Metamodeling and the Model Driven Architecture

(MDA) Paolo Ciancarini

Agenda

  Model Driven Engineering   Metamodeling   Metamodeling in UML   Model Driven Architecture   OMG technologies for MDA

Enterprise Computing   Software is a complex and expensive product   Enterprise Computing adds further requirements:

  Rapid change in organizational assets   Continuous evolving partnerships   Heterogeneous end-user clients

  e.g., Fat clients, Web clients, Cellular Phone, iPod, DTT TV   Need for information ubiquity

  e.g., in mobile/opportunistic networking, cross-network roaming

  The only thing we can predict with confidence about the future of software platforms is that things we cannot predict will happen

Motivations

  There is a strong pressure on the industry to increase   Quality   Longevity   Reusability of software products, while reducing costs

  In order to fulfill this needs the productivity of the software industry must be improved

  Most increments in software productivity are obtained increasing the abstraction level

Levels of abstractions

  The history of software development is a history of raising the level of abstraction

•  In Programming Languages •  e.g., Assembler, C, C++, Visual C#, …

•  In Software Architectures

•  e.g., Client-Server, n-tier, SOA, …

•  In Operative Systems

•  e.g., Virtual Machines, Middleware, Grid

•  In data representation

•  e.g., File, Database, XML, …

A stack of Programming Languages

0s and 1s

3GL

Assembly Language

Model Driven Engineering (MDE)   MDE is a software development method for handling the

complexity of software platforms and related problems   Main feature: “Everything is a model”: the models are first-

class abstractions closer to domains than to algorithmic ideas and concerns

  A model is a simplified representation of a part (i.e. a system) of the real world

Model

System isRepresentedBy

the real world

the modeling space

MDE: Approaches

  MDE concepts can be applied in different ways producing different approaches, each one relying on a specific set of tools

Example: EMF

  The Eclipse Modeling Framework (EMF) is a modeling framework and code generation facility for building applications based on a structured data model

  From a model specification described in XMI, EMF produces a set of Java classes for the model, a set of adapter classes that enable viewing and editing the model, and a basic editor

  Models can be specified using annotated Java, UML, XML documents, or modeling tools, then imported into EMF

  EMF itself provides the foundation for interoperability with other EMF-based tools and applications

Approach Requirement model:

defines the system in its environment

Analysis and design model: defines the

system architecture

Realization model: defines how the system is built

Code of the system and configuration artifacts

Models represent systems   A model is a set of statements about some system

under study   A system S is a delimited part of the world considered

as a set of elements in interaction   A model M is a representation of a given system S

satisfying the principle of substitutability   Principle of substitutability: A model M is said to be a

representation of a system S for a given set of questions Q if, for each question q in Q, the model M will provide exactly the same answer that the system S would have provided in answering the same q

  The relation between a model and a system is called representation of

Models and Reality

A class diagram models a set of objects

Example with three levels

Discuss

  A model which describes a model is called metamodel

  Metamodels are descriptions of descriptions: why are they important to develop software?

Genesi, 2:19

So out of the ground the Lord God formed every beast of the field and every bird of the air, and brought them to the man to see what he would call them; and whatever the man called every living creature, that was its name

Metamodeling

Meta-model A meta-model defines concepts and their relationships thanks to a class diagram

A meta-model only defines structure (no semantics)

A model is an instance of a meta-model if it respects the structure defined by the meta-model

The relation between a model and its metamodel is called conformance

The UML meta-model defines the structure that all UML models must have

+nameUse Case

+nameActor

+nameSystem

1

*

+participate

*

*

+super

0..1

+include*

*

*

+extend

0..*

Client

Add Order

PetStore

Buy

Multiple levels of abstractions

Class Association

Objects

Model

Meta-Model

(M0)

(M1)

(M2)

CustomerOrder item quantity

Customer

id

b:CustomerOrder

Mike:Customer

Id= 12345 c:CustomerOrder Item=batter Quantity=<5 tons>

System-Model-Metamodel Relations

  The extraction of an element from system S to build a model M is guided by a meta-model MM

  MM plays the role of “filter” in the selecting from the system S the elements for building the model M

metamodel MM

terminal model M

system S

conformsTo

repOf Representation of

Exercises

  Describe a metamodel for libraries   Describe a metamodel for cars   Describe a metamodel for TV sets   Describe a metamodel for CRC cards   Describe a metamodel for Petri Nets

Four Layered Architecture Layer Description Example

Meta-metamodel Defines metamodel metaClass, metaAttribute, metaOperation

Metamodel An instance of meta-Metamodel. Defines a model

Class, attribute operation, component

Model Language for describing an information domain. Defines a set of related objects that represent a concept

Employee

User object An instance of the model. An example information domain

:Sally

Metadata architecture

OMG Modeling Infrastructure

25

M3

M2

M1

M0

Meta-Object Facility (MOF)

UML Metamodel

Modeling concepts

User Data

Instance_of

Instance_of

Instance_of

4-Layers Metamodeling   A model, or terminal model, (M1) is a

representation of a real object (in M0) conforming to a metamodel (M2)

  A metamodel (M2) is a representation of a set of modelling elements (in M1) conforming to a meta-metamodel (M3)

  A meta-metamodel (M3) is a set of modeling elements used to define metamodels (M2 ed M3) conforming to itself

N.B. M2, M2 and M3 are all “models”. We could represent them using the same modeling language (e.g., UML)

Example

Meta-metamodel •  A metamodel describes information about models •  A meta-metamodel describes information about

metamodels •  Metamodels defined using the same meta-

metamodel -  can be compared for conformance -  can exchange information -  can be used by the same tools that understand

the meta-metamodel

Meta Object Facility (MOF)

•  Enables meta-metamodeling of UML level metamodels

•  It defines a small set of concepts (such as package, class, method, attribute…) that allow to define and manipulate models of metadata (data about data)

•  All definitions are described using a subset UML notation

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MOF Model

MOF Key Abstract Classes

MOF Key Abstract Classes •  ModelElement base Class of all M3-level Classes;

every ModelElement has a name •  Namespace base Class for all M3-level Classes that

need to act as containers •  GeneralizableElement base Class for all M3-level

Classes that support generalization (i.e. inheritance) •  TypedElement base Class for M3-level Classes such

as Attribute, Parameter, and Constant whose definition requires a type specification

•  Classifier base Class for all M3-level Classes that (notionally) define types; examples of Classifier include Class and DataType

33

Main Concrete Classes •  The key concrete classes (or meta-metaclasses) of MOF:

-  Class -  Association -  Exception (for defining abnormal behaviours) -  Attribute -  Constant -  Constraint

Key associations •  Contains: relates a ModelElement to the Namespace that

contains it

•  Generalizes: relates a GeneralizableElement to its ancestors (superclass and subclass)

•  IsOfType: relates a TypedElement to the Classifier that defines its type -  An object is an instance of a class

•  DependsOn : relates a ModelElement to others that its definition depends on -  E.g. a package depends on another package

36

Component

0..1 0..1 0..1

ownedElement

Comment * Link

1..* 1..* 1..* EnumerationLiteral

ProgrammingLanguageType Enumeration Primitive

* * * * * *

1..*

* Object

Parameter defaultValue kind

Instance Namespace

specialization * parent

* child

GeneralizableElement isRoot isLeaf isAbstract

Package

Model

Subsystem DataType Interface deploymmentLocation * resident

*

AssociationClass

Class Node

owner

{ordered}

participant * specification

* AssociationEnd

isNavigable aggregation multiplicity

connection 2..* 2..* 2..* Association

Method body

Operation isAbstract

0..1

qualifier * Attribute initialValue

{ordered} *

specification * * * * * *

* type Generalization

discriminator

Feature visibility

BehaviouralFeature StructuralFeature multiplicity

Classifier

ModelElement name

Element

Relationship *

*

type

importedElement *

*

UML Meta Model

Metaclasses used in class, package, component and deployment diagrams

A fragment of the UML Meta-Model

GeneralizableElement isRoot : Boolean isLeaf : Boolean isAbstract : Boolean

Class

isActive : Boolean

Classifier

Feature

visibility : {public, private, protected}

*

not self.isAbstract implies self.allOperations->forAll(op | self.allMethods->exists(m | m.specification includes (op)))

Well-formedness constraint (OCL)

Meta-Class

Model Elements •  An element is an atomic

constituent of a model

•  Element is the top metaclass in the metaclass hierarchy

•  A model element is a named entity in a model

•  It is the base for all modeling metaclasses in UML -  All other modeling metaclasses are

either direct or indirect subclasses of ModelElement

ModelElement

name

Element

owner

{ordered}

Method body

Operation isAbstract

Attribute initialValue specification

* * * * * *

Feature visibility

BehaviouralFeature StructuralFeature multiplicity

Classifier

*

Features •  Feature is an abstract class

that declares a behavioral or structural property of -  an instance of a Classifier -  the Classifier itself

•  A behavioral feature refers to a dynamic feature of a model element -  E.g. operation or method

•  A structural feature refers to a static feature of a model element -  E.g. attribute

40

•  A classifier is an element that describes behavioral and structural features -  E.g. class, data type, interface, component

•  Classifier is an abstract class that

-  declares a collection of Features, such as Attributes, Methods… -  has a name, which is unique in the Namespace enclosing the

Classifier

Classifier

Component

Structure 1..* 1..* 1..*

EnumerationLiteral

ProgrammingLanguageType Enumeration Primitive

Subsystem DataType Interface deploymmentLocation * resident

* Class Node

Classifier {ordered}

Feature

visibility * Namespace

Classifier

*

1..*

*

Object

Parameter

defaultValue kind

Instance GeneralizableElement

isRoot isLeaf isAbstract

owner

{ordered}

participant *

specification *

AssociationEnd

isNavigable aggregation multiplicity

* type

Feature

visibility

Classifier

*

type

Namespace

•  A classifier is a generalizable element and defines a namespace

•  It can have -  association ends -  parameters -  instances

AssociationClass

Class

Association

Generalization discriminator

Relationship

Relationship •  A relationship is a connection

among model elements

•  UML defines several relationships such as: -  Association -  Generalization

•  UML defines other types of relationships that are not shown in this diagram, such as: -  Dependency -  Flow

Namespace

0..1 0..1 0..1

ownedElement

Namespace GeneralizableElement

isRoot isLeaf isAbstract

Package

Model Subsystem

Classifier

ModelElement name

* importedElement *

*

•  A namespace is a part of a model that contains a set of other model elements -  E.g. Associations and

Classifiers -  the name of an owned

model element is unique within the namespace

•  Namespace is an abstract

metaclass and it subclasses are -  Classifier -  Package

44

Data Types

1..* 1..* 1..*

EnumerationLiteral

ProgrammingLanguageType Enumeration Primitive

DataType

•  UML data types include -  primitive built-in types (such as integer and string) -  definable enumeration types (such as Boolean whose literals are false

and true); enumerations are a user-defined data types whose instances are literals (specified by the user)

•  Programming languages data types

-  are specified according to the semantics of a particular programming language

-  are not portable among languages (except by agreement among the languages)

-  do not map into other UML classifiers

Mapping of UML Models to Metamodel Elements (Example)

Customer Account accountNumber balance overdraftLimit

CreditCard expiryDate

*1..2

withdraw deposit

Saving Chequing

BankSystem

Generalization discriminator

Relationship

Association

Relationship AssociationEnd

isNavigable aggregation multiplicity Class

Classifier Namespace

Package

Attribute initialValue

StructuralFeature multiplicity

Method

BehaviouralFeature

Use Case Diagrams Metamodel

Mapping Use Cases Model to Metamodel

Generalization discriminator

Relationship

Include

Relationship

Actor

Classifier UseCase

Classifier

Extend

Relationship

Open file by typing name Open file by

browsing

Open file

System Administrator

Browse for file

Ordinary User

Attempt to open file that does not exist

«extend» «include»

State Machines (Main Metamodel)

Mapping State Machines to Metamodel

SimpleState

State

PseudoState

StateVertex

Event

Transition

0..1

*

Enter / run motor forwards

Enter / run motor in reverse

Enter / stop motor

Enter / stop motor

openingCompleted

closingCompleted

pressButton

pressButton

pressButton

Closing Open

Opening Closed

Procedure

State

0..1 +entry

0..1

Extension Mechanisms Metamodel

Example

LinearShape startPoint: Point

1..* edge <<geometry>

LineSegment

Path Line Polygon

RegularPolygon

endPoint: Point {startPoint <> endPoint}

{ordered}

{edge->size=1}

{edge->forAll(e1,e2 | e1.length = e2.length)}

length : int length

{length = edge.length->sum}

{edge->first.startPoint = edge->last.endPoint}

Stereotype

GeneralizableElement

Constraint

Model Driven Architecture (MDA)

  MDA is a theory of software construction based on a set of standards provided by the Object Management Group

  MDA is a kind of MDE, that is domain engineering based on developing models of software systems

  The idea of MDA is to exploit a modeling language (such as UML) as a programming language rather than just as a support for design

  This is not a new approach, it has notable ancestors:   Database schemas, generative programming, CASE

tools, WYSIWYG interfaces

MDA Base Components

  MDA is based on a set of technologies that allow:   Domain specification (domain specific

languages)   Modeling and metamodeling   Model transformations which support the

development of a system independently from:   platforms   platforms evolution   application domains

MDA Dimensions   Horizontal: different domains that are not more or less abstract

than others, like business or technology   E.g., marketing, engineering, sales, etc.   E.g., performance, security, fault tolerance etc.

  Vertical: different level of abstraction of the same domain of a system   From physical data, logical data models, middleware,

applications specifications, component assemblies, business process models, business goals and strategies

  Evolutionary: different systems, legacy, ongoing and upcoming, as-is, as-was and as-could-be   This is technically similar to the horizontal dimension, but it is

more concerned with evolution-focused architectural rules and modeling standards

MDA: the Big Picture

This picture gives some insights about the technologies constituting MDA together with the platforms, the kinds of application and the domains of application that it addresses

Key Idea

  create a source model   independent from platform implementation details   transform it in a target model richer of details than the

source model   Use of a proper transformation language

Basic Concepts

  Model: a simplified representation of   a system   a part of a system   a set of system functionalities

  Point of view: an abstraction technique with the goal of highlighting some features of the system

  View: a representation of the system from the perspective of a particular point of view

Basic Concepts

  Refinement: it is related to a model M1 derived from model M2, where M1 has a number of details greater than M2   M1 is a refinement of M2

  Zooming: when we move from a model with a different level of abstraction than another one   we have like a zoom-effect

  System architecture: the specification of   Components   Connectors   Interaction rules of components by means of

connectors

Basic Concepts

  Model driven: the use of models through all the phases of software development

  Platform independence: a property of a model developed regardless of platform details

  Model transformation: the process of converting one model into another one concerning the same system

Models, metamodels and platforms

MDA: Core Standards

  How do we can specify models, metamodels and meta-metamodels?

  OMG provides a set of standards supporting such activities:   MOF 2.0   UML 2.3   XMI 2.0   CWM 1.1   QVT (Query View Transform)

MOF

  MOF is an OMG standard to write metamodels   Can be used to model the abstract syntax of

Domain Specific Languages   Two flavors: EMOF (Essential MOF), CMOF

(complete MOF)   Kermeta is an extension to MOF allowing

executable actions to be attached to EMOF meta-models, hence making it possible to also model a DSL operational semantics and obtain an interpreter for it

Metamodel   The correspondence between a model and a system is

defined by a metamodel:

  Terminology: a collection of concepts with their properties and relations

  Assertions: a collection of additional rules by which terminology elements can be constrained

Metamodels in Software Engineering

  Currently, metamodels focus on:   Software process modeling (PIF)   Software product modeling (UML, CWM)

  Many new fields are involved:   Model of cost   Model of resource consumption   Models of test, QoS, and software measurements   Requirements modeling (e.g. Use Cases)   Know-how modeling (e.g. Patterns)   Model validation

Meta-metamodel

  A Meta-metamodel provides the language to define a set of metamodels   Definition of abstract syntax: concepts, relationships, and

wellformedness rules   Definition of concrete syntax: shapes, layout, and physical

interchange formats   Definition of semantic domains: the abstract logical space in

which models find their meanings   Definition of mappings between domains

A Metamodel Language: MOF 2.0

  The Meta-Object Facility (MOF) is an OMG specification defining an abstract language and a framework for specifying, constructing, managing, and exchanging, technology-neutral metamodels

  MOF defines a framework for implementing repositories holding the persistent representation of the metamodels

The MOF Meta-metamodel

MOF: Features

  MOF belongs to the MDA architecture   MOF meta-metamodel defined in itself   MOF 2.0 reuses a part of the UML 2.0 metamodel   MOF to XML mapping: OMG XMI (XML Metadata

Interchange) specification   MOF to Java mapping: JMI (Java Metadata

Interchange)

UML 2.0

  UML is a language with a very broad scope covering a large and diverse set of application domains

  It is structured in two main parts:   Infrastructure   Superstructure

  The UML 2.0 metamodel is aligned with the MOF 2.0 meta-metamodel for accomplishing the MDA-vision

  In MDA all the four-layer models are defined by means of UML or its extensions

UML 2.0 Infrastructure

Note: the Core package is the same of the MOF Meta-metamodel

The MDA 4-Layers Architecture (1/2)

  The alignment between UML 2.0 and MOF 2.0 enables to see every UML 2.0 construct like an instance of a MOF 2.0 element   In this way, we can see MOF 2.0 like the meta-

metamodel of UML2   Every UML 2.0 model is an instance of the

UML 2.0 metamodel

The MDA 4-Layers Architecture (2/2)

  The UML metamodel stack is instantiated in MDA by:   M3: MOF 2.0   M2: UML 2.0   M1: An UML 2.0 model at the “class” level   M0: A “real world” object represented by an UML 2.0

model at the “object” level   This stack represents the four-layers architecture

4-Layers MDA: an Example

4-Layers Metamodelling Instance

UML 1.x Metamodel (1/2)

UML 1.x Metamodel (2/2)

UML 2.1 Use-Case MOF Metamodel

XMI

  XML Metadata Interchange (XMI) is the OMG technology for interchanging models in a serialized form

  XMI focuses on the interchange of MOF metadata   i.e., metadata conforming to a MOF-based

metamodel   XMI can also be used for model representation

in model transformations

XMI   XMI uses XML for the transfer syntax and interchange format   XML Document Type Definitions (DTD) or Schema are specified

to enable the transfer and verification of:   UML-based models (e.g. mymodel.xmi, using uml.dtd or

uml.xsd)   MOF-based metamodels (e.g. uml.xmi, using mof.dtd or

mof.xsd)   Models based on other MOF-based meta-models (e.g.

mymodel.xmi using cwm.dtd or cwm.xsd)

CWM   The Common Warehouse Metamodel (CWM)

is the OMG standard for data warehouse   CWM is a specification for modeling metadata

for relational, non-relational, multi-dimensional, and other objects found in a data warehouse

  CWM can be used to extend UML for   supporting data warehouse environments   modeling transformations   structuring transformation specifications

  The goal is to integrate development tools with data deployment solutions

The Metadata Problem CWM addresses the problems facing any company:   Many databases   Many repositories   Different schemas describing the “same” data   Moving data requires manual schema

transformation

CWM Integrates Data

  CWM integrates existing data models

  Maps to existing schemas

  Supports automated schema generation

  Supports automated database loading

  The basis for data mining and OLAP (OnLine Analytical Processing) across an enterprise

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CWM Defines Metamodels

  CWM Foundation

  Relational Data

  Record Data

  Multidimensional Data

  XML Data

  Data Transformations

  OLAP

  Data Mining

  Info Visualization

  Business Nomenclature

  Warehouse Process

  Warehouse Operation

CWM: Fragment of the Relational Metamodel

TableisTemporary : BooleantemporaryScope : String/ trigger : TriggerisSystem : Boolean

ViewisReadOnly : BooleancheckOption : BooleanqueryExpression : QueryExpression

QueryColumnSetquery : QueryExpression

NamedColumnSet/ optionScopeColumn : Column/ type : SQLStructuredType/ usingTrigger : Trigger

SQLSimpleTypecharacterMaximumLength : IntegercharacterOctetLength : IntegernumericPrecision : IntegernumericPrecisionRadix : IntegernumericScale : IntegerdateTimePrecision : Integer

SQLDistinctTypelength : Integerprecision : Integerscale : Integer/ sqlSimpleType : SQLSimpleType

1

*

sqlSimpleType

1

sqlDistinctType *

{ordered}

{ordered}

{ordered}

CheckConstraintdeferrability : DeferrabilityType

*

*

/constrainedElement

*

/constrant*

ColumnSet

SQLDataTypetypeNumber : Integer

Columnprecision : Integerscale : IntegerisNullable : NullableTypelength : IntegercollationName : StringcharacterSetName : String/ optionScopeColumnSet : NamedColumnSet/ referencedTableType : SQLStructuredType

**

/constrainedElement

*

/constraint

*

*

0..1 /feature

*/owner

0..11

*/type

1/structuralFeature*

Pairwise (9 connections)

CWM Tool

Source

Source

Source

Target

Target

Target

Hub (6 connections)

The CWM Metamodel

Extract Transform

Drill Down

Source

Source

Source

Operational Data Sources

Target

Target

Target

Data Warehouses

OMG Metamodel Architecture

Standard Components  Modeling Notation: UML  Metadata Interchange: XMI  Metadata API:

MOF IDL Mapping JMI – MOF/Java Mapping

M I D D L E W A R E

A P P L I C A T I O N

User Data/Object Layer (M0)

Metadata/Model Layer(M1)

Metamodel Layer(M2)

Meta-metamodel Layer (M3)

<Stock name=“IBM” price=“112”/>

Stock: name, price

UML: Class, Attribute CWM: Table, Column ElementType, Attribute

MOF: Class, Attribute, Operation, Association

CWM is based on  UML  MOF  XMI

The CWM Metamodel (1.0) Warehouse

Process Warehouse Operation

Transformation

XML Record Multi- Dimensional Relational

Business Information

Software Deployment

Core

Management

Resource

Analysis

Object (Core+Behavioral+

Relationships)

Foundation

OLAP Data Mining

Information Visualization

Business Nomenclature

Data Types Expressions Keys

Index Type

Mapping

Behavioral Relationships Instance Object Model

Metamodels, Syntaxes and Semantics

  The UML language has been defined by means of a MOF metamodel

  In order to define a MOF metamodel we can use:   MOF to (formally) define the abstract syntax of a set of

modelling constructs   The natural language to (informally) describe some

parts of the semantics   The concrete syntax can be expressed by a

graphical notation or not   Example: a UML diagram can be represented in XML

by means of the XMI concrete syntax   In this case, the XMI file represents the UML diagram

Conclusions

  MDA is a powerful family of technologies   Its basis is metamodeling   The technology of model transformations

(see next lecture) makes the approach practical and powerful

  It is important because it allows to manage automatically the design and maintenance problems typical of large software systems

Self test questions

  What is a model?   What is a metamodel?   What is conformance to a metamodel?   What is MOF?   What is CWM?   Which are the main differences between

UML1.x and UML2.x?

References

  Schmidt, Model-Driven Engineering. IEEE Computer, 39:2(25-31), February 2006.

  Frankel, Model Driven Architecture: Applying MDA to Enterprise Computing, Wiley, 2003

  Mellor, Scott, Uhl, Weise MDA Distilled: Principles of Model-Driven Architecture, Addison-Wesley, 2004

  Mellor & Balcer, Executable UML, a foundation for MDA, Addison-Wesley 2002

  OMG, UML Infrastructure 2.3, 2010

Useful sites

  www.omg.org/mda!  www.ibm.com/developerworks/rational/library/3100.html!

  www.agilemodeling.com/essays/mda.htm!  martinfowler.com/bliki/ModelDrivenArchitecture.html

Interesting tools

  www.eclipse.org/modeling/emf/?project=emf   www.andromda.org   www.bluage.com/   www.openarchitectureware.org   www.openmdx.org   www.ibm.com/developerworks/rational/products/rhapsody/

Questions?