BVUML Behavioral Validation of UML Diagrams

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BVUMLBehavioral Validation of UMLDiagrams

• Boris Litvak
• Shmuel Tyszberowicz
• Amiram Yehudai

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Project Goals

• Checking consistency of dynamic UML diagrams
• Targeted for software designers
• Have no knowledge in formal logic
• Output needs to be easily understood
• Based on UML standard 1.4
• Pre-implementation stage solution

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UML

• Unified Modeling Language
• Sequence diagram
• Object lifelines and inter-object messages
• Usually describes some scenario
• State diagram
• Single object behavior
• States and state transitions
• Checking consistency of dynamic UML diagrams

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Description

• Algorithmic approach
• Key concept the current object state is the
  conjunction of the states in which the control
  resides
• The basic idea
• The incoming and the outgoing messages from an
  object in the sequence diagram are checked
  against the current object state in the state
  diagram

See UML 1.4 standard
FOR MORE INFO...
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Description

• Implementation problems
• Need to define correspondence between diagrams
  (e.g. terminology)
• Complex State diagrams
• Features that originated in activity diagrams are
  the hardest to handle
• We even use simplified diagrams in this
  presentation, for clarity
• However, BVUML output was run on the original

See UML 1.4 standard
FOR MORE INFO...
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Complex state diagrams

• Composite states
• Concurrent composite states
• Guards
• Choice states
• Fork states
• Join states

• Exiting composite states
• History states
• Transient and persistent states
• Completion transitions

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• CC System
• Target update
• example

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Terminology

• Leg
• Depicted as an arrow in either sequence or state
  diagram
• Sequence and state transitions
• In state diagram usually between two persistent
  states
• In sequence diagram usually between two incoming
  messages
• Common transition concept
• Suitable transitions
• State transitions that are equal to sequence
  transitions
• Current object state
• Conjunction of state diagram states which
  contains all the data about the object

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Complex trace example

• Running (1.7.1) TriggerFinishedRequest
  LegsLeg(1.7.2)
• actionSendConfirmation,
• guardAnswerConfirmed,
• Leg(1.7.3)
• actionWriteLog,
  guardWriteLog
• Running top with
• currentStatestop.Stage2.ContactInt
  elligence
• Running top.Stage2.ContactIntelligence
  (externally)
• Running TriggerFinishedRequest Leg
• to top.Stage2.Answered.
• Trying Leg
• actionSendConfirmation,
• guardAnswerConfirmed
• to top.Stage2.WillingToAnswer ...
  success.
• Trying Leg guardNoAnswer
• to top.Stage2.EndIntUpdate ...
  failure.
• Trying Leg guardNoLogWrite
• to top.Stage2.EndIntUpdate ...
  failure.
• Trying Leg actionWriteLog,
  guardWriteLog

• Single transition
• Running (1.7.1) TriggerFinishedRequest
  LegsLeg(1.7.2) actionSendConfirmation,
  guardAnswerConfirmed,
• Leg(1.7.3) actionWriteLog,
• guardWriteLog
• Running top with currentStates
  top.Stage2.ContactIntelligence
• Running top.Stage2.ContactIntelligence
  (externally)
• Running TriggerFinishedRequest Leg
  to top.Stage2.Answered.

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Complex trace example (cont.)

• Trying Leg actionSendConfirmation,
  guardAnswerConfirmed
• to top.Stage2.WillingToAnswer
  ... success.
• Trying Leg guardNoAnswer
• to top.Stage2.EndIntUpdate ...
  failure.
• Trying Leg guardNoLogWrite
• to top.Stage2.EndIntUpdate ...
  failure.
• Trying Leg actionWriteLog,
  guardWriteLog
• to top.Stage2.EndIntUpdate ...
  success.

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Inconsistency An example

• Using a cellular phone scenario
• Dial some digits
• There is an incoming call
• Pressing Send must answer the call

FOR MORE INFO...
Example taken from Robert C. Martins UML tutorial
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Inconsistency Dialer state diag.
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Inconsistency An example (cont.)

• In leg 6 (send button pressed), the sequence
  diagram designer intended to make a call
  (ConnectAction is invoked)
• In the state diagram, when a call is answered at
  the AnswerWait state, AnswerAction is expected

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BVUML run trace

• Running (005) TriggerIncomingCall Legs
• Running top with currentStatestop.Idle
• Running top.Idle (externally)
• Running TriggerIncomingCall Leg
• to top.AnswerWait. ...
  success
• Running TriggerSend Leg
  actionConnectAction
• to top.OnLineWait. ...
  failure
• Running TriggerDigit Leg
• to top.Idle. ... failure

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BVUML run trace (continued)

• Running (006) TriggerSend LegsLeg(007)
• actionConnectAction
• Running top with currentStatestop.AnswerWait
  
• Running top.AnswerWait (externally)
• Running TriggerSend Leg
  actionAnswerAction
• to top.OnLineWait. ...
  failure
• Running TriggerDigit Leg to
  top.AnswerWait. ... failure

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Algorithm (top) view

• For each object in the sequence diagram iterate
  over its sequence transitions
• For each such a sequence transition SeqT, find a
  suitable transition StateT in the state diagram
  of the object
• StateT must emanate from the current object state

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Algorithm (top) view - remarks

• Hierarchical structure
• Composite states include other states and
  redirect algorithm control flow to them
• Transient and persistent states
• Exception completion transition
• BFS traversal while searching for suitable
  transitions from a persistent state

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Algorithm Composite State

• Run step(SequenceTransition) for each child state
  in the current object state
• Possible results
• Ambiguity (non-deterministic)
• None found
• Success

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Algorithm Persistent State

• gatherResults(SequenceTransition)
• Tries to find a suitable transition from (almost)
  each emanating leg
• Completion transition is taken in account
• step(SequenceTransition)
• gatherResults(Transition)

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Algorithm Persistent State Leg

• searchDown(fromState, Legs)
• Tries to find a suitable transition that emanates
  from fromState
• Logic for final, finish, join, and fork states,
  completion transition
• step(SeqTransition, fromState)
• Tries to match the object to the sequence
  transition
• If ok, returns searchDown(targetOfThisLeg,
  remaining sequence diagram legs)

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Design Decisions

• XMI Parser mediator layer
• Parser vendor independence
• Saturateable states
• Composite states, join state
• Fork implementation
• Current object (sub)state is held in the
  composite state that is the parent of the fork
  state
• It is not held in the target composite state

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Design Decisions (cont.)

• Forks and joins as states
• UML1.3 versus UML1.4
• Holding state information
• Single threaded solution
• Concurrent composite states, forks
• Coarse granularity step
• Persistent state receives SequenceTransition as
  an argument, and not a sequence Leg
• Composite states
• Simple composite state is a concurrent composite
  state with one region

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Other approaches

• Code based visual simulations
• Prosasim UML simulator
• Formal logics methods
• HUGO project
• Automatic generation of state diagrams to
  sequence diagrams
• PecSee project
• Theoretic
• Live Sequence Charts (LSC)

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BVUML Summary

• Strengths
• UML input
• Pre-implementation stage
• Algorithmic approach
• Weaknesses
• Covers only the cases shown in the sequence
  diagrams