Using UML, Patterns, and Java Object-Oriented Software Engineering Chapter 2, Modeling with UML: UML...

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Modeling with UML:UML 2 Metamodel

Note to Instructor:

The material in this slide set is not contained in the 3rd edition of the text book. It is planned for the 4th edition.

Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 2

Outline for today• From model instances to meta models• MOF meta model hierarchy• How UML relates to MOF

• Example: Use case diagram meta model• Example: Class diagram meta model

• Different notations for the UML meta model describe the same language

• UML Profiles: Adding new members to the family


From Model Instances to Meta Models

Canonical model-instance-relationship:

aPerson is an instance of the class Person• Thus the class Person is a model for aPerson• And aPerson is a model (an abstraction) of a real

person

PersonaPerson <<instanceOf>>

Can we generalize this idea? What is the model for the class Person?


From Model Instances to Meta ModelsCanonical model-instance-relationship:

• The instance aPerson and the class Person are on different levels of abstraction

• The class Person specifies features that characterize the structure and behavior of Persons

The model for the class Person must characterize the structure and behavior of classes



Person <<instanceOf>> <<metaclass>>Class

From Model Instances to Meta Models• Relationship between model and meta-model:

• The meta class Class is a model for the class Person• Since Person is a model (for the instance aPerson),

Class is a meta model (model for models)



From Model Instances to Meta Models• At first this might be confusing, so:

• Think about the different layers of abstraction:• Instances are concrete• Models are an abstract description of the instances• Meta models are an abstract description of models• Meta-meta models are an abstract description of

meta models….


Meta: Where does the word come from?• The word comes from the Greek μετά

(metá, "after") • An editor in the first century assembled

Aristotles’ work• In the bookshelf, it was the book that came “after

physics” (meta physiká)• Aristotle did not use the term metaphysics,

instead he called these topics "first philosophy”.• A core topic of the metaphysics book is

ontology• Ontology: The philosophical study of nature. The

investigation of what types of things exist in the world and what relations these things have to each other.


Questions in Ontology• What is existence?• Is existence a property?• Which entities, if any, are fundamental?• How do the properties of an object relate to the object itself?• What features are the essential, as opposed to merely accidental,

attributes of a given object?• How many levels of existence or ontological levels are there?• What is a physical object? • Can one give an account of what it means to say that a physical

object exists?• Can one give an account of what it means to say that a non-

physical entity exists?• What constitutes the identity of an object?• When does an object go out of existence, as opposed to merely

changing?

Source: http://en.wikipedia.org/wiki/Ontology


Another Branch from Philosophy: EpistomologyEpistomology

• Analysis of the nature of knowledge and how it relates to truth

• What do people know?• How do we know what we know?• Also deals with the tools for the production of

knowledge• In computer science and project management,

we call it knowledge management• What is knowledge?• How is knowledge acquired?• How is knowledge externalized?• ….


A Taxonomy of Philosophy (UML Class Diagram)

Philosophy

Metaphysics Epistomology Ethics


Meta Models

Why do we need them?• Meta models can be used for instance to formalize UML

notations:• The UML is a Language, meta models are used to

describe the grammar• The UML meta model describes all models one can

create using UML• The meta model allows to talk about semantics.


Meta Models

OK, so meta models are cool, but how do I create a meta model?

To approach this problem, we will look at the history of UML’s meta model first.


The History of UML’s Meta Model

• UML 1.0 had a lot of semantic problems• The OMG tried to deal with these problems by

formalizing the language• Idea: Use meta modeling!

• The OMG realized that all that was needed to describe meta models was to use a subset of UML class diagram elements

• Insight: To describe any meta model, the UML class diagram notation itself can be used!


Meta Object Facility (MOF)• In UML 2, the OMG introduced the Meta Object

Facility to create a common basis for meta modeling• MOF specification: http://www.omg.org/mof/• The specification describes how models can be

• exported from an application• imported into another model• transported across a network• stored and retrieved from a repository• rendered into different formats• used to generate application code

14

http://www.omg.org/mof/


Advantages of MOF Compliant Meta Models• MOF compliant models can easily be compared• MOF compliant models can be exchanged in a

standardized way • XMI (XML Metadata Interchange)

• OMG's XML-based standard format for model transmission and storage

• MOF compliant instances can live in the same metadata repository (data warehousing)


The Meta Object Facility (MOF)We have seen this modeling sequence

instance model meta model…• This sequence could be continued forever• 4 models seem to be enough for most modeling problems

• MOF defines a four-layer meta model hierarchy• Layer M0: Information layer (The Application)• Layer M1: Model layer (The UML model)• Layer M2: Meta model layer (The UML meta model)• Layer M3: Meta-meta model layer (The MOF model)

• MOF and UML are aligned• The UML infrastructure contains all the concepts needed for

the specification of UML and MOF• But MOF is not restricted to UML

• Any meta model which is defined by using MOF is called MOF compliant.


Meta model hierarchy of the MOF (UML-specific)

Layer M0: Run-time Instances• Real instances of the modelsLayer M0 contains concrete run-time instances

• Note that there is a difference between real instance and instance specification!



Layer M1: UML-modelBy using any UML diagram, we instantiate the UML meta model from Layer 2 and obtain a UML model Layer M1 contains application-specific models



Layer M2: UML meta model • Models the language UML, i.e., defines concepts like classes, attributes, associations

Layer M2 contains descriptions of elements that are used to describe the models on the model layer


Meta model Hierarchy of the MOF (UML-specific)



Layer M3: MOF model• The UML meta model is an instance of a yet more abstract model, namely the MOF model

• M3 : M2 ≈ M2 : M1 Layer M3 contains meta-meta models



Remember that UML is only one possibility of modeling with MOF• We looked at a UML-specific hierarchy• MOF describes meta models in general


Where are we?From model instances to meta modelsMOF meta model hierarchyHow UML relates to MOF

• Example: Use case diagram meta model

• Example: Class diagram meta model• Different notations for the UML meta

model describe the same language• UML Profiles: Adding new members to

the family


How UML relates to MOF

• UML is MOF-compliant:The UML meta model is an instance of the MOF model

• Let’s see the UML meta model in action!


Use Case Diagram Meta Model

*

<<instanceOf>>

<<instanceOf>>

<<instanceOf>>

<<Extend>><<instanceOf>>

<<Include>>

<<instanceOf>>

*

*

1

*11 1

* *

1*

*

1..*

0..10..1

UML Meta Model (Layer M2) (Simplified)UML Model for Use Cases (Layer M1)


Class Diagram Meta Model (simplified)

<<instanceOf>><<instanceOf>>

<<instanceOf>>

<<instanceOf>>

0..1

*

0..1 *

0..1

*

0..12..*


Notations for the UML Meta Model

• The UML meta model defines a language for specifying UML models

• The notation used to depict UML models provides graphical icons representing instances of meta model elements

(Sticky figure represents an Actor)• The notation is a mapping from meta model

elements to model elements(“uml-notation(Actor) = “)


UML Profiles

• A lightweight extension mechanism for UML • Concepts partially present in earlier versions

• Stereotypes• Tagged Values

• Established as a specific meta-modeling technique in UML 2.0

• Contains mechanisms that allow meta classes from existing meta models to be extended

• ability to tailor the UML meta model for different platforms or domains

• consistent with the OMG Meta Object Facility (MOF).


UML Profiles

• Consist of stereotypes, tagged values and constraints

• Customize UML models for particular domains or platforms

• Are applied to elements of the UML meta model (M2 Layer)

• Are developed by manufacturers or standardization organizations (CORBA, .NET)

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Applying a Stereotype• The attributes of a stereotype are called tagged

values• Applying a stereotype to an instance of a meta

class means instantiating the stereotype• If the stereotype has attributes, you have to provide

values for them • Confused? See following slide…


Applying a Sterotype (ctd)


Applying UML Profiles

• By applying a UML profile, we • Apply stereotypes to meta classes• Get a deeper understanding for the model• Narrow the amount of valid models.


UML Profiles

All models (MOF)

UML models

CORBA models(profile)

SysML models

.NET models(profile)

U2TP (profile)


SysML (Systems Modeling Language)• SysML is a general-purpose modeling language

for systems engineering applications• Supports the specification, analysis, design, verification

and validation of systems and “systems of systems”. • Proposed in 2001 to improve the specification of

functional and nonfunctional requirements• Use Cases allow the specification of requirements

only on a very high level. • Defined as a UML profile • SysML has two new diagrams (requirements

diagrams and parametric diagrams) in addition to the existing UML diagrams


Requirements Diagram• A SysML requirements diagram is a graphical notation that

describes the requirements of a system in a graphical notation

• Requirements can be linked to other requirements• Requirement elements can also be linked to Use Cases

and Components that realize the requirements (enabling traceability of requirements).


Additional Information• MOF Home Page

• http://www.omg.org/mof/• MOF Specification, Current Version 2.0

• http://www.omg.org/technology/documents/modeling_spec_catalog.htm#MOF

• RSS Feed:• feed://www.omg.org/mof/rss/index.xml

http://www.omg.org/technology/documents/modeling_spec_catalog.htm#MOF

http://www.omg.org/technology/documents/modeling_spec_catalog.htm#MOF

Using UML, Patterns, and Java Object-Oriented Software Engineering Chapter 2, Modeling with UML: UML...

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