Software System Engineering: A Tutorial

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Software System Engineering A Tutorial

• Richard H. Thayer, Ph.D.
• Life Fellow, IEEE
• California State University, Sacramento

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What is a System?

• A system is a collection of elements related in a
  way that allows the accomplishment of a common
  object
• A man-made system is a collection of hardware,
  software, people, facilities, procedures, and
  other factors organized to accomplish a common
  objective.

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Software System

• A man-made system consisting of a collection of
  programs and documents that work together,
  creating a set of requirements with the specified
  software

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What is System Engineering?

• Definition
• Practical application of scientific, engineering,
  and management skills necessary to transform a
  users need into a system configuration
  description that most effectively and efficiently
  satisfies the need. SE produces documents, not
  artifacts

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System Engineering (SE)

• Overall technical management of a
  system-development project
• Problem solving process that provides mechanisms
  for identifying and evolving the product and
  process definitions of a system
• Establishes a technical development management
  plan for the project
• Provides the baseline for all software and
  hardware development

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Functions of SE

• Problem Definition
• Determines the needs and constraints through
  analysis of requirements and interfacing with the
  acquirer
• Solution Analysis
• Determines the set of possible ways to satisfy
  requirements and constraints, studies and
  analyzes possible solutions, and selects the
  optimum one
• Process Planning
• Determines the tasks to be done, project size and
  effort required to develop the product,
  precedence among tasks, and potential risks to
  the project
• Process Control
• Determines the methods for controlling the
  project and the process, measures progress,
  reviews intermediate products, and takes
  corrective action when necessary
• Product Evaluation
• Determines the quality and quantity of the
  delivered product through evaluation planning,
  testing, demonstration, analysis, examination,
  and inspection

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What is Software System Engineering (SwSE)?

• Both a
• Technical Process
• Management Process
• Performed by
• System engineers
• Managers
• Software engineers
• Programmers
• Acquirers
• Users

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Why software requires system engineering

• System engineering defines a solution space
• Solution space defines system boundaries and its
  interfaces with outside systems
• SE defines the product solution of the highest
  level

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Why is SwSE necessary?

• Responsible for the overall technical management
  of the system and the verification of the final
  system products

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Software Engr. w/o SE

• Complex software systems become unmanageable
• Costs are overrun and deadlines are missed
• Unacceptable risks are sometimes taken, leading
  to greater risk exposure
• Erroneous decisions are made early in the life
  cycle and prove very costly in the end
• Independently developed subsystems and components
  do not integrate properly
• Parts and components are not built or
  requirements are not met
• The delivered system fails to work properly
• Parts of the system must be reworked after
  delivery

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What is software engineering?

• The practical application of computer science,
  management, and other sciences to the analysis,
  design, construction, and maintenance of software
  and its associated documentation
• An engineering science that applies the concepts
  of analysis, design, coding, testing,
  documentation, and management to be successful
  completion of large, custom-built computer
  programs under time and budget constraints
• The systematic application of methods, tools, and
  techniques to achieve a stated requirement or
  objective for an effective and efficient software
  system

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What is project management?

• Involves assessing the software systems risks
  and costs, establishing a master schedule,
  integrating the various engineering specialties
  and design groups, maintaining configuration
  control, and continuously auditing the effort to
  ensure that cost and schedule are met and
  technical requirements objectives are satisfied

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Functions of SwSE

• Requirements Analysis
• Determines the needs and constraints of the
  software system by analyzing the system
  requirements that have been allocated to software
• Software Design
• Determines the set of possible ways to satisfy
  the software requirements and constraints,
  studies and analyzes the possible solutions, and
  selects, and selects the optimum one
• Process Planning
• Determines the tasks to be done, the project
  size, the effort necessary to develop the
  product, the precedence between tasks, and the
  potential risks to the project
• Process Control
• Determines the methods for controlling the
  project and the process, measures progress,
  reviews intermediate products, and takes
  corrective action when necessary
• Verification, Validation, Testing
• Evaluates the final product and documentation
  through testing, demonstrations, analysis, and
  inspections

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Recall SE vs. SwSE

• SE
• Problem Definition
• Solution Analysis
• Process Planning
• Process Control
• Product Evaluation

• SwSE
• Requirements Analysis
• Software Design
• Process Planning
• Process Control
• Verification, Validation, Testing

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SwSE Requirements Analysis

• Definition
• A software capability needed by a user to solve a
  problem or achieve an objective
• A system capability that must be met or possessed
  by a software system of software system component
  to satisfy a contract, standard, specification,
  or other formally imposed document

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SwSE Requirements Analysis

• Establishes
• Functional Requirements
• Specifies functions that a system of system
  component must be able to perform
• Performance Requirements
• Specifies performance characteristics that a
  system or system component must possess
• External Interface Requirements
• Specifies hardware, software, or database
  elements with which a system or system component
  must interface, or setting forth constraints on
  formats, timing, or other factors caused by such
  an interface
• Design constraint Requirements
• Affects of constrains the design of a software
  system or software system component
• Quality Attribute Requirements
• Specifies the degree to which software possesses
  attributes that affect quality, such as
  correctness, reliability, maintainability, and
  portability

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SwSE Requirements Analysis (contd)

• Initiated
• Acquirer and user system requirements have been
  properly identified
• A top-level system design is complete
• A set of software subsystems is identified
• All user requirements have been properly
  allocated to one of more of these subsystems
• Complete
• A ConOps document is complete
• All of the software system requirements is
  identified
• An SRS that identifies what the system must do
  is written
• SRS is verified
• A requirements tracing is complete
• A preliminary user manual is written
• A test compliance matrix is finished
• A preliminary test specification is finished
• The software specification review is complete
• A requirements baseline is established

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SwSE Software Design

• Definition
• Process of selecting and documenting the most
  effective and efficient system elements that
  together will implement the software system
  requirements
• Two types
• Architectural
• Detail

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SwSE Architectural Design

• Establishes
• Top-level system design
• General system structure
• System components that populate the architecture
• General description of each subsystem
• Source of each subsystem
• Internal interfaces between subsystems
• External interfaces with outside systems
• Allocation of the functional requirements to the
  subsystems
• Allocation of nonfunctional requirements to each
  subsystem
• Verification that the architectural subsystem
  implements the requirements specifications

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SwSE Software Design (contd)

• Initiated
• The software requirements have been properly
  identified and documented
• The draft users manual and draft test documents
  have been developed
• Completed
• The how question is answered
• The architectural description is complete
• An architectural design review is complete, and
  the stakeholders have accepted the design
  description
• The preliminary operators and maintenance
  manuals are written
• The design tracing is complete
• The architectural design is reviewed
• The architectural design is verified
• The product baseline is established

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SwSE Process Planning

• Planning the engineering workload
• Work done by PM
• Work done by SW Engr.
• Determine tasks to be done
• Work breakdown structure (WBS) represents
  hierarchically the parts of a process or product
• Determine project effort and schedule
• Determine technical and managerial risks
• Schedule overrun
• Exceeding budget
• Delivering an unsuitable product

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SwSE Process Control

• Control
• collection of management activities used to
  ensure that the project goes according to plan
• Process Control
• feedback system that provides information on how
  well the project is going.
• Asks questions
• Are there potential problems that will impact the
  budget/schedule?
• Have any of the risks turned to problems?
• Is the design approach still doable?

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SwSE Process Control (contd)

• Control the engineering workload
• Control done by the PM
• Control done by the SW Engr.
• Develop standards of performance
• Set of procedures that define the process for
  developing a software product and/or specify the
  quality of a software product
• Establish monitoring and reporting systems
• SQA Planned pattern of actions that provide
  confidence that the product conforms to
  established technical requirements
• SCM Method of controlling reporting software
  status
• Measure results
• Walkthroughs
• Independent Auditing
• Take corrective action if process fails to meet
  plan standard

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SwSE Verification, Validation, Testing

• Definition
• Determine that the engineering process is correct
  and the products are in compliance with their
  requirements

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SwSE VV T

• Verification
• Am I building the product right
• Validation
• Am I building the right product
• Testing
• Usual considered part of validation

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SwSE VV T (contd)

• Initiated
• The software is complete
• Unit tests are complete
• Completed
• Software integration testing is complete
• Software system testing is complete

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SwSE Software Integration Testing

• Incremental
• Top-down
• Use of stubs
• Bottom-up
• Use of drivers
• Non-incremental

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Conclusion

• SE SwSE are disciplines used in the front end
  of the system life cycle for technical planning
  and at the latter part of the life cycle to
  verify whether the plans have been met

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Questions??