MOF Meta-Models and UML Profiles

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MOF Meta-Models and UML Profiles

• Jacques Robin

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Outline

• MDAs modeling level hierarchy
• Purposes of meta-models in MDA
• Meta-Object Facility (MOF) a standard language
  for meta-modeling
• Modeling with software abstractions beyond UML
• UML Profiles
• Multi-Agent Simulations
• Others

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MDAs Modeling Level Hierarchy
MOF OCL
Level M3
MOF OCL
Level M2
UML OCL
UML Profile
Special Purpose Modeling Language
AND -OR
AND -OR
Level M1
Running Application
Implementation Running on Platform
Level M0
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Purposes of Meta-Models in MDA

• Define modeling languages
• Their abstract syntax
• Their formal semantics
• Define source and target anchors for model
  transformations
• What about APIs and Libraries?
• They are all written in a given language
• They are thus best viewed as built-in model
  elements to reuse than as part of a modeling
  language
• Thus they should be part of platform models, not
  of language meta-models

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What is Meta-Modeling?

• Meta-Modeling vs. Modeling
• Similar formalisms but different purposes
• One models applications and meta-models
  languages and formalisms
• Meta-Modeling vs. Ontology Engineering
• An ontology is a domain knowledge model, not a
  meta-model
• But a domain is an intermediate level of
  abstraction and generality between application
  and language
• Meta-Modeling Methodologies
• Uncharted territory
• Should integrate and reuse principles and
  techniques from
• Application modeling (formalism similarities)
• Language design (purpose similarities)
• Ontology engineering (process similarities)

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OMGs Meta-Object Facility (MOF)

• Key idea
• Instead of defining entirely new languages for
  the M2 and M3 levels
• Reuse structural core of mature, well-known,
  well-tooled M1 level language (UML
  Infra-Structure)
• Advantages of MOF over traditional formalisms
  such as grammars to define languages
• Abstract instead of concrete syntax (more
  synthetic)
• Visual notation instead of textual notation
  (clarity)
• Graph-based instead of tree-based (abstracts
  from any reader order)
• Entities (classes) can have behavior (grammar
  symbols do not)
• Relations between elements include
  generalization and undirected associations
  instead of only composition and order
• Specification reuse through inheritance
• Additional advantages with OCL
• Allows expressing arbitrary complex constraints
  among language elements (more expressive)
• Allows defining formal semantics without
  mathematical syntax

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MOFMeta-Model Package Structure
UML2 Infra-Structure
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Essential MOF (EMOF) Meta-Model

• Minimum bootstrap elements for modeling,
  meta-modeling and MDA tools
• Includes only classes, attributes, operations,
  packages and primitive types from UML2
  Infra-Structure
• Does not includes associations, which are
  replaces by references (properties whose values
  are classes instead of primitive types)
• Basis for Ecore the metametamodel implemented by
  the Eclipse Modeling Framework
• Any CMOF meta-model can be transformed into an
  EMOF meta-model
• EMOF extends UML2 Infra-Structure with elements
  to represent
• Instances unique identifiers
• Their reflective relations with classes
• Minimal tag-value based extension mechanism

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EMOF Basic Package
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EMOF Basic Package
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EMOF Reflection and Common Packages

• Views any model element as an instance of a
  meta-model meta-class
• Provide operations that cut across MDA layers to
  manipulate model and meta-model elements as
  meta-objects of their meta-classes
• Provides meta-meta-model of a generic reflective
  API to programmatically manipulate models

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EMOF Meta-Model Identifier Package

• OID class property with feature isID true or URI
• Extent OID value range
• useContainment() when true, all contained
  elements are added to containing elements
  extents(recursive containment)
• e.g., if object o1 has property p1 which
  containsobjects o2, which in turns has property
  p2 whichcontains object o3, when
  useContainment() is truethen the extent for o1
  includes o1, o2, o3
• Elements() returns extent members
• URIExtent extent where OIDs are URIsinstead of
  properties
• A URI (Universal Resource Identifier) is either,
• A URL (Universal Resource Locator) providing a
  name for a resource accessible on a network and
  a mean to retrieve it or
• A URN (Universal Resource Name) providing a name
  for a resource in a namespace.

URI syntax and examples URI syntax and examples URI syntax and examples URI syntax and examples URI syntax and examples
scheme authority path query fragment
foo ///example.com8042 /over/there ?nameferret nose
urn exampleanimalferretnose
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EMOF Extension Package

• Any element can be tagged to extend modeling
  language vocabulary

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CMOF Construct Package
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CMOF Reflection
To identify operation parameters by names instead
of merely by position
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Is UML2 Enough? Too Much?

• UML2 covers domain and platform independent
  modeling concepts for the object-oriented,
  relational, imperative, concurrent, event-based,
  distributed and constraint (through OCL)
  computational paradigms
• It does not cover
• Object-oriented reflection
• Functional paradigm which includes powerful
  generative meta-programming and type inference
• Rule-based paradigm which includes powerful
  model transformation mechanisms and general
  logical inference
• Domain-specific modeling concepts
• Platform-specific abstractions
• So it is not enough for key applications and
  domains
• UML2 thus needs an extension mechanism
• But isnt UML2 rather already too much?
• Yes, it is only a vast menu of concepts only a
  few of which are practically useful for a
  particular application or application domain
• To be highly reusable it is also necessarily very
  under-constrained
• So UML2 also needs a reduction mechanism allowing
  a methodology to choose a relevant subset of its
  metamodel and add more stringent OCL constraints
  among the elements of such subset

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Tailored Modeling with Software Abstractions
Beyond UML

• Software abstractions beyond UML can be
  classified as
• Specializing UML abstractions (i.e., UML2
  meta-model elements)
• Generalizing UML abstractions
• Being unrelated to UML abstractions
• Approaches
• No MOF, no UML (the Microsoft way)
• Create and use domain-specific or even
  application-specific meta-modeling, modeling and
  model transformation languages
• Pure MOF, no UML
• Create domain-specific or application-specific
  modeling language that does not reuse any UML
  meta-model element but which is specified as a
  MOF meta-model
• MOF meta-model reuse operators applied to UML
  packages
• Define MOF meta-model of new modeling language
  that reuses UML meta-model elements and add new
  ones
• UML Profile approach (the IBM way)
• Define specializations of UML abstractions by
  stereotyping UML meta-model elements

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Tailored Modeling Domain-Specific Meta-Modeling
and Modeling Approach

• Advantage
• Perhaps easier to integrate with Visual Studio?
• Drawbacks
• For each new domain or application
• Need to redefine entire MDA language
  infra-structure alternative to OMGs
• Need to implement CASE tools for non-standard
  languages

GUI Editor for D2 Diagrams
GUI Editor for D1 Diagrams
D1 Model Repository
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Tailored Modeling Pure MOF Approach

• Pure MOF approach
• Does not use UML
• Advantages
• No need to artificially relate new abstractions
  to UML abstractions
• Drawbacks
• Need to define entirely new meta-model that does
  not reuse any elements consolidated by OMGs long
  meta-modeling experience
• Need to develop entirely new graphical notation
  and editors
• Need to develop all model manipulation services
  (code generation, test generation, reverse
  engineering) that UML CASE tools already provide

UML Editor
GUI Editor for D Diagrams
EMF
generates
Menu Editor for D Diagrams
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Tailored ModelingMeta-Model and MOF Reuse
Operators

• Advantages
• Reuses consolidated elements from UML2
  meta-model
• Drawbacks
• Need to extend UMLs graphical editors to draw
  elements in D\UML2
• Need to extend model manipulation services
  (code generation, test generation, reverse
  engineering) of UML CASE to modeling elements in
  D\UML2
• Current MOF operators do not cover UML2 concept
  generalizing reuse, only reuse as is or as
  specialization

ltlt reuse gtgt
UML Editor
GUI Editor for D Diagrams
EMF
generates
Menu Editor for D Diagrams
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Tailored Modeling UML Profile Approach

• UML2 meta-classes sub-categorized by stereotypes
• Advantages
• Maximum reuse the entire OMG language
  infra-structure
• Maximum reuse of UML CASE tools (no need to
  develop any new tool)
• Drawbacks
• Risk to artificially recast modeling
  abstraction as specializations of UML ones
• Little to reuse for non-object oriented modeling
  languages

Promotes property value to the metaclass level
EMF
meta-class
Package
Class



Profile
Stereotype
ExtensionEnd
Extension
UML Editor

icon

Property
Association
ProfileApplication
Image
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UML2 Profiles

• Define 2 primitives to create models from an EMOF
  metamodel
• new(ltOidgt,ltMetaClassgt)
• set(ltHostOidgt, ltPropertygt,
  ltValueOidgt)
• Example 1
• new(c,Component)
• set(c,Extension,e1)
• set(e1,ExtensionEnd,ee1)
• set(ee1,Stereotype,Agent)
• Example 2
• new(a,Association)
• set(a,Extension,e1)
• set(e1,ExtensionEnd,ee1)
• set(ee1,Stereotype,acquires)

ltltagentgtgt a1Component
ltltagentgtgt a2Component
ltltacquiresgtgt
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UML2 Profiles

• Corresponding MOF instantiation API operations
• new(i1,C1)
• set(i1,Extension,e1)
• set(e1,ExtensionEnd,ee1)
• set(ee1,Stereotype,si1)
• new(i2,C2)
• set(i2,Extension,e2)
• set(e2,ExtensionEnd,ee2)
• set(ee2,Stereotype,si2)

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UML2 Extension via Sub-Metaclasses

• Corresponding MOF instantiation API operations
• new(C1,Class)
• new(C2,Class)
• new(S1,Class)
• new(S2,Class)
• new(g1,Generalization)
• set(g1,general,S1)
• set(g1,specific,C1)
• new(g2,Generalization)
• set(g2,general,S2)
• set(g2,specific,C2)
• new(aS1S2,Association)
• set(aS1S2,ownedEnd,oe)
• set(aS1S2,memberEnd,me)
• set(oe,ownedAttribute,S1)
• set(me,ownedAttribute,S2)

neither direct nor inherited association between C
1 and C2
C1
C2
S2 a sub-metaclass of C2
S1 a sub-metaclass of C1
aS1S2
S1
S2
Allowed association between S1 and S2
i1 S1
i1 S1
i1 and i2 can be linked by an instance of
aS1S2 but no reuse of concrete syntax of C1 and
C2
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UML2 Extension via Sub-MetaClasses and Stereotype
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A UML2 Profile Definition Process

1. Create a special purpose meta-model of an
   application domain, language or platform
2. Identify the top-level meta-classes s1, ..., sn
   of this meta-model (i.e., those with no
   generalizations)
3. Identify in the UML2 meta-model, the concrete
   meta-classesg1, ..., gn that are natural
   semantic generalizations of s1, ..., sn
   (respectively)
4. Extend the UML2 meta-model by defining s1, ...,
   sn as sub-meta-classes of g1, ..., gn
   (respectively)
5. Add OCL constraints on s1, ..., sn that specify
   how they specializeg1, ..., gn (respectively)

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MOF Meta-Model of a Simple Multi-Agent
Simulations Modeling Language (MASML)
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MOF Meta-Model of a Simple Multi-Agent
Simulations Modeling Language (MASML)
KBAgent
1..
Agent
ReasoningComponent
KnowledgeBase
KBSentence
1..
PersistentKB
KBAgent
KBComponent
VolatileKB
0..
1..
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UML2 Profile for MAS

• UML2 Meta-Model

• OCL Constraints
• context Agent invinterfacelet r required and
  (i Sensor or Actuator)in r.oclIsKindOf(i)
• context Agent invsignal let s
  required.ownedReception.signal in
  s.oclIsKindOf(Percept or AgentAction)
• context Sensor invagentabstraction.oclIsKindOf(A
  gent)
• ...

• MASML Meta-Model

MAS
Component isActive true
Environment
Agent
ReasoningComponent
Component
Sensor
Interface
Actuator
Percept
Signal
AgentAction
EnvironmentStateModel
KnowledgeBase
Model
KBSentence
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Available UML Profiles

• By OMG
• Enterprise Application Integration (application
  interoperability through standard metadata)
• Enterprise Distributed Object Computing (EDOC)
• QoS and Fault Tolerance
• Schedulability, Performance and Time
• Testing
• Third parties
• Enterprise Java Beans (by Java Community
  Process)
• Software Services (by IBM, supported by Rational
  Software Architect UML CASE tool)
• Knowledge-Based Systems (University of York)
• Data Modeling (by agiledata.org)
• Framework Architectures (UML-F)
• Requirement Engineering with KAOS
• Formal Methods in B (UML-B)
• Embedded System Design