Software Engineering Principles

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Software Engineering Principles

• CSC 2110 - Data Structures Abstraction
• Spring/Summer 2001
• Wayne State University
• Instructor Anne-Marie Bosneag

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Content

• The software life cycle
• Goals of quality software
• Functional object-oriented design
• Software verification
• Detecting and solving different types of errors

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Programming Life Cycle Activities

• Problem analysis understand the problem
• Requirements definition specify what
  program will do
• High- and low-level design how it meets
  requirements
• Implementation of design code it
• Testing and verification detect errors, show
  correct
• Delivery turn over to customer
• Operation use the program
• Maintenance change the program

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Software Engineering

• A disciplined approach to the design, production,
  and maintenance of computer programs that are
  developed on time and within cost estimates,
  using tools that help to manage the size and
  complexity of the resulting software products.

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An Algorithm Is . . .

• A logical sequence of discrete steps that
  describes a complete solution to a given problem
  computable in a finite amount of time.

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Goals of Quality Software

• It works.
• It can be read and understood.
• It can be modified.
• It is completed on time and within budget.

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Detailed Program Specification

• Tells what the program must do, but not how it
  does it.
• Is written documentation about the program.

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Detailed Program Specification Includes

• Inputs
• Outputs
• Processing requirements
• Assumptions

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Abstraction

• A model of a complex system that includes only
  the details essential to the perspective of the
  viewer of the system.

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Information Hiding

• Hiding the details of a function or data
  structure with the goal of controlling access to
  the details of a module or structure.
• PURPOSE To prevent high-level designs from
  depending on low-level design details that may be
  changed.

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Two Approaches to Building Manageable Modules
OBJECT-ORIENTED DESIGN

• FUNCTIONALDECOMPOSITION

FOCUS ON processes FOCUS ON data
objects
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Functional Design Modules
Main
Get Data
Prepare File for Reading
Print Data
Print Heading
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Object-Oriented Design
A technique for developing a program in which the
solution is expressed in terms of objects --
self- contained entities composed of data and
operations on that data.
ltlt
gtgt
setf
get
Private data
Private data
. . .
. . .
ignore
cout
cin
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More about OOD

• Languages supporting OOD include C, Java,
  Smalltalk, Eiffel, and Object-Pascal.
• A class is a programmer-defined data type and
  objects are variables of that type.
• In C, cin is an object of a data type (class)
  named istream, and cout is an object of a class
  ostream. Header files iostream and fstream
  contain definitions of stream classes.

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Procedural vs. Object-Oriented Code

• Read the specification of the software you
  want to build. Underline the verbs if you are
  after procedural code, the nouns if you aim for
  an object-oriented program.
• Grady Booch, What is and Isnt Object
  Oriented Design, 1989.

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Program Verification

• Program Verification is the process of
  determining the degree to which a software
  product fulfills its specifications.

SPECIFICATIONS Inputs
Outputs Processing
Requirements Assumptions
PROGRAM
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Verification vs. Validation

• Program verification asks,
• Are we doing the job right?
• Program validation asks,
• Are we doing the right job?
• B. W. Boehm, Software Engineering
  Economics, 1981.

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Program Testing

• Testing is the process of executing a program
  with various data sets designed to discover
  errors.

DATA SET 4 . . .
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Various Types of Errors

• Design errors occur when specifications are wrong
  
• Compile errors occur when syntax is wrong
• Run-time errors result from incorrect
  assumptions, incomplete understanding of the
  programming language, or unanticipated user
  errors.

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Robustness

• Robustness is the ability of a program to recover
  following an error the ability of a program to
  continue to operate within its environment.

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An Assertion

• Is a logical proposition that is either true or
  false (not necessarily in C code).
• EXAMPLES
• studentCount is greater than 0
• sum is assigned count gt 0
• response has value y or n
• partNumber 5467

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Preconditions and Postconditions

• The precondition is an assertion describing what
  a function requires to be true before beginning
  execution.
• The postcondition describes what must be true at
  the moment the function finishes execution.
• The caller is responsible for ensuring the
  precondition, and the function code must ensure
  the postcondition.

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Example

• void PrintList ( ofstream dataFile,
  UnsortedType list)
• // Pre list has been initialized.
• // dataFile is open for writing.
• // Post Each component in list has been
  written to dataFile.
• // dataFile is still open.
• int length
• ItemType item
• list.ResetList()
• length list.LengthIs()
• for (int counter 1 counter lt length
  counter)
• list.GetNextItem(item)
• item.Print(dataFile)

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A Walk-Through

• Is a verification method using a team to perform
  a manual simulation of the program or design,
  using sample test inputs, and keeping track of
  the programs data by hand.
• Its purpose is to stimulate discussion about the
  programmers design or implementation .

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Tasks within each test case

• determine inputs that demonstrate the goal.
• determine the expected behavior for the input.
• run the program and observe results.
• compare expected behavior and actual behavior.
  If they differ, we begin debugging.

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Integration Testing

• Is performed to integrate program modules that
  have already been independently unit tested.

Main
Get Data
Print Weighted Average
Prepare File for Reading
Find Weighted Average
Print Data
Print Heading
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Integration Testing Approaches
BOTTOM-UP

• TOP-DOWN

Ensures individual modules work together
correctly, beginning with the lowest level.
Ensures correct overall design logic.
USES placeholder USES a test
driver to call module stubs to test
the functions being tested. the order of
calls.