software engineering principles · requirement analysis and specification design and specification...

Importance of PrinciplesKey Principles

Case Study

Software Engineering Principles

Miaoqing HuangUniversity of Arkansas

Spring 2010

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Case Study

Outline

1 Importance of Principles

2 Key Principles

3 Case StudyCompiler Construction

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Case Study

Outline


2 Key Principles


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Case Study

Principles, Methodologies, and Tools

Principles primarily deal with the process of softwareengineering, i.e., the development of software

The right process will help produce the desired software productPrinciples will guide the adoption of methodologies and the tools

Methodologies and tools change more frequently than principles

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Case Study

Principles, Methodologies, and ToolsExample

How can we fly?Principle: fight against the gravity

Hot air is lighter than cold airBuoyancy (lift-up force) >Gravity (drag-down force)

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Case Study

Principles, Methodologies, and ToolsExample

How can we fly?Principle: fight against the gravity

1 Air is diverted down fromwings

2 Air pushes backNewton’s third law

3 The airplane is lifted up intothe sky

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Case Study

Outline


2 Key Principles


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Case Study

Key Principles

1 Rigor and formality2 Separation of concerns3 Modularity4 Incrementality5 Abstraction6 Generality7 Anticipation of change

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Case Study

Rigor and Formality

Software Engineering must be practiced systematicallyRigor is a necessary complement to creativity that increases ourconfidence in our developments

Computer is not the same as human, i.e., it is not able to handlevague commands

Formality is rigor at the highest degreeSoftware process is driven and evaluated by mathematical laws

Examples:Mathematical (formal) analysis of program correctnessSystematic (rigorous) test data derivationRigorous documentation of development steps helps projectmanagement and assessment of timeliness

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Case Study

Separation of Concerns, Modularity

Separation of ConcernsSeparate the complexities and concentrate on one at a time

“Divide and conquer”Example: keep product requirement separate, i.e., functionality,performance, usability

Support parallelization of efforts and separation ofresponsibilities

Modularity: the cornerstone principleA complex system may be divided into simpler pieces calledmodulesA system that is composed of modules is called modularSupport application of separation of concerns

When dealing with a module we can ignore details of othermodules

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Case Study

ModularityCohesion and Coupling

High coupling Low coupling

Law of DemeterEach unit should only talk to its friends; don’t talk to strangersThe resulting software tends to be more maintainable andadaptable

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Case Study

ModularityTop-down and bottom-up

Top-downDecompose the whole design into modules first and thenconcentrate on individual module design

Bottom-upConcentrate on modules and then on their composition

They are two phases of the whole design process

Requirement analysisand specification

Design and specification

Code and module testing

Integration and system testing

Delivery and maintenance

Top-down

Bottom-up

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Case Study

Incrementality

Process proceeds in a stepwise fashion (increments)Deliver subsets of a system (prototype) early to get early feedbackfrom expected users, then add new features incrementallyDeal first with functionality, then turn to performance

First step: quick-and-dirty solutionSecond step: more efficient (i.e., cleaner) design

Example: Game DesignFirst 2-D release then work on 3-D designFirst coarse-grained texture then fine-grained texture

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Case Study

Abstraction

Identify the important aspects of a phenomenon and ignore itsdetailsSpecial case of separation of concernsThe type of abstraction to apply depends on purpose or roles(user or designer)

The user of a software concerns the what it does, not how it doesThe designer in a team concerns what and how of his/her ownpart, and what of other parts that belong to other team members

After a module is fully tested and verified, only the what part isconcerned by its user

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Case Study

Generality

Discover if it is an instance of a more general problem whosesolution can be reused in other cases

Increase the reusabilityCarefully balance generality against performance and cost

The solution to a generalized problem most likely is moreexpensive than the solution to a special problem

A program that can handle the multiplication between two generalmatricesA program that is specially designed to handle the multiplicationbetween two sparse matrices

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Case Study

Anticipation of Change

Ability to support software evolution requires anticipatingpotential future changes

Minimize the changes to the existing moduleLeave the spots in the program for future features

Basis for software evolvabilityExample

A sorting program based on array of fixed lengthA sorting program based on link of dynamic length

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Case StudyCompiler Construction

Outline


2 Key Principles


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The modular structure of a compiler

Lexicalanalysis

ParsingCode

GenerationSourcecode

“Tokenized”code

Parsetree

Objectcode

Symbol table

Syntax diagnosticsLexical diagnostics

Code Generation

Intermediatecode generation

Machine codegeneration

Intermediatecode

Objectcode

Parsetree

Symbol table

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Principles breakdown

Rigor and formalityCompiler design is one of the most serious business in softwaredevelopment

Separation of concerns, modularity, and incrementalityCorrectness first, performance next, then ease of useDecompose the whole project into small modules that can bedesigned and verified in a comparatively easy wayCover only a subset of the source language and omit somefeatures in the first release

Abstraction and generalityGenerate intermediate code for an abstract machine

Java Virtual machineUse command-line arguments to specify the target machine

gcc or g++ compiler

Anticipation of changeNew instruction set with new processor architecture

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software engineering principles · requirement analysis and specification design and specification...

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