Why Is Software Difficult? · Compiler Format conversion UML-to-XML Good in tightly defined situations IBM Software Group | Rational software Embedded Code in Model Embed code fragments

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IBM Software Group

®

Raising the Level of Development:Models, Architectures, ProgramsDr. James RumbaughIBM Distinguished Engineer

IBM Software Group | Rational software

Why Is Software Difficult?

Business domain and computer have different conceptsApplications require lots of details Code requires internal coordinationLots of repetitious code

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Bridging the Gap

AlignDomain specific language at the top

Abstract Several layers of models with increasing detail

ArchitectSystematic organization for internal details

AutomateUse tools to generate code


Code-Only Development

Deceptively simpleLack of planning leads to trouble

Weak architectureBad decompositionInconsistent formats and interactionsBad for teamworkLots of detailed workBrittle for changes

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Model Driven Architecture (MDA)

Build high-level modelsExpressed in domain concepts

Generate platform-specific codeInto specified architectures

Using automated toolsBased on standards


MDA Approach

Object Management Group (OMG) initiativePlatform Independent Model (PIM)

Captures logic of the application

Implementation profilePlatformTechnology decisions

Platform Specific Models (PSM)Target multiple platformsTranslator incorporates platform knowledge

PIM

PSM

Code

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Needed for MDA

Problem domain modelsUML or domain-specific language (DSL)

Architecture frameworksMake assumptions about infrastructureUse them to remove details from models

Automated toolsModeling toolsRepositoriesTranslators


Needed for MDA

Problem domain modelsArchitecture frameworksAutomated tools

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UML

Build models in UML (Unified Modeling Language)Higher level than programming languagesAdapt UML to application domains with profiles

Special domain concepts Constraints on the use of general UML constructs

UML is still a general-purpose languageMay be a lot of repetitious details


Domain Specific Language (DSL)

Syntax and semantics for a particular purposeReduce conceptual gap

Capture business-level contentMore intuitive syntax

Reduce mindless repetitionPredefined control and data patternsEliminate repetitious control specificationGenerate low-level details

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DSL Examples

yaccUnix compiler-compiler

GUI BuilderVisually construct user interface

Desktop publishing editor (FrameMaker, Word)See the final output while editing

MIDIMusic specification language

MathematicaMathematics notation


SDL

Specification and Description Language (SDL)International Telecommunications Union (ITU) standardSpecial syntax and logic for telephone systemsSDL concepts added to UML 2.0SDL can be modeled as a UML profile

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DSL Styles

DeclarativeSay what to doAvoid control logic

ImperativeSay how to do itExplicit control logic

HybridHigh-level declarativeLow-level imperative


Aspect Oriented Programming (AOP)

Separate different functional aspectsDistinct syntax for each aspectAspects cut across implementation codeExamples: Security, persistence, concurrency, logging

Translator weaves aspects into codexxxxxxx

yyyyyyy

zzzzzzz

aaaaaa

bbbbbb

cccccc

mmmmm

nnnnnnn

ooooooo

xxxxxxx

aaaaaa

mmmmm

yyyyyyy

bbbbbb

Cccccc

nnnnnnn

Ooooooo

Zzzzzzz

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AOP is a Kind of DSL

DSL and AOP depend on good translatorsCurrent AOP languages are awkward

Too much explicit coordination

Expect AOP features from DSL effort


Needed for MDA


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Architecture

Decomposition into subsystemsTopologyInteraction rulesData formatsResource management Hooks for future extensionsScaffolding for testing


Architecture Framework

Framework = reusable architecture patternIncludes:

Skeleton execution environmentPredefined subsystems and topologyInteraction and data rules, formats, interfacesAttachment points for plug-insComponent libraries of useful functionalitySample applications

Implementation development environments (IDE)Eclipse, .NET, J2EE

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Framework Advantages

Enable DSL to eliminate repeated patternsEnsure consistencyExcellent for incremental designEnforce design trade-offs


Specifying Frameworks

UML modelsStructure modelsInteraction modelsInterface modelsPatterns

DSL syntaxCodeText descriptions

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Other Experience-Based Content

PatternsSolution to a common problemParametersDesign, modeling, architecture levelHas structure, interaction rules, trade-offs, guidelines

ComponentsModule ready to plug inHas UML models, code, text descriptions, keywords


Needed for MDA


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Modeling Tools

Build modelsEdit modelsApply patternsOrganize large modelsCoordinate among large teamsCheck for errors and bottlenecks

Generate codeLoad technology and architecture assumptionsTrace generated code to model


Repositories

Standard formatSupport multiple tools and languagesAccess and update modelsMOF (Meta-Object Protocol)XML (Extended Markup Language)

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Translation

Map from DSL and UML to codeUse platform knowledgeOptimize codeReformat to match target languageQuery-View-Transformation (QVT) project to define standard format


Translator Requirements

Understand source and target syntaxGenerated code must be efficient enough

Plenty of experience building good compilers

Support programming language plug-insLots of existing codeHandle unexpected situations

IncrementalMaintain traceabilitySmall change to source small change to target

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Transformation Styles

PartialFullEmbedded code in modelBuilt-up transformation


Partial Transformation

Transform source to codeImplementation details are missingUsually only data structures and code outlines

Then edit the code manuallyGets code stared quicklyFinish the job by programming

Round-trip transformation possibleMaintain traceability linksReverse transformation often ambiguousDifficult to maintain synchronization

Quick way to start using models

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Full Generation

One-way transformation from source to codeGenerate code with all detailsDon’t touch the generated codeHave to anticipate all details in the DSL

CompilerFormat conversion

UML-to-XML

Good in tightly defined situations


Embedded Code in Model

Embed code fragments in the modelWhen DSL is inadequate

Generate code from modelInsert embedded code into generated code

Edit the source model to make changesRegenerate code when neededKeeps the entire specification together

Flexible but mixes levelstransitionT1 () {

ctr = a--;

send (a, b);

}

void methodA () {

return (a + b);

}

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Built-up Transformation

Explicitly model the transformation itselfAssemble out of smaller pieces

Adjust the transformation to change the resultDesign = building a transformation

Source model doesn’t changeReuse on many source models

Can have multiple transformationsPowerful but tricky to build


One-way and Two-way Transformation

One-way—generate source to targetCan’t modify target codeCan insert plug-ins to codeNo synchronization problemsCan add and modify nested code without regeneration

Two-way—round trip engineeringMaintain traceability linksModify source or targetPropagate changes to other modelMuch more difficult to implement

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Executable Models

Allow execution with partial specificationDummy functionsMissing dataUnknown decisions

Incomplete models execute with less detailMay require user guidance

Test architecture earlyAdd detail later


Executable UML

Plain UML is not executablePick action language (built-in actions too primitive)Select semantic variation pointsSupply missing execution semantics

• Tasking, external formats

It is still a general-purpose languageDSLs may be more expressive for most purposes

It may be a useful intermediate formatOutput of DSL mappingsInput to code/platform mappings

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Standards

ModelsArchitecture frameworksCode plug-insEncourage an ecology of vendors

Big vendors: Large generic toolsSmall vendors: Niche-specific plug-insUse plug-ins with generic toolsStandards guarantee access to entire marketExample: Photoshop filters


Status

MDA is still earlyDSLs are still rare but comingGeneric frameworks exist

Domain frameworks will be developed

Transformation technology under developmentQVT standardMuch existing compiler experience

MDA will greatly improve software development

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Documents

Why Is Software Difficult? · Compiler Format conversion UML-to-XML Good in tightly defined situations IBM Software Group | Rational software Embedded Code in Model Embed code fragments