The role of OCL in the Model Driven Architecture Jos Warmer Klasse Objecten

Klasse Objecten Part 1 The role of modeling in software development.

Klasse Objecten 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

Klasse Objecten MML 0: No Specification Specification of software is kept in the heads of the developers.  My software …

Klasse Objecten MML 1: Textual Specification of software is written down in one or more natural language documents.

Klasse Objecten 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. +

Klasse Objecten 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. +

Klasse Objecten 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.

Klasse Objecten 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 (  ).

Klasse Objecten 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: ???

Klasse Objecten 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

Klasse Objecten 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.

Klasse Objecten MDA Example  SQL - EJB  EJB - JSP  Platform Independent Model PSM JSPPSM SQLPSM EJB

Klasse Objecten 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).

Klasse Objecten Part 2: OCL

Klasse Objecten Object Constraint Language OCL is about objects OCL is a language OCL is not just about constraints OCL is the UML expression / query language

Klasse Objecten 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

Klasse Objecten 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 (?)

Klasse Objecten Example Model Bottle capacity : Integer contents : Integer weight : Integer diameter : Integer neckDiameter : Integer totalWeight() : Integer Cap innerDiameter : Integer weight : Integer 0..1 cap 0..* bottles Crate capacity : Integer maxWeight : Integer maxDiameter : Integer totalWeight() : Integer addBottle(b : Bottle) 0..1 bottle 0..1 Pallet capacity : Integer maxWeight : Integer totalWeight() : Integer addCrate(c : Crate) 0..1 crates 0..* pallet crate 0..* / caps

Klasse Objecten Invariants on Classes context Crate -- the number of bottles may not exceed its capacity inv: bottles->size() <= capacity -- each bottle must fit in the crate inv: bottles->forAll(diameter < maxDiameter) -- the total weight must be less than the maximum inv: totalWeight() <= maxWeight

Klasse Objecten Invariants on Classes context Crate -- each bottle must fit in the crate inv: bottles->forAll(diameter < maxDiameter) FORALL b : Bottle FROM bottles ISTRUE b.diameter < maxDiameter

Klasse Objecten State invariants context Bottle state Closed inv: contents = capacity open closed Bottle capacity : Integer contents : Integer weight : Integer diameter : Integer neckDiameter : Integer totalWeight() : Integer

Klasse Objecten Design by Contract Pre- and post-conditions Takes “Design by Contract” principle into “Analysis by Contract”

Klasse Objecten 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 bottles post: bottles =

Klasse Objecten Use Case Pre/Postcondtions A use-case can be viewed as a “system function”. Use case assumptions and results can be specified in OCL.

Klasse Objecten 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

Klasse Objecten 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() size() SIZEOF SELECT c : Cap FROM self.caps WHERE c.winnerMark = true <= SIZEOF self.crates

Klasse Objecten Initial values and derivations -- The caps in a pallet are derived: context Pallet::cap derive: crates.bottles.cap->asSet() context Bottle::contents init: 0

Klasse Objecten 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()

Klasse Objecten Guards open closed close [ contents=capacity ] Bottle capacity : Integer contents : Integer weight : Integer diameter : Integer neckDiameter : Integer totalWeight() : Integer

Klasse Objecten 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. …

Klasse Objecten 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

Klasse Objecten Part 3: The MDA Framework

Klasse Objecten MDA MDA is defined around: –Models –Model Transformations Important model types: –PIM : Platform Independent Model –PSM : Platform Specific Model

Klasse Objecten Basic MDA Framework Source Model Target Model Transformation Tool CodePIMPSM Transformation Tool Transformation Tool

Klasse Objecten MDA Framework Source Model Target Model Transformation tool Transformation definition Transformation Tool

Klasse Objecten MDA To enable this we need –Modeling languages –Transformation definitions

Klasse Objecten MDA Framework Source Model Target Model Transformation tool Language Is written in Is used by Language Is written in Transformation definition

Klasse Objecten Defining Languages model Is written in metamodel Is defined by Language Is written in meta language

Klasse Objecten MDA Framework Source Model Target Model Transformation tool Transformation definition Language Is written in Is used by Is written in Meta language Is written in Is written in

Klasse Objecten 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

Klasse Objecten Source Model Target Model Transformation tool Transformation definition Language Is written in Is used by Is written in Meta language Is written in Is written in Transformation definition language Is written in

Klasse Objecten 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

Klasse Objecten Part 3: OCL in MDA

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

Klasse Objecten Defining Languages UML metamodel Context Class inv: attributes->isUnique(name) Class name : Integer Attribute name : String 0..* owner 1 attributes

Klasse Objecten 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))

Klasse Objecten 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.

Klasse Objecten Transformation Definition Company name : Integer employees : Set(Person) Person name : String Company name : Integer Person name : String 0..* employees transforms to

Klasse Objecten 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; }

Klasse Objecten 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 , 1999, Warmer & Kleppe The Object Constraint Language, Getting Your Models Ready for MDA –ISBN , to appear May 2003, Warmer & Kleppe OCL 2.0 Submission –

Klasse Objecten Questions

Klasse Objecten Part 4: Current Status

Klasse Objecten OCL 2.0 Submission Authoring Team Jos Warmer, Anneke KleppeKlasse Objecten Anders Ivner, Jonas HögströmBoldsoft Martin Gogolla, Mark RichtersUniversity of Bremen Heinrich Hussmann, Steffen Zschaler Technical university of Dresden Tony ClarkKings College, London Simon JohnstonRational

Klasse Objecten OCL 2.0 Submission Submitters and supporters Klasse ObjectenIBM BoldsoftTelelogic University of BremenProject Technology, Inc. Technical university of DresdenAdaptive Ltd. Kings College, LondonCompuware Rational Software CorporationUniversity of York IONAUniversity of Kent Kabira Technologies, Inc.

Klasse Objecten 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

Klasse Objecten UML 2.0 Structure Infrastructure (ad/ ) –Simple and extensible UML core Superstructure (ad/ ) –Higher level UML structures OCL (ad/ ) –General purpose UML expression language Diagram interchange (ad/ ) –Exchange visual UML models between tools