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					                       Chapter 1

              The Systems Engineering Context




Winter 2007              SEG2101 - Chapter 1    1
    What Is Systems Engineering?
Systems Engineering is an interdisciplinary approach and means to enable the realization of
    successful systems. It focuses on defining customer needs and required functionality
    early in the development cycle, documenting requirements, then proceeding with design
    synthesis and system validation while considering the complete problem:

•   Operations
•   Performance
•   Test
•   Manufacturing
•   Cost & Schedule
•   Training & Support
•   Disposal

Winter 2007                         SEG2101 - Chapter 1                                   2
     Systems Engineering Context
• The problem
• Major principles of systems engineering
• Managing the system evolution




Winter 2007      SEG2101 - Chapter 1        3
              1.1: The Problem
•   Symptoms
•   Reasons
•   Quality
•   Traditional approach




Winter 2007        SEG2101 - Chapter 1   4
               Symptoms
• The quality and cost of software has been a
  growing concern
• Delivered long behind schedule
• At much higher cost than anticipated
• Without giving the desired benefits and user
  satisfaction


Winter 2007       SEG2101 - Chapter 1        5
                       Reasons
• It is hard to understand the purpose of a system well
  enough to plan its functionality in advance so that it will
  really satisfy the user needs.
• The complexity of systems and their dynamic behavior is
  too high.
• The visibility nature of the product makes the development
  and maintenance process itself difficult to understand and
  control.
• There is a lack of proven components to use as high level
  building blocks. Too much is developed from scratch.

Winter 2007             SEG2101 - Chapter 1                 6
                                    Concepts
• User: all those who interact directly with the system and
    use the system service to achieve some operative purpose.
• Owner: people that will either own or be responsible for
    the system during part of its lifetime.
• Subject: known to the system but does not directly
    interact with it.   (e.g. people and objects represented in a database)




• Developer: people that actually develop the system.


Winter 2007                                SEG2101 - Chapter 1                7
              System Quality
• System quality is the systems ability to
  satisfy the needs and expectations of the
  user and the owners, i.e. the system
  environment.
• Quality depends on clear and unambiguous
  communication.



Winter 2007      SEG2101 - Chapter 1          8
              Quality




Winter 2007   SEG2101 - Chapter 1   9
              Communication Problem




Winter 2007     SEG2101 - Chapter 1   10
         Essence of Quality Control
• To ensure that each communication link and
  transformation step worked as intended.
     – Overall process: the organization of the development
       process into major steps where specific documents are
       produced and certain quality assessment procedures
       performed.
     – Technical content: the information content in the
       various documents, e.g. requirements specification,
       system specification, and test plans.


Winter 2007              SEG2101 - Chapter 1                   11
              The Traditional Approach




Winter 2007         SEG2101 - Chapter 1   12
              1.2: Major Principles of
                System Engineering

• Methodology
• Descriptions
• Main descriptions




Winter 2007           SEG2101 - Chapter 1   13
              Methodology (I)

• Systems engineering is performed by a system
  consisting of people and tools called the project
  system or the engineering organization.
• The end results of systems engineering are target
  systems and their documentation, in the form of
  descriptions.
• The role of a systems engineering methodology is
  to help the engineering organization make target
  systems right the first time and every time, within
  budget and on time.
Winter 2007          SEG2101 - Chapter 1            14
              The Role of Methodology




Winter 2007          SEG2101 - Chapter 1   15
              Methodology (II)
• A methodology is made up of a set of methods
  each of which is a systematic way of producing
  some result.
• A methodology prescribes a set of descriptions
  and associated methods.
• Each method provides guidelines for structuring
  and using descriptions in given notations.
• A methodology is a collection of methods that a
  system organization uses to achieve right quality,
  short lead time and low cost.
Winter 2007          SEG2101 - Chapter 1               16
                         Descriptions
              Symbolic representations of the subject matters




Winter 2007                    SEG2101 - Chapter 1              17
              Main Descriptions (I)




Winter 2007          SEG2101 - Chapter 1   18
              Main Descriptions (II)
• Why the system is needed
     – Requirements specification
• What its functionality should be
     – Functional design
• How it should be implemented
     – Implementation design



Winter 2007           SEG2101 - Chapter 1   19
        Requirements Specification
• Clarify the needs of the user and the owner
• Write the needs down as requirements
• The requirements can be clearly understood
  by the user, the owner, and the developer
• Focus on the purpose and role of the system
• Two categories: functional requirements
  and non-functional requirements

Winter 2007       SEG2101 - Chapter 1       20
          Non-Functional Requirements
                                                          Non-functional
                                                           requir ements




                                Product                   Or ganizational                   External
                             requir ements                 requir ements                  requirements




          Ef ficiency         Reliability         Portability        Interoperability        Ethical
         requir ements       requir ements      requirements          requirements        requirements




  Usability                               Delivery        Implementation         Standards         Legislative
requirements                            requirements       requir ements       requirements       requirements




Performance           Space                                                       Privacy            Safety
requirements       requir ements                                               requirements       requirements

     Winter 2007                             SEG2101 - Chapter 1                                     21
              Functional Design
• Define the system functionality as clearly
  and completely as possible
• Define the architecture of the technical
  solution that will be used to realize the
  functionality
• Be represented as functional design and
  implementation design

Winter 2007        SEG2101 - Chapter 1         22
              Implementation Design
• Focuses on the technical solution and its
  relation to the functional design
• Forms the basis of the implementation of
  the concrete system consisting of hardware
  and software
• Tells how the system is going to be realized
• Is derived from the functional design and
  the non-functional requirements
Winter 2007          SEG2101 - Chapter 1     23
              Process Quality
• The conformance between the requirement
  specification and the system.
• Process quality vs system quality




Winter 2007       SEG2101 - Chapter 1       24
              Quality Assurance




Winter 2007     SEG2101 - Chapter 1   25
 Benefits of Systems Engineering (I)
• Step-wise quality assurance can be performed
  during the entire development.
• The user and owner needs are put into focus.
• The functionality can be validated at an early
  stage.
• The number of aspects to be considered at each
  step is reduced.
• The cost of error correction is reduced since error
  can be detected earlier.

Winter 2007          SEG2101 - Chapter 1                26
 Benefits of Systems Engineering (II)
• Different descriptions corresponds to different kinds
  of expert knowledge.
• Language can be selected to fit the specific purpose
  of each description.
• Description can be modified without affecting each
  other.
• The functional design documents the system as whole
  independently of the implementation technology
  chosen for the various parts.
• Each step provides a firm foundation for the next
  step.

 Winter 2007          SEG2101 - Chapter 1           27
     1.3: Managing the System Evolution

• Reference model (waterfall model)
• Documents




Winter 2007       SEG2101 - Chapter 1     28
              Waterfall Model




Winter 2007      SEG2101 - Chapter 1   29
                       Concepts
• Activity: the means of producing results
• Phase: period of time where specific activities are
    carried out and results produced
• Baseline: phase result, basis for future work
• Milestone: phase transition



Winter 2007              SEG2101 - Chapter 1            30
              Milestones and Baselines




Winter 2007          SEG2101 - Chapter 1   31
              Maintenance




Winter 2007        SEG2101 - Chapter 1   32
              Activity Model




Winter 2007     SEG2101 - Chapter 1   33
              Documents




Winter 2007   SEG2101 - Chapter 1   34

				
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