UML Meta Models II- Unification of Static and Dynamic Semantic

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							                 -UML Meta Models II-

Unification of Static and Dynamic Semantics
  A Study in redefining the Semantics of the UML
   using the pUML OO Meta Modeling Approach
          Anneke Kleppe and Jos Warmer
                 Klasse Objecten
               http://www.klasse.nl

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                 Objectives
• The static and
  dynamic viewpoints
  on the system can
  not be separated.
• The meaning of a
  model written in
  UML must be
  expressed to be
  understood by users.
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Same Semantics for Different Views




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     4 Layered Meta Model Again!




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                                                 Kernel
                                                 Package
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  Core.model.concepts Package I
• Model Element:
   – a part of a specification or model in UML
• Container:
   – a Model Element that is able to contain other
     Model Elements.
• Classifier:
   – a Model Element that defines a set of definitions
     (or rules) according to which Values can be
     classified.

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   Core.model.concepts Package II
• Definition:
   – a definition of an aspect of a Value.
         • Synonyms: Rule, Property, Feature.
• Immutable Type :
   – a definition of Values that are immutable.
• Role:
   – a classifier, therefore a set of rules, including an
     instance of this type is mutable, and an instance of
     this type may have references to other instances

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 Core.model.concepts Package III
• Name:
     – a reference. (Needs to be instantiated in order to
       pick one UML variant.Usually it takes the form
       of a string type.) Synonym:Variable.




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                Well-Formedness Rules
• Uniqueness of names
• No circular inheritance
• A generalizable element must confirm to its
  paprents




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Definitions in core.instance Package
• Domain Element :
  – an element that can be reasoned about (specified,
    modeled) using the UML.
• Local Snap shot:
  – a collection of Name Value Bindings for a certain
    Mutable Value at a certain point in time.
• Name Value Binding:
  – a combination of a Name (reference) and a Value

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        Definitions of core.instance II
• Value:
  – a Domain Element that represent some of the
    elements of the world that can be modeled in UML
• Mutable Value:
  – a Value that has slots of which the value may
    change.
• Immutable Value:
  – a Value that cannot change, or be changed.

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    Definitions of core.instance III
• Null Value:
     – a Value that represents void (null, nil).
• Object:
     – a Mutable Value that has a state, represented in
       a Local Snapshot, and is able to change that
       state thereby creating a new Local Snapshot.



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                    Well Formedness Rules
• A name value binding contains name and value
• A mutable value contains its snapshots
• History of an object is ordered.
• Slot values of a local snapshot of a mutable
  value may not contain the local snapshot self
• Additional Operations
      – allPredecessors( ):
            • The collection of all previous snapshots

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                                                 Core
                                                 Semantics
                                                 Package




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                Core.semantics Package
• Class: a mutable value that represents a role
• confirmsTo(): is as in pUML metamodel.




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                  The Features Package
• StructFeatureDef: a definition of a feature that will
  not execute and/or change state.
• DynFeatureDef: a definition of a feature that may
  execute and may change state.
• InvariantDef: a definition of a rule, mostly based on
  structural features.
• ParamDef: a definition with a Parameter Direction
  Kind, that can be actualized by an actual parameter.
• ParameterDirectionKind:a definition of an
  enumeration that denotes if the parameter is used for
  supplying an argument and/or for returning a value.
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                                                    The
                                                 Immutables
                                                  Package




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             Definitions in Immutables
• CollectionType:
  – a type that defines values that can hold other
    values.
• DataType:
  – a classifier, therefore a set of rules, including, an
    instance of this type is immutable, and an instance
    of this type has no references to other instances
• EnumerationType:
  – a type that defines a limited set of values.
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                immutables.semantics




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          The Associations Package




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                Why only Unary ?




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  Why Only Unary ? - Explanation
• A one way association to be a restriction of a
  two way association – where one is the inverse
  of the other.
• Consider the previous diagram. The definition
  is recursive. Hence defining inverse is difficult




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            The Associations Package
• Unary Association:
  – a structural feature that can be used to reference
    another mutable value
  – Hence, type can only be a role, or a collection type
• Multiplicity Kind:
  – An indication of the number of elements in the
    collection of the unary association.



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        Well-formedness Conditions
• When the multiplicity is zero or one:
  – the type of a unary association is equal to its
    associated classifier.
• When the multiplicity is zero to many, or one
  to many,
  – The type of a unary association is equal to the pre-
    defined type set, and this set has as element type
    the role of the unary association.


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                  The Action Package - I
• Action Expression:
  – a model element with indicating a value, or an
    action.
• Feature Ref:
  – a reference or a call to a definition
• Primitive Action:
  – an action that specifies a change of the snapshot of
    the mutable value that executes the action


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                 The Action Package - II
• Data Value Exp:
   – an expression of data values and operations.
• Create Object Action:
   – an expression specifying a change of the snapshot of
     a class so that the slot ’new’ contains a new object-
     an instance of that class.
• Read Action:
   – an expression that specifies a certain value.
• Write Action:
   – an action that specifies a change of the value.
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         Compound Actions Package
• Idea: Add
   – Loops, Conditional actions, Group actions
• All sub-actions of a compound action are
  executed by the same object.
• Form the Paper:
   – “Making UML Activity Diagrams Object-
     Oriented” –Tools Europe 2000



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                 The Messaging Package
• Every object is extended with an input and
  an output queue,
  – both of which may contain signals.
• Two new subclasses of Primitive Action
  – SendAction
        • puts a signal in the output queuea
  – ProcessSignalAction.
        • takes a signal out of the input queue.


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message.instance.concepts Package
• Bus:
     – a transport mechanism that transports signals
       from output queue to input queues.
• Signal Instance:
     – an occurrence of a signal.
• SendSignalExec:
     – Execution of the sending of a signal, i.e. putting a
       signal with its content in the out-put queue
• ProcessSignalExec:
     – Execution of the receipt of a signal, i.e. taking a
       signal with its content from the input queue

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message.signal.semantics Package




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      Self Description and OCL
       -some known problems-
• Predefined OCL operations
  (oclIsTypeOf, includes, etc.) are not
  defined in this meta model, but will be
  fixed in OCL 2.0
• Some symbols are overloaded, such as:
     – roles use the class symbol
     – Inheritance symbol for parent-child
         relationship
     – 823            symbol for associations
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                 State Machines
• For statechart diagrams
• This view point is not compatible with the
  thinking
  – the object has a state machine, OR
  – the object’s state machine does …
• Two options:
  – Either the state machine is an attribute of the
    primary object.
  – it is equal to the primary object: This option is
      taken
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                State Machines




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                  Well Formedness Rules
• The test of a Transition is an AND
  combination of its guard, and its from-State.
• The result-type of the state must be of
  Boolean type.
• Only roles may have states.
• The to and from states of a transition must
  belong to the same class as the transition.

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    State Machine Instance Package




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   State Machine Instance Package
• The test of a Transition-Exec checks
  whether the signal-Instance is in the input
  queue of its self object.
• The sub-action of a Transition-Exec is a
  Conditional-Action-Exec.
• A Transition-Exec may only be executed
  by a mutable value that has a role that has
  states for which transitions are defined.
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                More on Statecharts
• The stateMachine package could have
  been defined without introducing the
  concepts State and Transition.
• How?
     – rewriting of the well-formedness rules to
       apply to the parent concepts
     – Invariant-Def AND
     – Conditional-Action.
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       Sequence and Collaboration
               Diagrams
• Interaction diagrams show messaging,
  form the two syntaxes for the
  messaging package.
• Both of the interaction diagrams show
  items on the instance level.
• Only a collaboration diagram may also
  be used as a model diagram, when it is
  used for role modeling.
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Sequence and Collaboration Diagrams
 • Need to establish a relation between:
   – messaging package AND
   – Graph-Symbols package on two levels:
 • Why two levels?
   – Once, for the role modeling of collaboration
     diagram,
         • To the model sub-package of messaging
   – At the level of the Instance Sub-package for
         • Sequence diagrams
         • Collaboration diagrams
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