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Transcript of schach5-chap05-14[1]
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Slide 5.1
The McGraw-Hill Companies, 2002
Object-Oriented and Classical Software
Engineering
Fifth Edition, WCB/McGraw-Hill, 2002
Stephen R. [email protected]
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Slide 5.2
The McGraw-Hill Companies, 2002
CHAPTER 5
THE TOOLSOF THE TRADE
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Slide 5.3
The McGraw-Hill Companies, 2002
Overview
q Stepwise refinementq Costbenefit analysisq Software metricsq CASEq Taxonomy of CASEq Scope of CASEq Software versionsq Configuration controlq Build tools
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Slide 5.4
The McGraw-Hill Companies, 2002
Stepwise Refinement
q A basic principle underlying many softwareengineering techniques Postpone decisions as to details as late as possible
to be able to concentrate on the important issuesq Millers law (1956)
A human being can concentrate on 72 items at atime
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Slide 5.5
The McGraw-Hill Companies, 2002
Stepwise Refinement Case Study
q Design a product to update a sequential master file containing name and address data for monthly magazine True Life Software Disasters
q Three types of transactions Type 1: INSERT (new subscriber into master file) Type 2: MODIFY (existing subscriber record) Type 3: DELETE (existing subscriber record)
q Transactions are sorted into alphabetical order,and by transaction code within alphabeticalorder
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Slide 5.6
The McGraw-Hill Companies, 2002
Typical file of input transactions
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Slide 5.7
The McGraw-Hill Companies, 2002
Decompose Process
q No further refinement is possible
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Slide 5.8
The McGraw-Hill Companies, 2002
First Refinement
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Slide 5.9
The McGraw-Hill Companies, 2002
Stepwise Refinement Case Study (contd)
q Assumption We can produce a record when PROCESS requires it
q Separate INPUT and OUTPUT, concentrate onPROCESS
q What is this PROCESS?
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Slide 5.10
The McGraw-Hill Companies, 2002
Second Refinement
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Slide 5.11
The McGraw-Hill Companies, 2002
Third Refinement
q This designhas a major fault
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Slide 5.12
The McGraw-Hill Companies, 2002
Stepwise Refinement Case Study (contd)
q The third refinement is WRONG Modify JONES followed by Delete JONES
q After the third refinement has been corrected Details like opening and closing files have been ignored
up to now Fix after the logic of the design is complete The stage at which an item is handled is vital
q Opening and closing files is Ignored in early steps, but Essential later
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Slide 5.13
The McGraw-Hill Companies, 2002
Appraisal of Stepwise Refinement
q A basic principle used in Every phase Every representation
q The power of stepwise refinement
The software engineer can concentrateon the relevant aspects
q Warning Millers Law is a fundamental restriction
on the mental powers of human beings
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Slide 5.14
The McGraw-Hill Companies, 2002
CostBenefit Analysis
q Compare estimated future benefits, costs Estimate costs Estimate benefits State all assumptions explicitly
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Slide 5.15
The McGraw-Hill Companies, 2002
CASE (Computer-Aided Software Engineering)
q Scope of CASE Can support the entire life-cycle
q Graphical display tools (many for PCs) Data flow diagrams
Entity-relationship diagrams Module-interconnection diagrams Petri nets Structure charts
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Slide 5.16
The McGraw-Hill Companies, 2002
Software Metrics
q To detect problems early, it is essential tomeasure
q Examples: LOC per month Defects per 1000 lines of code
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Slide 5.17
The McGraw-Hill Companies, 2002
Different Types of Metrics
q Product Metrics Examples:
Size of product Reliability of product
q Process Metrics Example:
Efficiency of fault detection duringdevelopment
q Metrics specific to a given phase
Example: Number of defects detected per hour inspecification reviews
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Slide 5.18
The McGraw-Hill Companies, 2002
The Five Basic Metrics
q Size In Lines of Code, or better
q Cost In dollars
q Duration In months
q Effort
In person monthsq Quality Number of faults detected
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Slide 5.19
The McGraw-Hill Companies, 2002
Taxonomy of CASE
q UpperCASE versus lowerCASE
q Tool versus workbench versus environment
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Slide 5.20
The McGraw-Hill Companies, 2002
Graphical Tool
q Additional features Data dictionary Screen and report generators Consistency checker; the various
views are always consistent Specifications and design workbench
q Online Documentation Problems with
Manuals
Updatingq Essential online documentation
Help information Programming standards
Manuals
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Slide 5.21
The McGraw-Hill Companies, 2002
Essential Coding Tools
q Coding tools Products (such as text editors, debuggers, and
pretty printers) designed to Simplify programmers task Reduce frustration Increase programmer productivity
q Conventional coding scenario for programming-in-the-small Editor-compiler cycle
Editor-compiler-linker cycle Editor-compiler-linker-execute cycleq There must be a better way
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Slide 5.22
The McGraw-Hill Companies, 2002
Syntax-directed Editor
q Understands language Speeds up implementation User interface of an editor is different to that of a compile
There is no need to change thinking mode No mental energy is wasted on these adjustments
One piece of system software, two languages High-level language of module Editing command language
Pretty-printer
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Slide 5.23
The McGraw-Hill Companies, 2002
Online Interface Checker
q Example The programmer tries to call procedure
computeAverage , but the linker cannot find it The programmer realizes that the actual name
of the procedure is computeMean
q A structure editor must support onlineinterface checking Editor must know name of every procedure
q Interface checking is an important part of programming-in-the-large
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Slide 5.24
The McGraw-Hill Companies, 2002
Online Interface Checker (contd)
q Example The user enters the call
average = computeAverage (dataArray, numberOfValues);
Editor immediately responds with a message such asProcedure computeAverage not known
q Programmer is given two choices Correct the name of the procedure Declare new procedure computeAverage and specify
its parametersq Enables full interface checking
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Slide 5.25
The McGraw-Hill Companies, 2002
Online Interface Checker (contd)
q Example Declaration of q is
void q ( float floatVar, int intVar, String s1, String s2);
Call (invocation) isq (intVar, floatVar, s1, s2);
Online interface checker detects the faultq Help facility
Online information as to parameters of method q
Better: Editor generates a template for the call Shows type of each parameter Programmer replaces formal by actual parameter
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Slide 5.26
The McGraw-Hill Companies, 2002
Online Interface Checker (contd)
q Advantages No need for different tools with different interfaces Hard-to-detect faults are immediately flagged for
correction Wrong number of parameters Parameters of wrong type
q Essential when software is produced by a team If one programmer changes the interface specification,
all modules calling that changed module must bedisabled
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Slide 5.27
The McGraw-Hill Companies, 2002
Online Interface Checker (contd)
q Remaining problem The programmer still has to exit from the editor to
invoke the compiler (to generate code) Then, the linker must be called to link the product Must adjust to the JCL, compiler, and linker output
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Slide 5.28
The McGraw-Hill Companies, 2002
Operating System Front-End in Editor
q Single command go or run Use of the mouse to choose icon, or menu
selectionq
Causes editor to invoke the compiler, linker,loader, and execute the product
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Slide 5.29
The McGraw-Hill Companies, 2002
Operating System Front-End in Editor (contd)
q Online documentation Help information regarding
Operating system Editor Programming language
Programming standards Manuals
Editor manuals Programming manuals
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Slide 5.30
The McGraw-Hill Companies, 2002
Source Level Debugger
q Example: Product executes terminates abruptly and prints
Overflow at 4B06 , or Core dumped , or Segmentation fault
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Slide 5.31
The McGraw-Hill Companies, 2002
Source Level Debugger (contd)
q The programmer works in a high-level language,but must examine Machine code core dumps Assembler listings
Linker listings Similar low-level documentationq Destroys the advantage of programming in a
high-level languageq We need
Interactive source level debugger (like dbx )
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Slide 5.32
The McGraw-Hill Companies, 2002
Programming Workbench
q Structure editor with Online interface checking capabilities Operating system front-end Online documentation Source level debugger
q Constitutes a simple programming environment
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Slide 5.33
The McGraw-Hill Companies, 2002
Programming Workbench (contd)
q This is by no means new All the above features are supported by FLOW (1980) The technology has been in place for years
q Surprisingly, some programmers still implement
code Ye Olde-Fashioned Way
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Slide 5.34
The McGraw-Hill Companies, 2002
Software Versions
q During maintenance, at all times there are atleast two versions of the product: The old version, and The new version
q
Two types of versions: revisions and variations
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Slide 5.35
The McGraw-Hill Companies, 2002
Revisions and Variations
q Revision Version to fix a fault in the module We cannot throw away an incorrect version
q Perfective and adaptive maintenance alsoresults in revisions
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Slide 5.36
The McGraw-Hill Companies, 2002
Revisions and Variations (contd)
q Variation Version for different operating systemhardware Variations are designed to coexist in parallel
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Slide 5.37
The McGraw-Hill Companies, 2002
Configuration Control
q Every moduleexists in threeforms Source code;
object code;executable loadimage
q Configuration
Version of eachmodule fromwhich a givenversion of aproduct is built
l l
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Slide 5.38
The McGraw-Hill Companies, 2002
Version Control Tool
q Essential for programming-in-the-many First step toward configuration management
q Must handle Updates
Parallel versions
l l ( d)
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Slide 5.39
The McGraw-Hill Companies, 2002
Version Control Tool (contd)
q Possible notation printerDriver (laser) / 13 printerDriver (inkJet) / 25
q Problem of multiple variations Deltas
q Version control is not enoughmaintenance issue
C fi i C l d M i
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Slide 5.40
The McGraw-Hill Companies, 2002
Configuration Control and Maintenance
q Two programmers working on the same module mDual / 16 mDual / 17
q Baselines Private workspaces Freezing
q Configuration control during development Informal testing
SQA
B ild T l
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Slide 5.41
The McGraw-Hill Companies, 2002
Build Tools
q Example UNIX make
q Compares the date and time stamp on Source code, object code
Object code, executable load imageq Can check dependencies
Ensures that correct versions/variations arecompiled and linked
P d i i G i i h CASE T l
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Slide 5.42Productivity Gains with CASE Tools
q Survey of 45 companies in 10 industries[Myers, 1992] Half information systems Quarter scientific Quarter real-time aerospace
q Results About 10% annual productivity gains $125,000 per seat
q Justifications for CASE Faster development Fewer faults Easier maintenance Improved morale
