introduction to software construction franco gasperoni gasperoni@adacore.com

Introduction toSoftware Construction

Franco Gasperonigasperoni@adacore.com

http://libre.adacore.com/Software_Matters

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Course Home page

http://libre.adacore.com/Software_Mattershttp://libre.adacore.com/Software_Matters• All the course slides are there (PDF and PowerPoint)All the course slides are there (PDF and PowerPoint)

http://libre.adacore.com/Software_Mattershttp://libre.adacore.com/Software_Matters• All the course slides are there (PDF and PowerPoint)All the course slides are there (PDF and PowerPoint)

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Copyright Notice

© AdaCore under the GNU Free Documentation License

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; provided its original author is mentioned and the link to http://libre.act-europe.fr/ is kept. A copy of the license is included in available at:

http://www.fsf.org/licenses/fdl.html

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Course Objectives

Help you build software Help you build software systems that are more:systems that are more:

• DependableDependable• AdaptableAdaptable• Fun to developFun to develop

Help you build software Help you build software systems that are more:systems that are more:

• DependableDependable• AdaptableAdaptable• Fun to developFun to develop

Comparing ways to Comparing ways to structure softwarestructure software

• Functionality-orientedFunctionality-oriented• Object-orientedObject-oriented• Structural problems with Structural problems with

both approachesboth approaches

Comparing ways to Comparing ways to structure softwarestructure software

• Functionality-orientedFunctionality-oriented• Object-orientedObject-oriented• Structural problems with Structural problems with

both approachesboth approaches

Show problems & pitfalls in Show problems & pitfalls in C-derived languagesC-derived languages

• C, C++, JavaC, C++, Java

Show problems & pitfalls in Show problems & pitfalls in C-derived languagesC-derived languages

• C, C++, JavaC, C++, Java

Show how Ada 95 addresses these issuesShow how Ada 95 addresses these issues• Engineering principles we can take from Ada Engineering principles we can take from Ada

and apply in other languagesand apply in other languages

Show how Ada 95 addresses these issuesShow how Ada 95 addresses these issues• Engineering principles we can take from Ada Engineering principles we can take from Ada

and apply in other languagesand apply in other languages

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Interesting Books

Programming in Ada 95• by John Barnes (Addison Wesley)

High Integrity Ada: The SPARK Approach• by John Barnes (Addison Wesley)

Object-Oriented Software Construction• by Bertrand Meyer (Prentice Hall)

Objects Unencapsulated: Java, Eiffel, and C++• by Ian Joyner (Prentice Hall)

C Traps and Pitfalls• by Andrew Koenig (Addison Wesley)

Effective C++• by Scott Myers (Addison Wesley)

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Course Assumptions

You are interested in the field of software development

You have written computer programs in at least one imperative languages

• E.g. Ada, C, C++, Eiffel, Fortran, Java, Pascal, …

Have a basic knowledge of C• … for the section on problems & pitfalls in C-related languages

Background onSoftware Construction Processes

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Software Development PhasesRequirementsRequirements

What needs to be doneWhat needs to be doneRequirementsRequirements

What needs to be doneWhat needs to be done

AnalysisAnalysisHow it should be doneHow it should be done

AnalysisAnalysisHow it should be doneHow it should be done

DesignDesignCreate a software structure Create a software structure (architecture) around which (architecture) around which code will be built code will be built

DesignDesignCreate a software structure Create a software structure (architecture) around which (architecture) around which code will be built code will be built

CodingCodingFill in the software Fill in the software structure with codestructure with code

CodingCodingFill in the software Fill in the software structure with codestructure with code

TestingTestingCheck that the code does what Check that the code does what it is supposed to (functionality, it is supposed to (functionality, performance, reliability, …)performance, reliability, …)

TestingTestingCheck that the code does what Check that the code does what it is supposed to (functionality, it is supposed to (functionality, performance, reliability, …)performance, reliability, …)

Project ManagementProject ManagementDevise a plan,Devise a plan, manage manage resources, costs, time, …resources, costs, time, …

Project ManagementProject ManagementDevise a plan,Devise a plan, manage manage resources, costs, time, …resources, costs, time, …

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Example of Software Processes

RequirementsRequirementsRequirementsRequirements

AnalysisAnalysisAnalysisAnalysis

DesignDesignDesignDesign

CodingCodingCodingCoding

TestingTestingTestingTesting

Time

RequirementsRequirementsRequirementsRequirements

AnalysisAnalysisAnalysisAnalysis

DesignDesignDesignDesign

CodingCodingCodingCoding

TestingTestingTestingTesting

RequirementsRequirementsRequirementsRequirements

AnalysisAnalysisAnalysisAnalysis

DesignDesignDesignDesign

CodingCodingCodingCoding

TestingTestingTestingTesting

RequirementsRequirementsRequirementsRequirements

AnalysisAnalysisAnalysisAnalysis

DesignDesignDesignDesign

CodingCodingCodingCoding

TestingTestingTestingTesting

Scope (customer needs)

Requirements

Requirements

Analysis

Analysis

Design

Design

Coding

Coding

Testing

Testing

Requirements

Requirements

Analysis

Analysis

Design

Design

Coding

Coding

Testing

Testing

Requirements

Requirements

Analysis

Analysis

Design

Design

Coding

Coding

Testing

Testing

Requirements

Requirements

Analysis

Analysis

Design

Design

Coding

Coding

Testing

Testing

Requirements

Requirements

Analysis

Analysis

Design

Design

Coding

Coding

Testing

Testing

Requirements

Requirements

Analysis

Analysis

Design

Design

Coding

Coding

Testing

Testing

Waterfall Iterative eXtreme Programming (XP)

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Software Phases Related to this Course

DesignDesignCreate a software structure Create a software structure (architecture) around which (architecture) around which code will be built code will be built

DesignDesignCreate a software structure Create a software structure (architecture) around which (architecture) around which code will be built code will be built

CodingCodingFill in the software Fill in the software structure with codestructure with code

CodingCodingFill in the software Fill in the software structure with codestructure with code

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Your Software Development Experience

What is the largest software system that you have built?

How did you build it?• What process?• What programming language?• What tools?• Did you use version control tools?

How long will the software be used for?• Who will fix, change, or adapt the software that you wrote?

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A Small Software System Is …

Understandable by 1 person

Can be thrown away and rewritten to• Repair or extend it• Port it to a new platform

Anything is OK for small systems

The notion of small is programmer-dependent

Typically something less than 10,000 lines of code is small

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A Medium/Large Software System …

Requires a team of people

No single person knows all its aspects

Has a long life-span (> 10 years)

CANNOT throw it away and replace it to• Repair it or extend it• Port it to new platforms

Requires organization, discipline, and the right tools

Software Dependability

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Software Dependability

Degree of user confidence

that the system will operate as expected

and it will not fail in normal use

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The Blue Screen of Death (BSOD)

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Does Software Dependability Matter?

Certainly at the marketing level • No vendor would say its software is undependable• No team would say it produces undependable software

In practice there is plenty of software you cannot depend on

Not all software needs to be dependable

Useful but not very dependable software can be OK • If this machine crashes while doing this presentation I will reboot• If your word processor crashes while you write an important document

there is no harm if you save your document frequently

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Warning about Defect Rates

1 document/year lost while word-processing• Great

2 accidents/month at the International Airport in London

22,000 checks/hour drawn from the wrong account in the US

1 document/year lost while word-processing• Great

2 accidents/month at the International Airport in London

22,000 checks/hour drawn from the wrong account in the US

Is a defect rate of 99.9% acceptable? It depends…

Analyze software defect rates in the context of the applicationAnalyze software defect rates in the context of the application

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Software Failures: Safety

1986: Therac 25 radiation machine kills several patients• Cause: poor testing of the software

June 4, 1996: 1st flight of Ariane 5 aborted: Ariane 5 destroyed

• Cause: Code from Ariane 4 guidance system was reused in Ariane 5 but not tested.

2000: Deadly accident in French highway• Cause: Software malfunction in car braking system. Car manufacturer

acknowledges responsibility.

Software Evolution

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Software Needs to Evolve

Bug Fixes

Port to new architectures• Software lasts for a long time

E.g. Y2K problem• Most useful software outlives the hardware it was designed to run on

E.g. VAX/VMS• When new hardware becomes available it’s cheaper to port existing

applications than rewrite everything from scratch E.g. Intel IA-64

Enhancements & new features• E.g. Dos, Windows 3.1, Windows 95/98/ME, Windows NT/2000/XP

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Software Investment Costs in 2001

Typical software productivity is:• Between 2 and 20 lines of working code (LOC) per programmer per day

Average cost of a programmer per day (loaded with all costs):• Between 150 and 500 USD/day

Average cost to write a line of code (LOC)• Between 10 and 50 USD

Cost to develop a 100,000 LOC application• Typically between 1 M USD to 5 M USD

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Software Evolution is a Must

You cannot just throw away software and redo it• Cost is one thing• But time-to-market is usually even more important

Your software might not need to be very dependable, but…

… it must be capable to evolve• In a timely fashion• At a reasonable cost

Examples• The GNU Ada/C/C++ compiler is over 2 M LOC• Emacs editor is approx 1.4 M LOC• GNU/Linux is approx 4 M LOC

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Software Trend

Software is increasingly developed

by extending and modifying existing systems