design phase fl ow diagram 413 13.1 Integration and evaluation phase in system life cycle 445 13.2 Integration and evaluation phase in relation to engineering design 445 13.3 System test and evaluation team 446 13.4 System element test confi guration 456 13.5 Subsystems test confi guration 459 13.6a Operation of a passenger airliner 469 13.6b Operational testing of an airliner 469 13.7 Test realism versus cost 471 14.1 Production phase in system life cycle 484 14.2 Production phase overlap with adjacent phases 485
fbetw01.indd xvfbetw01.indd xv 2/9/2011 6:29:47 PM2/9/2011 6:29:47 PM
xvi LIST OF ILLUSTRATIONS
14.3 Production operation system 494 15.1 Operations and support phase in system life cycle 506 15.2 System operations history 507 15.3 Non – disruptive installation via simulation 510 15.4 Non – disruptive installation via a duplicate system 511
fbetw01.indd xvifbetw01.indd xvi 2/9/2011 6:29:47 PM2/9/2011 6:29:47 PM
1.1 Examples of Engineered Complex Systems: Signal and Data Systems 11 1.2 Examples of Engineered Complex Systems: Material and Energy
Systems 11 2.1 Comparison of Systems Perspectives 33 2.2 Systems Engineering Activities and Documents 38 3.1 System Design Hierarchy 43 3.2 System Functional Elements 47 3.3 Component Design Elements 49 3.4 Examples of Interface Elements 60 4.1 Evolution of System Materialization through the System Life Cycle 84 4.2 Evolution of System Representation 88 4.3 Systems Engineering Method over Life Cycle 102 5.1 System Product WBS Partial Breakdown Structure 114 5.2 Risk Likelihood 125 5.3 Risk Criticality 125 5.4 Sample Risk Plan Worksheet 128 6.1 Status of System Materialization at the Needs Analysis Phase 143 7.1 Status of System Materialization of the Concept Exploration Phase 168 8.1 Status of System Materialization of Concept Defi nition Phase 200 8.2 Use Case Example — “ Check – out Book ” 232 9.1 Decision Framework 259 9.2 Simon’s Decision Process 261 9.3 Weighted Sum Integration of Selection Criteria 288 9.4 Weighted Sum of Actual Measurement 289 9.5 Weighted Sum of Utility Scores 290 9.6 Trade-Off Matrix Example 293 10.1 Status of System Materialization at the Advanced Development Phase 320 10.2 Development of New Components 326 10.3 Selected Critical Characteristics of System Functional Elements 329 10.4 Some Examples of Special Materials 335 11.1 Software Types 361
LIST OF TABLES
fbetw02.indd xviifbetw02.indd xvii 2/9/2011 6:29:55 PM2/9/2011 6:29:55 PM
xviii LIST OF TABLES
11.2 Categories of Software – Dominated Systems 362 11.3 Differences between Hardware and Software 364 11.4 Systems Engineering Life Cycle and the Waterfall Model 368 11.5 Commonly Used Computer Languages 387 11.6 Some Special – Purpose Computer Languages 388 11.7 Characteristics of Prototypes 390 11.8 Comparison of Computer Interface Modes 391 11.9 Capability Levels 398 11.10 Maturity Levels 399 12.1 Status of System Materialization at the Engineering Design Phase 412 12.2 Confi guration Baselines 437 13.1 Status of System Materialization at the Integration and Evaluation Phase 448 13.2 System Integration and Evaluation Process 449 13.3 Parallels between System Development and Test and Evaluation
(T & E) Planning 451
fbetw02.indd xviiifbetw02.indd xviii 2/9/2011 6:29:55 PM2/9/2011 6:29:55 PM
It is an incredible honor and privilege to follow in the footsteps of an individual who had a profound infl uence on the course of history and the fi eld of systems engineering. Since publication of the fi rst edition of this book, the fi eld of systems engineering has seen signifi cant advances, including a signifi cant increase in recognition of the disci- pline, as measured by the number of conferences, symposia, journals, articles, and books available on this crucial subject. Clearly, the fi eld has reached a high level of maturity and is destined for continued growth. Unfortunately, the fi eld has also seen some sorrowful losses, including one of the original authors, Alexander Kossiakoff, who passed away just 2 years after the publication of the book. His vision, innovation, excitement, and perseverance were contagious to all who worked with him and he is missed by the community. Fortunately, his vision remains and continues to be the driving force behind this book. It is with great pride that we dedicate this second edition to the enduring legacy of Alexander Ivanovitch Kossiakoff.
ALEXANDER KOSSIAKOFF, 1914 – 2005
Alexander Kossiakoff, known to so many as “ Kossy, ” gave shape and direction to the Johns Hopkins University Applied Physics Laboratory as its director from 1969 to 1980. His work helped defend our nation, enhance the capabilities of our military, pushed technology in new and exciting directions, and bring successive new genera- tions to an understanding of the unique challenges and opportunities of systems engi- neering. In 1980, recognizing the need to improve the training and education of technical professionals, he started the master of science degree program at Johns Hopkins University in Technical Management and later expanded it to Systems Engineering, one of the fi rst programs of its kind.
Today, the systems engineering program he founded is the largest part – time gradu- ate program in the United States, with students enrolled from around the world in classroom, distance, and organizational partnership venues; it continues to evolve as the fi eld expands and teaching venues embrace new technologies, setting the standard for graduate programs in systems engineering. The fi rst edition of the book is the foun- dational systems engineering textbook for colleges and universities worldwide.
PREFACE TO THE SECOND EDITION
fpref01.indd xixfpref01.indd xix 2/8/2011 3:49:23 PM2/8/2011 3:49:23 PM
xx PREFACE TO THE SECOND EDITION
OBJECTIVES OF THE SECOND EDITION
Traditional engineering disciplines do not provide the training, education, and experi- ence necessary to ensure the successful development of a large, complex system program from inception to operational use. The advocacy of the systems engineering viewpoint and the goal for the practitioners to think like a systems engineer are still the major premises of this book.
This second edition of Systems Engineering Principles and Practice continues to be intended as a graduate – level textbook for courses introducing the fi eld and practice of systems engineering. We continue the tradition of utilizing models to assist students in grasping abstract concepts presented in the book. The fi ve basic models of the fi rst edition are retained, with only minor refi nements to refl ect current thinking. Additionally, the emphasis on application and practice is retained throughout and focuses on students pursuing their educational careers in parallel with their professional careers. Detailed mathematics and other technical fi elds are not explored in depth, providing the greatest range of students who may benefi t, nor are traditional engineering disciplines provided in detail, which would violate the book ’ s intended scope.
The updates and additions to the fi rst edition revolve around the changes occurring in the fi eld of systems engineering since the original publication. Special attention was made in the following areas :
• The Systems Engineer ’ s Career. An expanded discussion is presented on the career of the systems engineer. In recent years, systems engineering has been recognized by many companies and organizations as a separate fi eld, and the position of “ systems engineer ” has been formalized. Therefore, we present a model of the systems engineer ’ s career to help guide prospective professionals.
• The Systems Engineering Landscape. The only new chapter introduced in the second edition is titled by the same name and reinforces the concept of the systems engineering viewpoint. Expanded discussions of the implications of this viewpoint have been offered.
• System Boundaries. Supplemental material has been introduced defi ning and expanding our discussion on the concept of the system boundary. Through the use of the book in graduate – level education, the authors recognized an inherent misunderstanding of this concept — students in general have been unable to rec- ognize the boundary between the system and its environment. This area has been strengthened throughout the book.
• System Complexity. Signifi cant research in the area of system complexity is now available and has been addressed. Concepts such as system of systems engineer- ing, complex systems management, and enterprise systems engineering are intro- duced to the student as a hierarchy of complexity, of which systems engineering forms the foundation.
• Systems Architecting. Since the original publication, the fi eld of systems archi- tecting has expanded signifi cantly, and the tools, techniques, and practices of this
fpref01.indd xxfpref01.indd xx 2/8/2011 3:49:23 PM2/8/2011 3:49:23 PM
PREFACE TO THE SECOND EDITION xxi
fi eld have been incorporated into the concept exploration and defi nition chapters. New models and frameworks for both traditional structured analysis and object – oriented analysis techniques are described and examples are provided, including an expanded description of the Unifi ed Modeling Language and the Systems Modeling Language. Finally, the extension of these new methodologies, model – based systems engineering, is introduced.
• Decision Making and Support. The chapter on systems engineering decision tools has been updated and expanded to introduce the systems engineering student to the variety of decisions required in this fi eld, and the modern pro- cesses, tools, and techniques that are available for use. The chapter has also been moved from the original special topics part of the book.
• Software Systems Engineering. The chapter on software systems engineering has been extensively revised to incorporate modern software engineering techniques, principles, and concepts. Descriptions of modern software development life cycle models, such as the agile development model, have been expanded to refl ect current practices. Moreover, the section on capability maturity models has been updated to refl ect the current integrated model. This chapter has also been moved out of the special topics part and introduced as a full partner of advanced development and engineering design.
In addition to the topics mentioned above, the chapter summaries have been refor- matted for easier understanding, and the lists of problems and references have been updated and expanded. Lastly, feedback, opinions, and recommendations from graduate students have been incorporated where the wording or presentation was awkward or unclear.
This book continues to be used to support the core courses of the Johns Hopkins University Master of Science in Systems Engineering program and is now a primary textbook used throughout the United States and in several other countries. Many pro- grams have transitioned to online or distance instruction; the second edition was written with distance teaching in mind, and offers additional examples.
The length of the book has grown, with the updates and new material refl ecting the expansion of the fi eld itself.
The second edition now has four parts:
• Part I . The Foundation of Systems Engineering, consisting of Chapters 1 – 5 , describes the origins and structure of modern systems, the current fi eld of systems engineering, the structured development process of complex systems, and the organization of system development projects.
• Part II . Concept Development, consisting of Chapters 6 – 9 , describes the early stages of the system life cycle in which a need for a new system is demonstrated,
fpref01.indd xxifpref01.indd xxi 2/8/2011 3:49:23 PM2/8/2011 3:49:23 PM
xxii PREFACE TO THE SECOND EDITION
its requirements identifi ed, alternative implementations developed, and key program and technical decisions made.
• Part III . Engineering Development, consisting of Chapters 10 – 13 , describes the later stages of the system life cycle, in which the system building blocks are engineered (to include both software and hardware subsystems) and the total system is integrated and evaluated in an operational environment.
• Part IV . Postdevelopment, consisting of Chapters 14 and 15 , describes the roles of systems in the production, operation, and support phases of the system life cycle and what domain knowledge of these phases a systems engineer should acquire.
Each chapter contains a summary, homework problems, and bibliography.
The authors of the second edition gratefully acknowledge the family of Dr. Kossiakoff and Mr. William Sweet for their encouragement and support of a second edition to the original book. As with the fi rst edition, the authors gratefully acknowledge the many contributions made by the present and past faculties of the Johns Hopkins University Systems Engineering graduate program. Their sharp insight and recommendations on improvements to the fi rst edition have been invaluable in framing this publication. Particular thanks are due to E. A. Smyth for his insightful review of the manuscript.
Finally, we are exceedingly grateful to our families — Judy Seymour and Michele and August Biemer — for their encouragement, patience, and unfailing support, even when they were continually asked to sacrifi ce, and the end never seemed to be within reach.
Much of the work in preparing this book was supported as part of the educational mission of the Johns Hopkins University Applied Physics Laboratory.
Samuel J. Seymour Steven M. Biemer
fpref01.indd xxiifpref01.indd xxii 2/8/2011 3:49:23 PM2/8/2011 3:49:23 PM
Learning how to be a successful systems engineer is entirely different from learning how to excel at a traditional engineering discipline. It requires developing the ability to think in a special way, to acquire the “ systems engineering viewpoint, ” and to make the central objective the system as a whole and the success of its mission. The systems engineer faces three directions: the system user ’ s needs and concerns, the project man- ager ’ s fi nancial and schedule constraints, and the capabilities and ambitions of the engineering specialists who have to develop and build the elements of the system. This requires learning enough of the language and basic principles of each of the three constituencies to understand their requirements and to negotiate balanced solutions acceptable to all. The role of interdisciplinary leadership is the key contribution and principal challenge of systems engineering and it is absolutely indispensable to the successful development of modern complex systems.
Systems Engineering Principles and Practice is a textbook designed to help students learn to think like systems engineers. Students seeking to learn systems engineering after mastering a traditional engineering discipline often fi nd the subject highly abstract and ambiguous. To help make systems engineering more tangible and easier to grasp, the book provides several models: (1) a hierarchical model of complex systems, showing them to be composed of a set of commonly occurring building blocks or components; (2) a system life cycle model derived from existing models but more explicitly related to evolving engineering activities and participants; (3) a model of the steps in the systems engineering method and their iterative application to each phase of the life cycle; (4) a concept of “ materialization ” that represents the stepwise evolution of an abstract concept to an engineered, integrated, and validated system; and (5) repeated references to the specifi c responsibilities of systems engineers as they evolve during the system life cycle and to the scope of what a systems engineer must know to perform these effectively. The book ’ s signifi cantly different approach is intended to complement the several excellent existing textbooks that concentrate on the quantitative and analyti- cal aspects of systems engineering.
PREFACE TO THE FIRST EDITION
fpref02.indd xxiiifpref02.indd xxiii 2/8/2011 3:49:24 PM2/8/2011 3:49:24 PM
xxiv PREFACE TO THE FIRST EDITION
Particular attention is devoted to systems engineers as professionals, their respon- sibilities as part of a major system development project, and the knowledge, skills, and mind – set they must acquire to be successful. The book stresses that they must be inno- vative and resourceful, as well as systematic and disciplined. It describes the special functions and responsibilities of systems engineers in comparison with those of system analysts, design specialists, test engineers, project managers, and other members of the system development team. While the book describes the necessary processes that systems engineers must know and execute, it stresses the leadership, problem – solving, and innovative skills necessary for success.
The function of systems engineering as defi ned here is to “ guide the engineering of complex systems. ” To learn how to be a good guide requires years of practice and the help and advice of a more experienced guide who knows “ the way. ” The purpose of this book is to provide a signifi cant measure of such help and advice through the organized collective experience of the authors and other contributors.
This book is intended for graduate engineers or scientists who aspire to or are already engaged in careers in systems engineering, project management, or engineering management. Its main audience is expected to be engineers educated in a single disci- pline, either hardware or software, who wish to broaden their knowledge so as to deal with systems problems. It is written with a minimum of mathematics and specialized jargon so that it should also be useful to managers of technical projects or organizations, as well as to senior undergraduates.
1.2 ORIGIN AND CONTENTS
The main portion of the book has been used for the past 5 years to support the fi ve core courses of the Johns Hopkins University Master of Science in Systems Engineering program and is thoroughly class tested. It has also been used successfully as a text for distance course offerings. In addition, the book is well suited to support short courses and in – house training.
The book consists of 14 chapters grouped into fi ve parts :
• Part I . The Foundations of Systems Engineering, consisting of Chapters 1 – 4 , describes the origin and structure of modern systems, the stepwise development process of complex systems, and the organization of system development projects.
• Part II . Concept Development, consisting of Chapters 5 – 7 , describes the fi rst stage of the system life cycle in which a need for a new system is demonstrated, its requirements are developed, and a specifi c preferred implementation concept is selected.
• Part III . Engineering Development, consisting of Chapters 8 – 10 , describes the second stage of the system life cycle, in which the system building blocks are engineered and the total system is integrated and evaluated in an operational environment.
fpref02.indd xxivfpref02.indd xxiv 2/8/2011 3:49:24 PM2/8/2011 3:49:24 PM
PREFACE TO THE FIRST EDITION xxv
• Part IV . Postdevelopment, consisting of Chapters 11 and 12 , describes the role of systems engineering in the production, operation, and support phases of the system life cycle, and what domain knowledge of these phases in the system life cycle a systems engineer should acquire.
• Part V . Special Topics consists of Chapters 13 and 14 . Chapter 13 describes the pervasive role of software throughout system development, and Chapter 14 addresses the application of modeling, simulation, and trade – off analysis as systems engineering decision tools.
Each chapter also contains a summary, homework problems, and a bibliography. A glossary of important terms is also included. The chapter summaries are formatted to facilitate their use in lecture viewgraphs.
The authors gratefully acknowledge the many contributions made by the present and past faculties of the Johns Hopkins University Systems Engineering Masters program. Particular thanks are due to S. M. Biemer, J. B. Chism, R. S. Grossman, D. C. Mitchell, J. W. Schneider, R. M. Schulmeyer, T. P. Sleight, G. D. Smith, R. J. Thompson, and S. P. Yanek, for their astute criticism of passages that may have been dear to our hearts but are in need of repairs.
An even larger debt is owed to Ben E. Amster, who was one of the originators and the initial faculty of the Johns Hopkins University Systems Engineering program. Though not directly involved in the original writing, he enhanced the text and diagrams by adding many of his own insights and fi ne – tuned the entire text for meaning and clarity, applying his 30 years ’ experience as a systems engineer to great advantage.
We especially want to thank H. J. Gravagna for her outstanding expertise and inexhaustible patience in typing and editing the innumerable rewrites of the drafts of the manuscript. These were issued to successive classes of systems engineering students as the book evolved over the past 3 years. It was she who kept the focus on the fi nal product and provided invaluable assistance with the production of this work.
Finally, we are eternally grateful to our wives, Arabelle and Kathleen, for their encouragement, patience, and unfailing support, especially when the written words came hard and the end seemed beyond our reach.
Much of the work in preparing this book was supported as part of the educational mission of the Johns Hopkins Applied Physics Laboratory.
Alexander Kossiakoff William N. Sweet
fpref02.indd xxvfpref02.indd xxv 2/8/2011 3:49:24 PM2/8/2011 3:49:24 PM
fpref02.indd xxvifpref02.indd xxvi 2/8/2011 3:49:24 PM2/8/2011 3:49:24 PM
Part I provides a multidimensional framework that interrelates the basic principles of systems engineering, and helps to organize the areas of knowledge that are required to master this subject. The dimensions of this framework include
1. a hierarchical model of the structure of complex systems;
2. a set of commonly occurring functional and physical system building blocks;
3. a systems engineering life cycle, integrating the features of the U.S Department of Defense, ISO/IEC, IEEE, and NSPE models;
4. four basic steps of the systems engineering method that are iterated during each phase of the life cycle;
5. three capabilities differentiating project management, design specialization, and systems engineering;
6. three different technical orientations of a scientist, a mathematician, and an engineer and how they combine in the orientation of a systems engineer; and
7. a concept of “ materialization ” that measures the degree of transformation of a system element from a requirement to a fully implemented part of a real system.
FOUNDATIONS OF SYSTEMS ENGINEERING
Systems Engineering Principles and Practice, Second Edition. Alexander Kossiakoff, William N. Sweet, Samuel J. Seymour, and Steven M. Biemer © 2011 by John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.
p01.indd 1p01.indd 1 2/9/2011 4:16:37 PM2/9/2011 4:16:37 PM
2 FOUNDATIONS OF SYSTEMS ENGINEERING
Chapter 1 describes the origins and characteristics of modern complex systems and systems engineering as a profession.
Chapter 2 defi nes the “ systems engineering viewpoint ” and how it differs from the viewpoints of technical specialists and project managers. This concept of a systems viewpoint is expanded to describe the domain, fi elds, and approaches of the systems engineering discipline.
Chapter 3 develops the hierarchical model of a complex system and the key build- ing blocks from which it is constituted. This framework is used to defi ne the breadth and depth of the knowledge domain of systems engineers in terms of the system hierarchy.
Chapter 4 derives the concept of the systems engineering life cycle, which sets the framework for the evolution of a complex system from a perceived need to operation and disposal. This framework is systematically applied throughout Parts II – IV of the book, each part addressing the key responsibilities of systems engineering in the cor- responding phase of the life cycle.
Finally, Chapter 5 describes the key parts that systems engineering plays in the management of system development projects. It defi nes the basic organization and the planning documents of a system development project, with a major emphasis on the management of program risks.
p01.indd 2p01.indd 2 2/9/2011 4:16:37 PM2/9/2011 4:16:37 PM
1.1 WHAT IS SYSTEMS ENGINEERING?
There are many ways in which to defi ne systems engineering. For the purposes of this book, we will use the following defi nition:
The function of systems engineering is to guide the engineering of complex systems . The words in this defi nition are used in their conventional meanings, as described
further below. To guide is defi ned as “ to lead, manage, or direct, usually based on the superior
experience in pursuing a given course ” and “ to show the way. ” This characterization emphasizes the process of selecting the path for others to follow from among many possible courses — a primary function of systems engineering. A dictionary defi nition of engineering is “ the application of scientifi c principles to practical ends; as the design, construction and operation of effi cient and economical structures, equipment, and systems. ” In this defi nition, the terms “ effi cient ” and “ economical ” are particular con- tributions of good systems engineering.
The word “ system, ” as is the case with most common English words, has a very broad meaning. A frequently used defi nition of a system is “ a set of interrelated
1 SYSTEMS ENGINEERING
AND THE WORLD OF MODERN SYSTEMS
Systems Engineering Principles and Practice, Second Edition. Alexander Kossiakoff, William N. Sweet, Samuel J. Seymour, and Steven M. Biemer © 2011 by John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.
c01.indd 3c01.indd 3 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
4 SYSTEMS ENGINEERING AND THE WORLD OF MODERN SYSTEMS
components working together toward some common objective. ” This defi nition implies a multiplicity of interacting parts that collectively perform a signifi cant function. The term complex restricts this defi nition to systems in which the elements are diverse and have intricate relationships with one another. Thus, a home appliance such as a washing machine would not be considered suffi ciently diverse and complex to require systems engineering, even though it may have some modern automated attachments. On the other hand, the context of an engineered system excludes such complex systems as living organisms and ecosystems. The restriction of the term “ system ” to one that is complex and engineered makes it more clearly applicable to the function of systems engineering as it is commonly understood. Examples of systems requiring systems engineering for their development are listed in a subsequent section.
The above defi nitions of “ systems engineering ” and “ system ” are not represented as being unique or superior to those used in other textbooks, each of which defi nes them somewhat differently. In order to avoid any potential misunderstanding, the meaning of these terms as used in this book is defi ned at the very outset, before going on to the more important subjects of the responsibilities, problems, activities, and tools of systems engineering.
Systems Engineering and Traditional Engineering Disciplines
From the above defi nition, it can be seen that systems engineering differs from mechani- cal, electrical, and other engineering disciplines in several important ways:
1. Systems engineering is focused on the system as a whole; it emphasizes its total operation. It looks at the system from the outside, that is, at its interactions with other systems and the environment, as well as from the inside. It is concerned not only with the engineering design of the system but also with external factors, which can signifi cantly constrain the design. These include the identifi cation of customer needs, the system operational environment, interfacing systems, logis- tics support requirements, the capabilities of operating personnel, and such other factors as must be correctly refl ected in system requirements documents and accommodated in the system design.
2. While the primary purpose of systems engineering is to guide, this does not mean that systems engineers do not themselves play a key role in system design. On the contrary, they are responsible for leading the formative (concept devel- opment) stage of a new system development, which culminates in the functional design of the system refl ecting the needs of the user. Important design decisions at this stage cannot be based entirely on quantitative knowledge, as they are for the traditional engineering disciplines, but rather must often rely on qualitative judgments balancing a variety of incommensurate quantities and utilizing expe- rience in a variety of disciplines, especially when dealing with new technology.
3. Systems engineering bridges the traditional engineering disciplines. The diver- sity of the elements in a complex system requires different engineering disci-
c01.indd 4c01.indd 4 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
ORIGINS OF SYSTEMS ENGINEERING 5
plines to be involved in their design and development. For the system to perform correctly, each system element must function properly in combination with one or more other system elements. Implementation of these interrelated functions is dependent on a complex set of physical and functional interactions between separately designed elements. Thus, the various elements cannot be engineered independently of one another and then simply assembled to produce a working system. Rather, systems engineers must guide and coordinate the design of each individual element as necessary to assure that the interactions and interfaces between system elements are compatible and mutually supporting. Such coor- dination is especially important when individual system elements are designed, tested, and supplied by different organizations.
Systems Engineering and Project Management
The engineering of a new complex system usually begins with an exploratory stage in which a new system concept is evolved to meet a recognized need or to exploit a tech- nological opportunity. When the decision is made to engineer the new concept into an operational system, the resulting effort is inherently a major enterprise, which typically requires many people, with diverse skills, to devote years of effort to bring the system from concept to operational use.
The magnitude and complexity of the effort to engineer a new system requires a dedicated team to lead and coordinate its execution. Such an enterprise is called a “ project ” and is directed by a project manager aided by a staff. Systems engineering is an inherent part of project management — the part that is concerned with guiding the engineering effort itself — setting its objectives, guiding its execution, evaluating its results, and prescribing necessary corrective actions to keep it on course. The man- agement of the planning and control aspects of the project fi scal, contractual, and customer relations is supported by systems engineering but is usually not considered to be part of the systems engineering function. This subject is described in more detail in Chapter 5 .
Recognition of the importance of systems engineering by every participant in a system development project is essential for its effective implementation. To accomplish this, it is often useful to formally assign the leader of the systems engineering team to a recognized position of technical responsibility and authority within the project.
1.2 ORIGINS OF SYSTEMS ENGINEERING
No particular date can be associated with the origins of systems engineering. Systems engineering principles have been practiced at some level since the building of the pyra- mids and probably before. (The Bible records that Noah ’ s Ark was built to a system specifi cation.)
The recognition of systems engineering as a distinct activity is often associated with the effects of World War II, and especially the 1950s and 1960s when a number of textbooks were published that fi rst identifi ed systems engineering as a distinct
c01.indd 5c01.indd 5 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
6 SYSTEMS ENGINEERING AND THE WORLD OF MODERN SYSTEMS
discipline and defi ned its place in the engineering of systems. More generally, the recognition of systems engineering as a unique activity evolved as a necessary corollary to the rapid growth of technology, and its application to major military and commercial operations during the second half of the twentieth century.
The global confl agration of World War II provided a tremendous spur to the advancement of technology in order to gain a military advantage for one side or the other. The development of high – performance aircraft, military radar, the proximity fuse, the German VI and V2 missiles, and especially the atomic bomb required revolutionary advances in the application of energy, materials, and information. These systems were complex, combining multiple technical disciplines, and their development posed engi- neering challenges signifi cantly beyond those that had been presented by their more conventional predecessors. Moreover, the compressed development time schedules imposed by wartime imperatives necessitated a level of organization and effi ciency that required new approaches in program planning, technical coordination, and engineering management. Systems engineering, as we know it today, developed to meet these challenges.
During the Cold War of the 1950s, 1960s, and 1970s, military requirements con- tinued to drive the growth of technology in jet propulsion, control systems, and materi- als. However, another development, that of solid – state electronics, has had perhaps a more profound effect on technological growth. This, to a large extent, made possible the still evolving “ information age, ” in which computing, networks, and communica- tions are extending the power and reach of systems far beyond their previous limits. Particularly signifi cant in this connection is the development of the digital computer and the associated software technology driving it, which increasingly is leading to the replacement of human control of systems by automation. Computer control is qualita- tively increasing the complexity of systems and is a particularly important concern of systems engineering.
The relation of modern systems engineering to its origins can be best understood in terms of three basic factors:
1. Advancing Technology, which provide opportunities for increasing system capabilities, but introduces development risks that require systems engineering management; nowhere is this more evident than in the world of automation. Technology advances in human – system interfaces, robotics, and software make this particular area one of the fastest growing technologies affecting system design.
2. Competition, whose various forms require seeking superior (and more advanced) system solutions through the use of system – level trade – offs among alternative approaches.
3. Specialization, which requires the partitioning of the system into building blocks corresponding to specifi c product types that can be designed and built by specialists, and strict management of their interfaces and interactions.
These factors are discussed in the following paragraphs.
c01.indd 6c01.indd 6 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
ORIGINS OF SYSTEMS ENGINEERING 7
Advancing Technology: Risks
The explosive growth of technology in the latter half of the twentieth century and into this century has been the single largest factor in the emergence of systems engi- neering as an essential ingredient in the engineering of complex systems. Advancing technology has not only greatly extended the capabilities of earlier systems, such as aircraft, telecommunications, and power plants, but has also created entirely new systems such as those based on jet propulsion, satellite communications and navigation, and a host of computer – based systems for manufacturing, fi nance, transportation, entertainment, health care, and other products and services. Advances in technology have not only affected the nature of products but have also fundamentally changed the way they are engineered, produced, and operated. These are particularly important in early phases of system development, as described in Conceptual Exploration, in Chapter 7 .
Modern technology has had a profound effect on the very approach to engineering. Traditionally, engineering applies known principles to practical ends. Innovation, however, produces new materials, devices, and processes, whose characteristics are not yet fully measured or understood. The application of these to the engineering of new systems thus increases the risk of encountering unexpected properties and effects that might impact system performance and might require costly changes and program delays.
However, failure to apply the latest technology to system development also carries risks. These are the risks of producing an inferior system, one that could become pre- maturely obsolete. If a competitor succeeds in overcoming such problems as may be encountered in using advanced technology, the competing approach is likely to be superior. The successful entrepreneurial organization will thus assume carefully selected technological risks and surmount them by skillful design, systems engineering, and program management.
The systems engineering approach to the early application of new technology is embodied in the practice of “ risk management. ” Risk management is a process of dealing with calculated risks through a process of analysis, development, test, and engineering oversight. It is described more fully in Chapters 5 and 9 .
Dealing with risks is one of the essential tasks of systems engineering, requiring a broad knowledge of the total system and its critical elements. In particular, systems engineering is central to the decision of how to achieve the best balance of risks, that is, which system elements should best take advantage of new technology and which should be based on proven components, and how the risks incurred should be reduced by development and testing.
The development of the digital computer and software technology noted earlier deserves special mention. This development has led to an enormous increase in the automation of a wide array of control functions for use in factories, offi ces, hospitals, and throughout society. Automation, most of it being concerned with information pro- cessing hardware and software, and its sister technology, autonomy, which adds in capability of command and control, is the fastest growing and most powerful single infl uence on the engineering of modern systems.
c01.indd 7c01.indd 7 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
8 SYSTEMS ENGINEERING AND THE WORLD OF MODERN SYSTEMS
The increase in automation has had an enormous impact on people who operate systems, decreasing their number but often requiring higher skills and therefore special training. Human – machine interfaces and other people – system interactions are particu- lar concerns of systems engineering.
Software continues to be a growing engineering medium whose power and versatil- ity has resulted in its use in preference to hardware for the implementation of a growing fraction of system functions. Thus, the performance of modern systems increasingly depends on the proper design and maintenance of software components. As a result, more and more of the systems engineering effort has had to be directed to the control of software design and its application.
Competition: Trade – offs
Competitive pressures on the system development process occur at several different levels. In the case of defense systems, a primary drive comes from the increasing mili- tary capabilities of potential adversaries, which correspondingly decrease the effective- ness of systems designed to defeat them. Such pressures eventually force a development program to redress the military balance with a new and more capable system or a major upgrade of an existing one.
Another source of competition comes with the use of competitive contracting for the development of new system capabilities. Throughout the competitive period, which may last through the initial engineering of a new system, each contractor seeks to devise the most cost – effective program to provide a superior product.
In developing a commercial product, there are nearly always other companies that compete in the same market. In this case, the objective is to develop a new market or to obtain an increased market share by producing a superior product ahead of the com- petition, with an edge that will maintain a lead for a number of years. The above approaches nearly always apply the most recent technology in an effort to gain a com- petitive advantage.
Securing the large sums of money needed to fund the development of a new complex system also involves competition on quite a different level. In particular, both government agencies and industrial companies have many more calls on their resources than they can accommodate and hence must carefully weigh the relative payoff of proposed programs. This is a primary reason for requiring a phased approach in new system development efforts, through the requirement for justifi cation and formal approval to proceed with the increasingly expensive later phases. The results of each phase of a major development must convince decision makers that the end objectives are highly likely to be attained within the projected cost and schedule.
On a still different basis, the competition among the essential characteristics of the system is always a major consideration in its development. For example, there is always competition between performance, cost, and schedule, and it is impossible to optimize all three at once. Many programs have failed by striving to achieve levels of performance that proved unaffordable. Similarly, the various performance parame- ters of a vehicle, such as speed and range, are not independent of one another; the effi ciency of most vehicles, and hence their operating range, decreases at higher speeds.
c01.indd 8c01.indd 8 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
ORIGINS OF SYSTEMS ENGINEERING 9
Thus, it is necessary to examine alternatives in which these characteristics are allowed to vary and to select the combination that best balances their values for the benefi t of the user.
All of the forms of competition exert pressure on the system development process to produce the best performing, most affordable system, in the least possible time. The process of selecting the most desirable approach requires the examination of numerous potential alternatives and the exercise of a breadth of technical knowledge and judgment that only experienced systems engineers possess. This is often referred to as “ trade – off analysis ” and forms one of the basic practices of systems engineering.
A complex system that performs a number of different functions must of necessity be confi gured in such a way that each major function is embodied in a separate component capable of being specifi ed, developed, built, and tested as an individual entity. Such a subdivision takes advantage of the expertise of organizations specializing in particular types of products, and hence is capable of engineering and producing components of the highest quality at the lowest cost. Chapter 3 describes the kind of functional and physical building blocks that make up most modern systems.
The immensity and diversity of engineering knowledge, which is still growing, has made it necessary to divide the education and practice of engineering into a number of specialties, such as mechanical, electrical, aeronautical, and so on. To acquire the neces- sary depth of knowledge in any one of these fi elds, further specialization is needed, into such subfi elds as robotics, digital design, and fl uid dynamics. Thus, engineering specialization is a predominant condition in the fi eld of engineering and manufacturing and must be recognized as a basic condition in the system development process.
Each engineering specialty has developed a set of specialized tools and facilities to aid in the design and manufacture of its associated products. Large and small com- panies have organized around one or several engineering groups to develop and manu- facture devices to meet the needs of the commercial market or of the system – oriented industry. The development of interchangeable parts and automated assembly has been one of the triumphs of the U.S. industry.
The convenience of subdividing complex systems into individual building blocks has a price: that of integrating these disparate parts into an effi cient, smoothly operating system. Integration means that each building block fi ts perfectly with its neighbors and with the external environment with which it comes into contact. The “ fi t ” must be not only physical but also functional; that is, its design will both affect the design charac- teristics and behavior of other elements, and will be affected by them, to produce the exact response that the overall system is required to make to inputs from its environ- ment. The physical fi t is accomplished at intercomponent boundaries called interfaces . The functional relationships are called interactions .
The task of analyzing, specifying, and validating the component interfaces with each other and with the external environment is beyond the expertise of the individual design specialists and is the province of the systems engineer. Chapter 3 discusses further the importance and nature of this responsibility.
c01.indd 9c01.indd 9 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
10 SYSTEMS ENGINEERING AND THE WORLD OF MODERN SYSTEMS
A direct consequence of the subdivision of systems into their building blocks is the concept of modularity. Modularity is a measure of the degree of mutual indepen- dence of the individual system components. An essential goal of systems engineering is to achieve a high degree of modularity to make interfaces and interactions as simple as possible for effi cient manufacture, system integration, test, operational maintenance, reliability, and ease of in – service upgrading. The process of subdividing a system into modular building blocks is called “ functional allocation ” and is another basic tool of systems engineering.
1.3 EXAMPLES OF SYSTEMS REQUIRING SYSTEMS ENGINEERING
As noted at the beginning of this chapter, the generic defi nition of a system as a set of interrelated components working together as an integrated whole to achieve some common objective would fi t most familiar home appliances. A washing machine con- sists of a main clothes tub, an electric motor, an agitator, a pump, a timer, an inner spinning tub, and various valves, sensors, and controls. It performs a sequence of timed operations and auxiliary functions based on a schedule and operation mode set by the operator. A refrigerator, microwave oven, dishwasher, vacuum cleaner, and radio all perform a number of useful operations in a systematic manner. However, these appli- ances involve only one or two engineering disciplines, and their design is based on well – established technology. Thus, they fail the criterion of being complex , and we would not consider the development of a new washer or refrigerator to involve much systems engineering as we understand the term, although it would certainly require a high order of reliability and cost engineering. Of course, home appliances increasingly include clever automatic devices that use newly available microchips, but these are usually self – contained add – ons and are not necessary to the main function of the appliance.
Since the development of new modern systems is strongly driven by technological change, we shall add one more characteristic to a system requiring systems engineering, namely, that some of its key elements use advanced technology. The characteristics of a system whose development, test, and application require the practice of systems engineering are that the system
• is an engineered product and hence satisfi es a specifi ed need,
• consists of diverse components that have intricate relationships with one another and hence is multidisciplinary and relatively complex, and
• uses advanced technology in ways that are central to the performance of its primary functions and hence involves development risk and often a relatively high cost.
Henceforth, references in this text to an engineered or complex system (or in the proper context, just system ) will mean the type that has the three attributes noted above, that is, is an engineered product, contains diverse components, and uses advanced technology. These attributes are, of course, in addition to the generic defi nition stated
c01.indd 10c01.indd 10 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
EXAMPLES OF SYSTEMS REQUIRING SYSTEMS ENGINEERING 11
earlier and serve to identify the systems of concern to the systems engineer as those that require system design, development, integration, test, and evaluation. In Chapter 2 , we explore the full spectrum of systems complexity and why the systems engineering landscape presents a challenge for systems engineers.
Examples of Complex Engineered Systems
To illustrate the types of systems that fi t within the above defi nition, Tables 1.1 and 1.2 list 10 modern systems and their principal inputs, processes, and outputs.
TABLE 1.1. Examples of Engineered Complex Systems: Signal and Data Systems
System Inputs Process Outputs
Weather satellite Images • Data storage • Transmission
Terminal air traffi c control system
Aircraft beacon responses
• Identifi cation • Tracking
• Identity • Air tracks • Communications
Track location system Cargo routing requests
• Map tracing • Communication
• Routing information • Delivered cargo
Airline reservation system
Travel requests Data management • Reservations • Tickets
Clinical information system
• Patient ID • Test records • Diagnosis
• Patient status • History • Treatment
TABLE 1.2. Examples of Engineered Complex Systems: Material and Energy Systems
System Inputs Process Outputs
Passenger aircraft • Passengers • Fuel
• Combustion • Thrust • Lift
Modern harvester combine
• Grain fi eld • Fuel
• Cutting • Threshing
Oil refi nery • Crude oil • Catalysts • Energy
• Cracking • Separation • Blending
• Gasoline • Oil products • Chemicals
Auto assembly plant • Auto parts • Energy
• Manipulation • Joining • Finishing
Electric power plant • Fuel • Air
• Power generation • Regulation
• Electric AC power • Waste products
c01.indd 11c01.indd 11 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
12 SYSTEMS ENGINEERING AND THE WORLD OF MODERN SYSTEMS
It has been noted that a system consists of a multiplicity of elements, some of which may well themselves be complex and deserve to be considered a system in their own right. For example, a telephone – switching substation can well be considered as a system, with the telephone network considered as a “ system of systems. ” Such issues will be discussed more fully in Chapters 2 and 4 , to the extent necessary for the under- standing of systems engineering.
Example: A Modern Automobile. A more simple and familiar system, which still meets the criteria for an engineered system, is a fully equipped passenger automo- bile. It can be considered as a lower limit to more complex vehicular systems. It is made up of a large number of diverse components requiring the combination of several different disciplines. To operate properly, the components must work together accu- rately and effi ciently. Whereas the operating principles of automobiles are well estab- lished, modern autos must be designed to operate effi ciently while at the same time maintaining very close control of engine emissions, which requires sophisticated sensors and computer – controlled mechanisms for injecting fuel and air. Antilock brakes are another example of a fi nely tuned automatic automobile subsystem. Advanced materials and computer technology are used to an increasing degree in passenger pro- tection, cruise control, automated navigation and autonomous driving and parking. The stringent requirements on cost, reliability, performance, comfort, safety, and a dozen other parameters present a number of substantive systems engineering problems. Accordingly, an automobile meets the defi nition established earlier for a system requir- ing the application of systems engineering, and hence can serve as a useful example.
An automobile is also an example of a large class of systems that require active interaction (control) by a human operator. To some degree, all systems require such interaction, but in this case, continuous control is required. In a very real sense, the operator (driver) functions as an integral part of the overall automobile system, serving as the steering feedback element that detects and corrects deviations of the car ’ s path on the road. The design must therefore address as a critical constraint the inherent sensing and reaction capabilities of the operator, in addition to a range of associated human – machine interfaces such as the design and placement of controls and displays, seat position, and so on. Also, while the passengers may not function as integral ele- ments of the auto steering system, their associated interfaces (e.g., weight, seating and viewing comfort, and safety) must be carefully addressed as part of the design process. Nevertheless, since automobiles are developed and delivered without the human element, for purposes of systems engineering, they may be addressed as systems in their own right.
1.4 SYSTEMS ENGINEERING AS A PROFESSION
With the increasing prevalence of complex systems in modern society, and the essential role of systems engineering in the development of systems, systems engineering as a profession has become widely recognized. Its primary recognition has come in compa- nies specializing in the development of large systems. A number of these have estab-
c01.indd 12c01.indd 12 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM
SYSTEMS ENGINEERING AS A PROFESSION 13
lished departments of systems engineering and have classifi ed those engaging in the process as systems engineers. In addition, global challenges in health care, communica- tions, environment, and many other complex areas require engineering systems methods to develop viable solutions.
To date, the slowness of recognition of systems engineering as a career is the fact that it does not correspond to the traditional academic engineering disciplines. Engineering disciplines are built on quantitative relationships, obeying established physical laws, and measured properties of materials, energy, or information. Systems engineering, on the other hand, deals mainly with problems for which there is incom- plete knowledge, whose variables do not obey known equations, and where a balance must be made among confl icting objectives involving incommensurate attributes. The absence of a quantitative knowledge base previously inhibited the establishment of systems engineering as a unique discipline.
Despite those obstacles, the recognized need for systems engineering in industry and government has spurred the establishment of a number of academic programs offering master ’ s degrees and doctoral degrees in systems engineering. An increasing number of universities are offering undergraduate degrees in systems engineering as well.
The recognition of systems engineering as a profession has led to the formation of a professional society, the International Council on Systems Engineering (INCOSE), one of whose primary objectives is the promotion of systems engineering, and the recognition of systems engineering as a professional career.
Systems engineers are highly sought after because their skills complement those in other fi elds and often serve as the “ glue ” to bring new ideas to fruition. However, career choices and the related educational needs for those choices is complex, especially when the role and responsibilities of a systems engineer is poorly understood.
Four potential career directions are shown in Figure 1.1 : fi nancial, management, technical, and systems engineering. There are varying degrees of overlap between them despite the symmetry shown in the fi gure. The systems engineer focuses on the whole system product, leading and working with many diverse technical team members, fol- lowing the systems engineering development cycle, conducting studies of alternatives, and managing the system interfaces. The systems engineer generally matures in the fi eld after a technical undergraduate degree with work experience and a master of science degree in systems engineering, with an increasing responsibility of successively larger projects, eventually serving as the chief or lead systems engineer for a major systems, or systems – of – systems development. Note the overlap and need to understand the content and roles of the technical specialists and to coordinate with the program manager (PM).
The project manager or PM, often with a technical or business background, is responsible for interfacing with the customer and for defi ning the work, developing the plans, monitoring and controlling the project progress, and delivering the fi nished output to the customer. The PM often learns from on the job training (OJT) with
c01.indd 13c01.indd 13 2/8/2011 11:04:29 AM2/8/2011 11:04:29 AM