Requirements, Specifications, and Design Using UML

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Requirements, Specifications, and Design Using UML
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Object

• Principal component of an object- oriented
  design
• Includes a set of attributes that define its
  internal state

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An Object is Identified in Two Ways

• By a unique name
• As a member of a class

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Class

• A form of type definition
• all objects derived from the same class have the
  same characteristics, although their attributes
  may have different values
• Defines
• the attributes that an object may have
• the operations that determine how the object
  interacts with the rest of the world

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Class Definition

• Defines both the interface for a particular type
  of object and that objects implementation
• can only read or modify the objects state
  through the operations
• these define the interface to the object

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Interfaces

• Choice of an interface
• proper interface must provide ways to access the
  objects state as well as ways to update the
  state
• need to make the objects interface general
  enough so that we can make full use of its
  capabilities

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Relationships

• Association occurs between classes that
  communicate with each other but have no
  ownership relationship between them
• Aggregation describes a complex class made of
  smaller classes
• Composition a type of aggregation in which the
  owner does not allow access to the component
  classes
• Generalization allows defining one class in
  terms of another

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Derived Classes

• Define one class in terms of another
• e.g. - derive two particular types of displays
• BW_display
• Color-map-display

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Derived Classes

• A derived class inherits all the attributes and
  operations from its base class
• relation is transitive
• if Display were derived from another class, both
  BW-display and Color-map- display would inherit
  all the attributes and operations of Displays
  base class as well

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Inheritance

• One form of generalization
• UML also allows us to define multiple
  inheritance, in which a class is derived from
  more than one base class

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Link

• Describes a relationship between objects
• Association is to link as class is to object

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Behavioral Description
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State Machine

• One method of specifying the behavior of a system

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Events

• Trigger state transitions
• Types
• signal event - an asynchronous
  occurrence
• defined in UML by an object that is labeled as a
  signal
• object in the diagram serves as a declaration of
  the events existence
• because it is an object, a signal may have
  parameters that are passed to the signals
  receiver

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Events - continued

• call event - follows the model of a procedure
  call in a programming language
• time-out event causes the machine to leave a
  state after a certain amount of time
• a time-out is generally implemented with an
  external timer

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Example

• Display Operation

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Sequence Diagram

• Designed to show a particular scenario or choice
  of events
• Display example -- the sequence shows what
  happens when a mouse click is on the menu region

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Home Security Example
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Problem Statement

• This home security system guards against
  break-ins, fire, HVAC failure, and allows
  single-button medical, fire, and police emergency
  calls
• Develop system requirements, specification, and a
  preliminary design

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Requirements/Specifications?
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Wolfs Specification Example Partial
Specification for a Model Train Controller

• Problem Statement capability to smoothly
  control speed and direction of multiple trains
  including an emergency stop control

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Analysis

• User Interface - Control Console
• Controls
• throttle
• emergency stop
• direction
• train selection

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Analysis - continued

• Power Supply constant dc voltage
• Train Motor a dc motor
• speed f(voltage)
• ? pulse width modulation of the dc voltage
• Signaling
• console -- transmitter
• train -- receiver
• ?use modulation on the dc voltage

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Requirements

• Control 1 - 8 trains
• Speed resolution 63 non zero increments in both
  directions
• Controller desire smooth control
• analysis ? need for an inertia constant
• inertia f(mass) f(cars, load, etc)
• need at least 8 different levels
• make a user input

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Requirements - continued

• Emergency stop
• ECC only need error detection

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Requirements Summary Form

• Name Model Train Controller
• Purpose control speed and direction of up to
  eight trains
• Inputs throttle, inertia setting, emergency
  stop, train number
• Outputs train signals

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Requirements Summary Form continued

• Functions set engine direction and speed based
  on inertia setting, respond to emergency stop
• Performance update train speed at least 10
  times per second
• Manufacturing cost lt 50
• Power lt10W
• Physical size and weight size of standard
  keyboard, weigh less than 2 pounds

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Develop Specifications
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First Step

• Basis of operation control panel sends
  messages/commands to train controller
• COMMANDS PARAMETERS
• Set-speed speedinteger
• Set-inertia Inertia positive integer
• E-stop none

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Second Step

• Identify objects
• Console
• Train_rcvr aka Receiver
• Develop sequence diagram

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• Note - both Console and Train_rcvr (receiver)
  run continuously

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Model for Commands

• UML base class and derived classes
• ? a class diagram

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Why a Base Class?

• Common features
• header, ECC, train address, etc.

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Model for Control Console and Train Receiver
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• Note - track is an object but not necessary to
  model unless track failure is a requirement

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Next Step

• Refine console and receiver

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Console Functions

• Read state of front panel
• Format messages
• Transmit messages

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Receiver Functions

• Receive messages
• Interpret messages
• Control motor speed and direction

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• Use CLASS DIAGRAMS to model these functions

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For the Console

• The Panel class
• describes the consoles front panel
• contains the analog knobs and hardware to
  interface to the digital parts of
  the system
• The Formatter class
• includes behaviors that know how to read the
  panel knobs and creates a bit stream for the
  required message

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For the Console - continued

• The Transmitter class
• contains analog electronics to send the message
  along the track
• Knobs
• describes the actual analog knobs, buttons, and
  levers on the control panel
• Sender
• describes the analog electronics that send bits
  along the track

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For the Train/Receiver

• The Receiver class
• knows how to turn the analog signals on the
  track into digital form
• The Controller class
• includes behaviors that interpret the commands
  and figures out how to control the motor

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For the Train/Receiver - continued

• The Motor Interface class
• defines how to generate the analog signals
  required to control the motor
• The Detector
• detects analog signals on the track and converts
  them into digital form
• Pulser
• turns digital commands into the analog signals
  required to control the motor speed

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Next Step

• Refine specification to a complete formal
  specification
• In the text, only a partial refinement is
  presented

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• First, refine analog components
• knobs, pulser, sender, detector

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Knobs

• Four physical devices
• Three knobs
• Train number
• Speed
• Inertial Constant
• One button
• E-stop

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• set-knobs() -- behavior (method, operation) to
  set parameters to current train
• when train number setting is changed
• must reset the other controls to the proper
  values for that train
• so that the previous trains control settings are
  not used to change the current trains settings

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Motor Speed and Direction Control

• Direction f(voltage polarity)
• Speed f(average voltage level)

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• Note - still need to refine
• Panel, Formatter, and Transmitter as
  remaining classes of Console
• Motor Interface, Receiver and Controller as
  classes of Train

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For the Panel

• A behavior for each of the controls
• new-settings() -- uses set-knobs() of knobs
  class to change settings

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For the Motor

• Sign of speed determines direction

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For the Transmitter

• Need behavior for each type of message that can
  be sent

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For the Receiver

• Need
• read-command behavior to read message from
  the tracks
• internal variable to hold current command
• internal variable to indicate if command is a
  new behavior
• to determine command is new
• to determine type and parameters of command

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For the Formatter Class

• Holds current settings for all trains
• Need behaviors
• Sendcommand ? transmitter interface
• Operate ? basic functions of class will
  need further refinement
• Panel active ? indicate when panel
  parameters change

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Formatter Dynamic Behavior

• Use a sequence diagram to illustrate the role of
  the formatter during the panels operation

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Refine Operate Behavior

• Use a state diagram for first specification of
  the operate behavior of the formatter class
• watches the panel for activity
• if the train number changes, it updates the
  panel display
• otherwise it causes the required message to be
  sent

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Refinement of Panel-active Behavior

• Again - use state diagram

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Refinement of Train Controller Class
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For the Operate Behavior

• Use state diagram
• operate behavior is called by the receiver when
  it gets a new command
• operate looks at the contents of the message and
  uses the issue-command behavior to change the
  speed, direction and inertia settings as
  necessary

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• Controllers operate behavior must execute
  several behaviors to determine the nature of the
  message
• once the speed command has been parsed, it must
  send a sequence of commands to the motor to
  smoothly change the trains speed

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Class Update

• Need to specify the basic features of messages
  for compatibility
• First - need to specify the number of bits used
  to determine the message type
• Choose three bits, since that gives us five
  unused message codes

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Class Update - continued

• Second - need to include information about the
  length of the data fields, which is determined
  by the resolution for speeds and inertia set by
  the requirements
• Third - need to specify the error correction
  mechanism choose to use a single-parity bit

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