Chapter 2, Modeling with UML: UML 2 Metamodel

1
Chapter 2,Modeling with UMLUML 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.
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

3
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

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

4
From Model Instances to Meta Models

• Canonical 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

5
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)

6
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.

7
Meta Where does the word come from?

• The word comes from the Greek µet? (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.

8
Questions in Ontology
Source http//en.wikipedia.org/wiki/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?

9
Another Branch from Philosophy Epistomology

• Epistomology
• 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?
• .

10
A Taxonomy of Philosophy (UML Class Diagram)
Philosophy
Metaphysics
Epistomology
Ethics
11
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.

12
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 UMLs meta model first.

13
The History of UMLs 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!

14
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

15
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)

16
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.

17
Meta model hierarchy of the MOF (UML-specific)

• Layer M0 Run-time Instances
• Real instances of the models
• Layer M0 contains concrete run-time instances
• Note that there is a difference between real
  instance and instance specification!

18
Meta model hierarchy of the MOF (UML-specific)
Layer M1 UML-model By using any UML diagram, we
instantiate the UML meta model from Layer 2 and
obtain a UML model ? Layer M1 contains
application-specific models
19
Meta model hierarchy of the MOF (UML-specific)

• 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

20
Meta model Hierarchy of the MOF (UML-specific)
21
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

22
Meta model hierarchy of the MOF (UML-specific)

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

23
Where are we?

• 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

24
How UML relates to MOF

• UML is MOF-compliant
• The UML meta model is an instance of the MOF
  model
• Lets see the UML meta model in action!

25
Use Case Diagram Meta Model
UML Model for Use Cases (Layer M1)
UML Meta Model (Layer M2) (Simplified)


1
1

1..
1
1
1





0..1
0..1
26
Class Diagram Meta Model (simplified)

0..1
0..1
0..1
2..

0..1

27
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) )

28
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).

29
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)

30
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

31
Applying a Sterotype (ctd)
32
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.

33
UML Profiles
All models (MOF)
UML models
CORBA models (profile)
.NET models (profile)
U2TP (profile)
34
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

35
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).

36
Additional Information

• MOF Home Page
• http//www.omg.org/mof/
• MOF Specification, Current Version 2.0
• http//www.omg.org/technology/documents/modeling_s
  pec_catalog.htmMOF
• RSS Feed
• feed//www.omg.org/mof/rss/index.xml