Analysis of Requirements

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Analysis of Requirements

• Developed by Gretel Coombs
• VESL Project - NSF Grant
• under the direction of Dr. Betty Cheng

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Analysis

• Steps to follow
• Obtain Problem Statement or Initial
  Requirements
• Build an object model and Data Dictionary
• Develop a dynamic model
• Construct a functional model
• Verify, iterate, and refine the three
  models
• Produce Analysis Document

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OMT Analysis and Modeling of Embedded Systems
OMT models
object model
dynamic model
Problem?
functional model
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Benefits of 3 models

• A developer can take a problem and begin to
  understand the requirements through the creation
  of these three models of OMT.
• The 3 views helps reduce the inherent complexity
  of the system by only capturing some of the
  information on each graph.
• The notation on each graph is relatively easy to
  understand and learn.

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Object Model Review

• The object model shows the static structural
  aspects of a system.
• The notation includes
• Rectangle Class
• Class are real world objects that are grouped
  together.
• Class name on top and optional attributes and
  operations.
• Line Associations
• between objects
• unannotated means one-to-one association.

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More Object model notation

• DiamondAggregation of
• several objects aggregated into one composite
  objects.
• Ex most embedded system is a composite object
  made up of 4 aggregate classes.
• Triangle inheritance.
• Attributes and operations of the superclass are
  inherited by the subclasses.
• For example the specific sensor objects all
  inherit some similarities from the sensor
  superclass.

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Object Model Four main system objects or classes

• Controller object
• might be made up of several controllers
• is the brains of the system.
• Takes input from the sensors and gives
  instructions to the actuators.
• Sensor object
• environmental objects that gives information to
  controller.
• Can be passive (thermometer) or active (button).

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Object Model Four main system objects (continued)

• Actuator object
• Environmental objects that are controlled by the
  controller.
• Can be turned on or influenced by controller.
• Examples User indicator lights, motors, burners.
• User Interface object
• A display for the user.
• Can be made up of both sensors and actuators.
• Example machine control panel

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Step One Develop a high-level object model
Embedded System
Controller
Actuator
User-Interface
Sensor
Button
Pedal
Inheritance
Class Name
Class
Zero or more
Attribute()
Association
Aggregation
Operation()
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Review of Dynamic Model

• A dynamic model is a type of state machine.
• System can only be in one state at a time.
• Arrows Transitions
• from one state to another happen
• when events happen.
• Events are labeled on the transitions.
• Guards are conditions that keep a transition from
  happen, such as is in neutral or park

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Step Two Develop a system-level dynamic model
On button pushed in neutral or park
Idle or off state
Running state
Off button pushed
State
Transition
condition Guard
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Functional Model

• Dataflow diagram showing
• flow of data in system
• processes that do data transformations.
• In embedded systems dataflows are often control
  information.
• Notation
• Ovals processes
• Arrows dataflows
• Rectangles actors

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Step Three Develop a system-level functional
model
System Process
input
output
Sensors
Actuators
process
actor
dataflow
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Example Automotive Door Control

• The system controls the windows and door locking
  functions.
• All doors have window roll up and down controls.
• Drivers door has window lock feature.
• Driver and front passenger have door lock and
  unlock toggle.
• Fob unit for locking and unlocking doors, with
  driver notification (horn honk and lights flash.)
• Three concurrent systems identified.

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Summary of development process

• The object model shows the real world objects
  grouped in classes with attributes and operations
  and associations.
• The dynamic model shows the control aspects with
  superstates refined into substates.
• The functional model shows signals and data
  flowing through system, with the processes
  refined according to the controller objects.

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References and Readings

• Coombs, G. Object-Oriented Design of Embedded
  Systems with Translation to VHDL. Masters
  Thesis, Michigan State University,1998.
• Rumbaugh, J., Blaha, M., Premerlani, W., Eddy,
  F., and Lorensen, W. Object-Oriented Modeling
  and Design. Prentice Hall, Englewood Cliffs, New
  Jersey, 1991.
• Cheng, B.H., Software Engineering - CPS 470
  Class notes. Technical report, Michigan State
  University, 1997.