Requirements.ppt - Computer Engineering and Information Technology by ewghwehws

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									 The meaning of requirements


 Vahid Jalali
 October 2007



Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 A couple of basic questions

    What is requirement?
          A condition over phenomena of the
           environment
    What is specification?
          Restricted form of requirement
          Providing enough information for the
           implementer


Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Importance of requirements

    Reliance of human beings on
     computer-based systems
    Criticalness and cruciality of these
     computer-based systems




Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Requirements Dos and Does nots

    Do not directly concern machine
    Concern the environment of the
     machine




Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Shared Phenomena

    Common phenomena between
     machine and environment
          Controlled by machine
          Controlled by environment
    Used as a bridge between machine
     and private phenomena


Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
  Affecting private phenomena

                                             Shared Phenomena
                    Direct
Machine
                                                      Direct
                    Indirect



                                                    Private Phenomena

 Amirkabir university of technology, Department of computer engineering and
 information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
 Requirement engineering course, Fall 2007
 Optative and Indicative

    Describing a requirement
          Desired condition over the phenomena
           of the environment
          Given properties of the environment
           regarding shared phenomena




Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Optative and Indicative (Cont.)
    Optative : A customer requirement R
     expresses a condition over the
     phenomena of the environment that we
     wish to make true by installing the
     machine
    Indicative : An environment assertion E
     expresses a condition over the
     phenomena of the environment that we
     know to be true irrespective of the
     properties and behavior of the machine
Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Optative and Indicative (Cont.)
    Distinction between optative and
     indicative
          Is time independent
          The environment properties that guaranteed
           by the environment itself are indicative
          The environment properties that are to be
           guaranteed by the machine are optative
          Is also applicable to description of an agent



Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Requirement engineering

    Which kind of description to regard,
     optative or indicative?
          Actually both of them
    Reasons for regarding indicative
     descriptions in addition to optative
     ones
          Understanding the environment
          Assuring satisfiablity of requirements
Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Assuring satisfiablity
    A couple of conditions should hold
          a machine whose behavior satisfies S is
           installed in the environment
          Environment has the properties described
           in E




Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Formalism

    Elevate the accuracy of descriptions
    Computer can be treated as a
     formal system
    Environment on contrast can not
    Formalism impels no extra
     constraints on environment
    Formalism can be met through
     using ground terms in a description
Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Ground terms

    Have clear and unambiguous
     meaning
    Fix relationship between description
     and what it describes
    Are captured by a tool named
     designation


Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Designation
    A designation associates a formal ground
     term, such as a predicate, with the
     denoted phenomena, such as an event or
     entity class or a relationship over events
     or entities
    Appropriately chosen and carefully written
     designations provide a strong and narrow
     bridge between the environment and its
     description in requirements

Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Designation (Cont.)
    define the scope of a requirement
    clarify the meaning of the descriptions
    allow these descriptions to be subjected
     to the test of falsifiability
    allow us to reason more reliably about the
     environment
    Convince satisfaction of our specification
     will guarantee satisfaction of the
     requirements
Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Designation Vs definition
    Both underpin an essential
     discipline in description
    Every term used in every
     description must be either
     designated or defined
    Definition defines new terms on the
     basis of terms previously
     designated or previously formally
     defined
Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Designation Vs definition (Cont.)

    Definition provides more convenient
     terminology for saying what we
     could have said less conveniently




Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007
 Reference

    [1]. M.Jackson, “The meaning of
     requirements,” Annals of Software
     Engineering Special Issue on
     Software Requirements Engineering




Amirkabir university of technology, Department of computer engineering and
information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab,
Requirement engineering course, Fall 2007

								
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