The role of OCL in theModel Driven Architecture

Jos Warmer

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J.Warmer@klasse.nl

http://www.klasse.nl

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Part 1

The role of modeling in software development.

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Modeling Maturity Levels

MML 0: No specification

MML 1: Textual Specification

MML 2: Text with Models

MML 3: Models with Text

MML 4: Precise Models

MML 5: Models only

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MML 0: No Specification

Specification of software is kept in the heads of the developers.

My software

…

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MML 1: Textual

Specification of software is written down in one or more natural language documents.

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MML 2: Text with Diagrams

Specification of software in one or more natural language documents…

… plus several high-level diagrams to explain the overall architecture.

+

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MML 3: Models with Text

Specification of software is written down in one or more models.

Additional natural language text is used to explain the background and motivation of the models.

+

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MML 4: Precise Models

Specification of software is written down in one or more models.– Natural language text is used to explain the

background and motivation of the models.

The models are precise enough to have a direct link with the actual code.

This is what the OMG calls MDA or Model Driven architecture.

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MML 5: Models Only

The models are precise and detailed enough to allow complete code-generation.

The code is invisible (as assembler is today).

Modeling language High level programming language.

This is future technology ().

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UML in the MMLs

MML 0: No use of UML

MML 1: No use of UML

MML 2: Moderate use of UML

MML 3: Extensive use of UML

MML 4: Extensive use of UML with OCL

MML 5: ???

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MDA and MML

OMG’s Model Driven Architecture is designed for MML level 4

– Ultimate goal is level 5

UML and OCL play an important role

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MDA Overview

Automatic transformation from platform independent model (PIM) to platform specific models (PSM).– PIM usually written in UML.– PSM can be diverse:

• Java, J2EE, SQL, C++, .NET, COBOL, C#, CORBA, XML, etc. etc.

– Bridges between PSMs generated as well.

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MDA Example

SQL - EJB EJB - JSP

Platform Independent Model

PSM JSPPSM SQL PSM EJB

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Experience in moving to MDA

Companies moving from MML 3 to MML 4 (MDA) realize the need for OCL and are using it.

Tools vendors developing tools for MDA realize the same and add support for OCL (e.g. ArcStyler, OptimalJ).

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Part 2: OCL

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Object Constraint Language

OCL is about objects

OCL is a language

OCL is not just about constraints

OCL is the UML

expression / query language

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History of OCL

Syntropy influenced by Z

Language for Business Modeling

IBM/ObjecTime OMG submission

Part of UML standard

Extended and formally defined for UML 2.0

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OCL Characteristics

Ease-of-use– Readable and writeable by wide audience

Pure expression language– Side-effect free

Specification language– Declarative and platform independent

Precision– Unambiguous, formal (?)

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Example Model

Bottlecapacity : Integercontents : Integerweight : Integerdiameter : IntegerneckDiameter : Integer

totalWeight() : Integer

CapinnerDiameter : Integerweight : Integer

0..1

cap

0..*

bottles

Cratecapacity : IntegermaxWeight : IntegermaxDiameter : Integer

totalWeight() : IntegeraddBottle(b : Bottle)

0..1bottle

0..1

Palletcapacity : IntegermaxWeight : Integer

totalWeight() : IntegeraddCrate(c : Crate)

0..1

crates0..*

pallet

crate

0..*

/ caps

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Invariants on Classes

context Crate

-- the number of bottles may not exceed its capacity

inv: bottles->size() <= capacity

-- each bottle must fit in the crateinv: bottles->forAll(diameter < maxDiameter)

-- the total weight must be less than the maximuminv: totalWeight() <= maxWeight

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Invariants on Classes

context Crate

-- each bottle must fit in the crateinv: bottles->forAll(diameter < maxDiameter)

FORALL b : Bottle FROM bottlesISTRUE b.diameter < maxDiameter

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State invariants

context Bottle

state Closed inv: contents = capacity

open

closed

Bottle capacity : Integer contents : Integer weight : Integer diameter : Integer neckDiameter : Integer

totalWeight() : Integer

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Design by Contract

Pre- and post-conditions

Takes “Design by Contract” principle into “Analysis by Contract”

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Preconditions on Operations

context Crate::addBottle( b : Bottle )

-- there must be room in the crate

pre: bottles->size() < capacity

-- the maximum weight for the crate may not be exceeded

pre: totalWeight() + b.totalWeight() <= maxWeight

-- the bottle is not in the crate

pre: not bottles->includes( b )

-- ‘b’ is added to the collection of bottlespost: bottles = bottles@pre->including(b)

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Use Case Pre/Postcondtions

A use-case can be viewed as a “system function”.

Use case assumptions and results can be specified in OCL.

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Components

Specified by an (or more) interface(s)– Operations with pre- and postconditions– Invariants on the objects described by the

interface• Show business rules for the component

OCL 2.0 Message clause– Specify user visible side-effects

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Business Rules

There may be at most as many caps with winner markers on a pallet as there are crates on the pallet:

context Pallet inv:caps->select(winnerMark = true)->size()

<= crates->size()

SIZEOF SELECT c : Cap FROM self.caps WHERE c.winnerMark = true<=SIZEOF self.crates

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Initial values and derivations

-- The caps in a pallet are derived:

context Pallet::cap

derive: crates.bottles.cap->asSet()

context Bottle::contents

init: 0

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Operation body

The body of a query operation can be specified in OCL

context Bottle::totalWeight() : Integer

body: weight + cap.weight

context Crate::totalWeight() : Integer

body: weight + bottles.totalWeight()->sum()

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Guards

open

closed

close [ contents=capacity ]

Bottlecapacity : Integercontents : Integerweight : Integerdiameter : IntegerneckDiameter : Integer

totalWeight() : Integer

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Expressions in a UML model

The target object in an interaction can be specified.

Object flows in activity diagrams

Parameters to messages and signals

… etc. …

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Queries

OCL is a Query Language– Expressive power >= SQL

• David Akehurst, Canterbury University

Boldsoft– Uses OCL exclusively as a query language to

specify the user interface

Queries can be defined on the model level

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Part 3: The MDA Framework

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MDA

MDA is defined around:– Models– Model Transformations

Important model types:– PIM : Platform Independent Model– PSM : Platform Specific Model

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Basic MDA Framework

SourceModel

TargetModel

TransformationTool

CodePIM PSMTransformation

ToolTransformation

Tool

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MDA Framework

SourceModel

TargetModel

Transformationtool

Transformationdefinition

TransformationTool

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MDA

To enable this we need– Modeling languages– Transformation definitions

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MDA Framework

SourceModel

TargetModel

Transformationtool

Language

Iswritten in Is used

by

Language

Iswritten in

Transformationdefinition

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Defining Languages

model

Iswritten in

metamodel

Isdefined by

Language

Iswritten in meta

language

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MDA Framework

SourceModel

TargetModel

Transformationtool

Transformationdefinition

Language Language

Iswritten in Is used

by

Iswritten in

Meta languageIs writtenin

Is writtenin

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Defining Transformations

A transformation definition maps– Element(s) from the source language

to– Element(s) from the target language

based on the respective language definitions

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SourceModel

TargetModel

Transformationtool

Transformationdefinition

Language Language

Iswritten in

Is usedby

Iswritten in

Meta language

Is writtenin

Is writtenin

Transformationdefinition language

Iswritten in

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Complete MDA Framework

Languages are defined by models– These are metamodels, e.g. UML

These models are written in a metamodeling language:– MOF is the OMGs metamodeling language

Transformation Definition Language– MOF RfP for Query/Views/Transformations

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Part 3: OCL in MDA

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OCL in MDA

OCL is essential for MDA in three ways– More precise models– Definition of Modeling Languages– Transformation definitions

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Defining Languages

UML metamodelContext Class inv:

attributes->isUnique(name)

Classname : Integer

Attributename : String

0..*

owner1

attributes

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UML Metamodel Rules

[2] An AssociationClass cannot be defined between itself and something else.self.allConnections->forAll(ar | ar.participant <> self)

[1] An Interface can only contain Operations.self.allFeatures->forAll(f | f.oclIsKindOf(Operation) or f.oclIsKindOf(Reception))

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UML Profile Rules

Rules for e.g. Java profile:

context Class inv:

generalizations->size() <= 1

Other profiles:– EDOC, CORBA, C++, EAI, UML-EJB, SPE, etc.

etc.

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Transformation Definition

Companyname : Integeremployees : Set(Person)

Personname : String

Companyname : Integer

Personname : String

0..* employees

transforms to

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Transformation Definitions

Transformation ManyAssociationToAttribute (UML, UML) {

source ae : UML::AssociationEnd ;

target att : UML::Attribute;

source condition

ae.multiplicity = MultiplicityKind::many;

target condition

att.visibility = VisibilityKind::public and att.type.isTypeOf(Set);

mapping

ae.name <~> att.name;

ae.type <~> att.type.elementType;

}

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References

MDA Explained, Practice and Promise of the Model Driven Architecture– ISBN unknown, to appear Spring 2003, Kleppe, Warmer & Bast

The Object Constraint Language, Precise Modeling with UML– ISBN 0-201-37940-6, 1999, Warmer & Kleppe

The Object Constraint Language, Getting Your Models Ready for MDA– ISBN 0-321-17936-6, to appear May 2003, Warmer & Kleppe

OCL 2.0 Submission– www.klasse.nl/ocl/subm-intro.html

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Questions

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Part 4: Current Status

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OCL 2.0 Submission

Authoring Team

Jos Warmer, Anneke Kleppe Klasse Objecten

Anders Ivner, Jonas Högström Boldsoft

Martin Gogolla, Mark Richters University of Bremen

Heinrich Hussmann,

Steffen Zschaler

Technical university of Dresden

Tony Clark Kings College, London

Simon Johnston Rational

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OCL 2.0 Submission

Submitters and supporters

Klasse Objecten IBM

Boldsoft Telelogic

University of Bremen Project Technology, Inc.

Technical university of Dresden Adaptive Ltd.

Kings College, London Compuware

Rational Software Corporation University of York

IONA University of Kent

Kabira Technologies, Inc.

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OCL 2.0 Submission Highlights

Full UML query language

Complete OCL metamodel full integration with UML metamodel

Concrete syntax strictly separated from abstract syntax allows alternative syntaxes, including visual ones

Semantics defined mathematically and in UML

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UML 2.0 Structure

Infrastructure (ad/00-08-08)

– Simple and extensible UML core

Superstructure (ad/00-08-09)

– Higher level UML structures

OCL (ad/00-08-10)

– General purpose UML expression language

Diagram interchange (ad/00-08-11)

– Exchange visual UML models between tools