A Language for Model Transformations in the MOF Architecture Ivan Kurtev, Klaas van den Berg

Sheet 1MDAFA2004 Linköping, June 2004

A Language for

Model Transformations in

the MOF Architecture

Ivan Kurtev, Klaas van den Berg

University of Twente, the Netherlands


Outline

Transformation scenarios; Limitations in current transformation

languages; Uniform representation of model elements

in MOF; Operations in model transformations; Instantiation and Generalization

mechanisms; Conclusions;


Transformation Scenarios

QVT Scenario Transformation specified

between meta models; The context of

Query/Views/Transformation RFP by OMG;

MOF

UMLMetamodel

JavaMetamodel

a UMLmodel

Javaclasses

User dataJava

objects

TransformationDefiniton

TransformationExecution

MOF

DTD MetaModel

RelationalMeta Model

a DTDa Relational

Schema

an XMLDocument

a RelationalDatabaseM0

M1

M2

M3


TransformationExecutionM0

M1

M2

M3

Data Transformation Scenario

Transformation is executed over concrete data instances at level M0;

E.g. Common Warehousing Metamodel (CWM);


Transformation Scenarios

MOF

DTD MetaModel

Java MetaModel

a DTDJava

Classes

an XMLDocument

JavaObjectsM0

M1

M2

M3

SchemaCompilation

Unmarshaling


MOF

DTD MetaModel

UML MetaModel

UML DTDan UMLModel

an XMLDocument

a ModelInstanceM0

M1

M2

M3XMI

Java MetaModel

JavaClasses

JavaObjects

JMI

Data Binding in context of MOF

Transformation specified at level M2 is executed twice in lower levels M1 and M0;

Inter-level Transformations XML Metadata Interchange

(XMI); Java Metadata Interchange

(JMI);


Transformation Techniques QVT Scenario:

5 submissions to OMG, standardization is expected; Data transformation Scenario:

CWM OMG document; Supports object-oriented, relational, XML, record-based

data sources; Data Binding:

proprietary tools, outside the context of MOF architecture; XMI, JMI:

transformations specified with grammars and templates;

There is no single language that addresses all the scenarios.

QVT and CWM languages have similarities but cannot be applied in a different context.


Transformation Techniques

QVT Languages: Execute transformations among models at level M1; Rely on the MOF instantiation mechanism:

Non-abstract Classifiers at level M2 can be instantiated; Attributes become slots; Associations become links;

Disadvantages: QVT languages are not applicable at level M0; Coupled with the MOF instantiation;



Common Warehouse Metamodel (CWM): Reuses the concepts of classes and instances from

UML; Concrete data models (XML, Relational,…) specialize

these concepts; To apply CWM transformations we extend CWM meta

model;

Disadvantages: Can not handle models at level M2 if they do not

specialize CWM;



Summary

Current transformation languages are coupled with particular instantiation and generalization mechanisms

This coupling prevents the existence of a single transformation language for all scenarios

Problem

How to decouple the transformation language from instantiation and generalization mechanisms for a given model?


Approach

Two basic ideas: Represent model elements at

any level of MOF in a uniform way;

Study the impact of instantiation and generalization over a transformation language;

Transformation Language: Operates on the generic

representation; Specifies different

instantiation mechanisms as transformations;

MOF

a Meta-model

a Model

Instances

MOFR

a Meta-modelR

a ModelR

InstancesR

GenericModel

MOFArchitecture

GenericRepresentation

instanceOf

instanceOf

instanceOf


Structure of Model Elements

MOF architecture is a space of model elements; Elements have identity and named slots; This structure is applicable to model elements at any level of

the MOF architecture;

ModelElement

+name

Slot

+value

Literal

1

+slots

1..*

*+value0..*

+slot


Example: MOF Model Representation

Simplified MOF Model

Primitive data types and multiplicity are skipped


MOF Model represented as a set of model elements

Example: MOF Model Representation

Class

ModelElement

Attribute

ModElNameAttr

"Class"

"Attribute"

"name"name

supertype

attributes

GeneralizableElement

Classifier

"ModelElement"

name

"GeneralizableElement"

name

"Classifier"name

name

name

supertype

supertype

supertype

"true"

isAbstract

instanceOfMOF

instanceOfMOF

instanceOfMOF

instanceOfMOF

instanceOfMOF

instanceOfMOF


Multiple InstanceOf Relations

JavaClass

MOF ClassM3

instanceOfMOF

type

JavaObject

a Class an Object

instanceOfMOF

instanceOfMOF instanceOfMOF

instanceOfJavaJavaClass

MOF Class

instanceOfMOF

a Class

an Object

instanceOfMOF

instanceOfJava

M2

M1

M0

InstanceOfMOF – linguistic (physical) instantiation;

InstanceOfJava – ontological (logical) instantiation;


Example: Relational Model

Metamodel of relational schemas and its instances


Two ways to refer to the field A: Navigating over the graph: aTuple.field[name=“A”].value By using the type aSchema: aTuple.A

The first is linguistic, based on InstanceOfMOF;

The second is ontological, based on InstanceOfREL;

Example: Relational Model

aSchema

ft1

"A"

name

fieldTypes

"mySchema"

nameft2"B"

name

Int

type

Boolean

type

aTuple

f1

"A"

name

field

"true"

value

f2 "B"name

'123'

value

instanceOf

RelationalSchemaFieldType

instanceOfMOF

instanceOfMOF instanceOfMOF

Tuple Field

instanceOfMOFinstanceOfMOF

instanceOfMOF

instanceOf

instanceOf


Transformation Language

Models are sets of model elements; Transformations operate on the generic representation

of models; Two types of transformation rules:

Model element rule: creates model elements in the target model;

Slot rules: assign values to slots;

Four basic operations: Selection of source model elements on the base of their type; Instantiating model elements on the base of a type; Accessing slot values; Assigning values to slots;


Modeling Instantiation and Generalization The four operations are affected by instantiation and

generalization mechanisms; Operations rely on a set of primitive functions that implement

various aspects of instantiation and generalization;

Selection Instantiation Slot Access Slot Assignment

meta

getSpecializedConstructs

instantiategetSlotValue

setValue

isCompatible

Instantiation Generalization

transformationoperations

functions

languageconcepts


Modeling Instantiation

Selection: meta(me: ModelElement): ModelElementReturns the meta-construct of a model element

Instantiation: instantiate(meta-construct: ModelElement) : ModelElementCreates an instance of a meta-construct

Slot Access: getSlotValue(me: ModelElement, slotName: String) : Set of ModelElement

Slot Assignment: setValue(me: ModelElement,

slotName: String, slotValue: Set of ModelElement)


Modeling Generalization

Selection: getSpecializedConstructs(me: ModelElement) : Set of

ModelElementUsed for selection on the base of sub-types;

Instantiation: instantiate(meta-construct: ModelElement) : ModelElement Contains knowledge about inheritance

Slot assignment: isCompatible(expectedType: ModelElement, actualtype: ModelElement): Boolean Used to perform type checking


Specifying Transformations

The 6 functions have different implementations for different modeling languages;

Before executing a transformation, the transformation engine is configured with function implementations:

Meta model andConfiguration

Meta model andConfiguration

SourceModel

TargetModel

TransformationEngine

TransformationSpecification

instanceOf instanceOf

based onbased on

input output

executed byinput input


Example: Instantiating Model Elements

Instantiation is treated as a transformation from a model element (the type) to another model element (instance) with empty slots;

Instantiation is defined in the transformation language;

Example: MOF InstantiationMOFClassInstantiation ModelElementRule source [c:Class, condition {c.isAbstract=false}] target [ModelElement {slots}] SlotRules { attributeSlots source [a:Attribute=c.attributes] target [slots] associationSlots source [assoc:Association,

condition {assoc.from.type=c}] target [slots] }

MOFAttributeToSlot ModelElementRule source [a:Attribute] target [Slot {name=a.name}]

MOFAssociationToSlot ModelElementRule source [assoc:Association] target [Slot {name=assoc.to.name}]


Relational schema instantiation:

RelSchemaInstantiation ModelElementRule source [s:RelationalSchema] target [Tuple{field, instanceOfRel =s}]

SlotRules{ Fields source [f:FieldType=s.fieldTypes] target [field]}

FieldTypeToField ModelElementRule source [ft:FieldType] target [Field{name=ft.name}]

Instantiation of Tuple and Field is according to the MOF instantiation

Example: Instantiating Model Elements


Conclusions

The approach enhances the scope of transformations beyond the QVT scenario;

Requires explicit definition of part of a modeling language semantics concerning instantiation and generalization;

Future work: automatically derive transformations over more than one level (the Data Binding Scenario);

Documents

A Language for Model Transformations in the MOF Architecture Ivan Kurtev, Klaas van den Berg