UML Meta Models II Unification of Static and Dynamic Semantics

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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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KernelPackage
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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.) SynonymVariable.

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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.
• ParameterDirectionKinda 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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TheImmutablesPackage
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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
• Association symbol for associations between roles
  etc.

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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 objects 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