Systems Analysis and Design II

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Systems Analysis and Design II

• Behavioral Modeling

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Outline of the course

• Process Model and Software Development Life Cycle
• Software Models and UML 2.0
• Analysis and Requirements
• Requirements elicitation
• Functional Models
• Structural Models
• Dynamic Models
• Design Basics and Software Architectures
• Business, Architecture and Runtime Patterns
• Implementation, Mapping the Design to Code
• Software Testing and Reliability
• Software Performance
• Project Management and Software Economics

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Dynamic Modeling with UML

• Diagrams for dynamic modeling
• Interaction diagrams describe the dynamic
  behavior between objects
• Statecharts describe the dynamic behavior of a
  single object
• Interaction diagrams
• Sequence Diagram
• Dynamic behavior of a set of objects arranged in
  time sequence.
• Good for real-time specifications and complex
  scenarios
• Collaboration Diagram
• Shows the relationship among objects. Does not
  show time
• State Chart Diagram
• A state machine that describes the response of an
  object of a given class to the receipt of outside
  stimuli (Events).
• Activity Diagram A special type of statechart
  diagram, where all states are action states

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Dynamic Modeling

• Definition of dynamic model
• A collection of multiple state chart diagrams,
  one state chart diagram for each class with
  important dynamic behavior.
• Purpose
• Detect and supply methods for the object model
• How do we do this?
• Start with use case or scenario
• Model interaction between objects gt sequence
  diagram
• Model dynamic behavior of a single object gt
  statechart diagram

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Sequence Diagram Syntax
AN ACTOR AN OBJECT A LIFELINE A FOCUS OF
CONTROL A MESSAGE OBJECT DESTRUCTION
anObjectaClass
aMessage()
x
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Sequence diagram
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Arrow label
predecessor sequence-expression return-value
message-name argument-list
move (5, 7)
Sequence numbering schema 1 actionA 1.1.
firstSubactionOfActionA 1.2.
secondSubactionOfActionA 1.3.
thirdSubactionOfActionA 2 actionB 2.1.
firstSubactionOfActionB 2.1.
secondSubactionOfActionB ...
3.7.4 move (5, 7)
3.1 res getLocation (fig)
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Different kinds of arrows
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Example Different Arrows
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Heuristics for Sequence Diagrams

• Layout
• 1st column Should correspond to the actor who
  initiated the use case
• 2nd column Should be a boundary object
• 3rd column Should be the control object that
  manages the rest of the use case
• Creation
• Control objects are created at the initiation of
  a use case
• Boundary objects are created by control objects
• Access
• Entity objects are accessed by control and
  boundary objects,
• Entity objects should never call boundary or
  control objects This makes it easier to share
  entity objects across use cases and makes entity
  objects resilient against technology-induced
  changes in boundary objects.

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Is this a good Sequence Diagram?
Seat
Onboard Computer
Smart Card
Establish Connection

• First column is not the actor
• It is not clear where the boundary object is
• It is not clear where the control object is

Establish Connection
Accept Connection
Accept Connection
Get SeatPosition
500,575,300
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Communication Diagrams

• Essentially an object diagram that shows message
  passing relationships instead of aggregation or
  generalization associations.
• Emphasize the flow of messages among objects,
  rather than timing and ordering of messages

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Example Communication Diagram
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Communication Diagram
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Creating Communication Diagrams

• 1. Set the context.
• 2. Identify which objects (actors) and the
  associations between the objects participate in
  the collaboration.
• 3. Layout the communication diagram.
• 4. Add messages.
• 5. Validate the communication diagram.

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Sequence and Communication Diagram Differences
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Behavioral State Machines

• The behavioral state machine is a dynamic model
  that shows the different states of the object and
  what events cause the object to change from one
  state to another, along with its responses and
  actions.

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Statechart Diagrams

• Graph whose nodes are states and whose directed
  arcs are transitions labeled by event names.
• We distinguish between two types of operations in
  statecharts
• Activity Operation that takes time to complete
• associated with states
• Action Instantaneous operation
• associated with events
• associated with states (reduces drawing
  complexity) Entry, Exit, Internal Action
• A statechart diagram relates events and states
  for one class
• An object model with a set of objects has a
  set of state diagrams

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State

• An abstraction of the attributes of a class
• State is the aggregation of several attributes a
  class
• Basically an equivalence class of all those
  attribute values and links that do no need to be
  distinguished as far as the control structure of
  the system is concerned
• Example State of a bank
• A bank is either solvent or insolvent
• State has duration

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Behavioral State Machine Diagram Syntax
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Example of a StateChart Diagram
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Building Behavioral State Machine Diagrams

• Set the context
• Identify the initial final, and stable states of
  the object
• Determine the order in which the object will pass
  through stable states
• Identify the events, actions, and guard
  conditions associated with the transitions
• Validate the statechart diagram

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Modeling Concurrency

• Process
• Independent address space.
• Execute concurrently with other processes.
• Threads
• Hidden inside a process.
• Not independently scheduled by OS
• Processes and threads run concurrently and
  compete for shared resources

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Object and Threads

• Passive objects depend on external power (thread
  of execution)
• Active objects self-powered (own thread of
  execution)

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Passive Objects Dynamic Semantics

• Encapsulation does not protect the object from
  concurrency conflicts!
• Explicit synchronization is still required

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Synchronization

• Active gt passive object communication lead to
  multiple flows of control in one object at the
  same time.
• State corruption may occur ? need for mutual
  exclusion.
• Use synchronization to implement critical regions

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Synchronization in Activity Diagrams

• Forks and joins implies parallelism and
  synchronization
• Joins waits for all flows to arrive (sync)

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Convenience Features

• Fork transitions can have guards.

• Instead of doing this

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Convenience Features

• Partitions are a grouping mechanism.
• Swimlanes are the notation for partitions
• They may represent an object or set of object
  performing the contained actions.
• They do not provide domain-specific semantics.
• Tools can generate swimlane view from
  domain-specific information without partitions.

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Convenience Features
Signal

• Signal send icon

• translates to a transition with a send action.

• Signal receipt icon

• translates to a wait state (a state with no
  action and a signal trigger event).

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Your Turn

• What distinguishes the sequence diagram, the
  collaboration diagram, and the behavioral state
  machine diagram?
• For what sort of new applications might you need
  to develop all of these? Are there any new
  applications that would not need all of these
  diagrams for full development?

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Summary

• Sequence diagrams illustrate the classes that
  participate in a use case and the messages that
  pass between them.
• Collaboration diagrams provide a dynamic view of
  the object-oriented system and accentuate message
  passing between collaborating actors and objects.
• Behavioral State Machine diagrams show the
  different states that a single class passes
  through in response to events.

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More info

• Each year the Association for Computing Machinery
  (ACM) sponsors a conference on object oriented
  programming. For details about future
  conferences and other ACM programs check
• http//oopsla.acm.org
• http//www.acm.org
• http//www.omg.org