A Brief Overview of the Unified Modeling Language

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A Brief Overview of the Unified Modeling Language

• Bran SelicObjecTime Limited
• bran_at_objectime.com

Rev.2
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Overview

• Introduction
• The Object Paradigm
• Modeling with the UML
• Summary

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What is the UML?

• General-purpose OO modeling language
• convergence of a number of popular OO methods

Catalysis
ROOM
etc.
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Inside the Standard

• Semi-formal semantic meta model
• defines the basic modeling concepts
• object, class, association, etc.
• includes formal well-formedness rules expressed
  as constraints in the Object Constraint Language
  (OCL)
• Graphical notation for modeling concepts
• 8 different diagram types
• Two predefined domain extensions

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• Introduction
• The Object Paradigm
• Modeling with the UML
• Summary

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A Brief History of Objects

• 1967 Simula programming language
• 1970s Smalltalk programming language
• 1980s Theoretical foundations, C,
  Objective-C, etc.
• 1990s Object-oriented analysis and design
  methodologies (Booch, OMT, ROOM, etc.), Java
• 1997 The Unified Modeling Language (UML)
  standardized by the Object Management Group (OMG)

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The Object Paradigm

• A synergistic combination of various proven
  techniques including
• encapsulation
• inheritance
• polymorphism/genericity
• Salient characteristic a software system is
  rendered as a structure of collaborating parts
• the object paradigm is inherently structural

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Structure

• The individual parts of a system and their
  run-time topological relationships
• Fundamental structural relationship types

• Containment (strong and weak)

composition (strong)
aggregation (weak)

• Layering

• Communication (links)

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Objects

• Entities that model some physical or conceptual
  entity
• a unique identity (dedicated memory)
• the conceptual becomes physical!

• a public interface

• a hidden (encapsulated) implementation

methods
public attributes
Telephone1
busy boolean
public operations
offHook() onHook () ring()
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Conceptual Objects

• Not all objects necessarily require a physical
  underpinning
• For example, the telephone call object

abortCall () addParty (tTelephone) reportDuration
()
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Classes and Instances

• Design-time specifications for one or more
  distinct objects with a common form (structure
  and behavior)

instance (run time)
class (design time)
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Object Behavior

• Simple basic reactive server model

InitializeObject
Handling depends on specific request type and
object state
Wait forRequest
HandleRequest
Invokes operations on other objects
TerminateObject
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Programming Model

• Combining objects into object structures

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Object Engines

• Passive objects depend on external motive power
  (e.g., main program thread)

• Active objects self-powered (own thread of
  execution)

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Inheritance and Polymorphism

• Generalization and re-use mechanisms

Generalization (inheritance) association
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• Introduction
• The Object Paradigm
• Modeling with the UML
• Summary

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Why Build Models?

• To understand the problem better
• To communicate with stakeholders
• To find errors or omissions
• To plan out the design
• To generate code

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UML Model Views

• Requirements (use case diagrams)
• Static structure (class diagrams)
• kinds of objects and their relationships
• Dynamic behavior (state machines)
• possible life histories of an object
• Interactive behavior (activity, sequence, and
  collaboration diagrams)
• flow of control among objects to achieve
  system-level behavior
• Physical implementation structures (component and
  deployment diagrams)
• software modules and deployment on physical nodes

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Class Diagram - Static Structure

• Shows the entities in a system and their general
  relationships

association class
Person
generalization
association
residence
0..
ordered
House
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Object Instance Diagram

• Shows object instances in a particular case

link
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State Machine Diagram

• Each state corresponds to a selective receive
  action

state machine
initial state
state
trigger
action expression
final state
transition
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State Machine Behavior

• Event handling details depend on state

start/master.ready()
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Active Objects in the UML

• Concurrent incoming events are queued and handled
  one-at-a-time regardless of priority
• run-to-completion (RTC) execution model

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RTC and Concurrency

• Eliminates need to write complex and error-prone
  synchronization code
• if all passive objects encapsulated by an active
  object, only a single thread can pass through
  each passive object

passive encapsulated objects (protected
attributes)
The event handler is an implicit critical region
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RTC Semantics

• RTC step semantics must not be confused with
  uninterruptibility or unpre-emptabilty
• interrupts do not have to be blocked
• an active object can be pre-empted by another
  active object responding to a higher-priority
  event
• priority inversion only occurs when an active
  object blocks itself (i.e. it cannot block any
  other active object)
• The effectiveness of this is supported by the
  following empirical results
• most event handling is trivial
• in computer terms, events occur infrequently

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State-Based Actions

• Entry action executed whenever a state is
  (re-)entered
• Exit action executed whenever a state is
  departed
• Internal transition a self transition executed
  without leaving and re-entering a state

entry/m.entered() exit/m.departed() poll/m.ack
()
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Hierarchical States and Transitions

• Allows step-wise refinement and viewing of
  complex behavior

group transition
default transition
composite state
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Signals

• Used for asynchronous communication
• specified by a special type of class

• can be organized into class hierarchies

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Sequence Diagrams

• Assertions of legal interactions between objects
  (e.g., operator-assisted call)

sequence diagram
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Collaboration Diagram

• Show generic structure and behavior

classifier role
P2TTSet
P1BusSet
P2TTSet
P1BusSet
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• Introduction
• The Object Paradigm
• Modeling with the UML
• Summary

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Summary the UML

• An industry standard for analysis and design of
  object-oriented systems
• based on extensive experience and best practices
• gaining rapid acceptance (training, tools, books)
• Comprises
• set of modeling concepts
• graphical notation
• Leaf concepts organized into 8 diagram types
• class, state machine, collaboration, use case,
  sequence, activity, component, deployment
• The UML can be used in many different domains to
  capture domain-specific concepts and ideas