CS551 UML for Distributed Objects Chapter 2 of Engineering Distributed Objects

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CS551UML for Distributed Objects (Chapter 2 of
Engineering Distributed Objects)

• Yugi Lee
• STB 555
• [phone]
• yugi_at_cstp.umkc.edu
• www.cstp.umkc.edu/yugi

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UML and Meta Model for Distributed Objects

• Used for communicating about objects
• Static vs. dynamic properties
• Type vs. instance properties
• UML
• Use Case Diagrams
• Sequence Diagrams
• Class and Object Diagrams
• State Diagrams
• Packages
• Meta Model

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Use Case Diagrams
Plan Training
Trainer
Schedule
Determine League
Games
National Soccer
Manager
Association
Print Personal
Player
Schedule
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Sequence Diagrams
BvBTeam
TeddyPlayer
StefanPlayer
Output
TonyTainer
bookGoalies
book()
book()
printTrainingPlan
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Class Diagrams
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Packages
Soccer Clubs
League
Management
National Team
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Object Diagrams
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State Diagrams
in team
healthy
in match
playing
/swap
/swap
/injury
reserve
injured
in_squad /play
!in_squad /play
/recovered
/finish
/finish
free
training
/exercise
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Parallel State Composition
Player
/sign_contract
/unsatisfaction
happy
on transfer list
/resign
in team
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Meta Model for Distributed Objects

• Distributed Systems consist of multiple
  components.
• Components are heterogeneous.
• Components still have to be interoperable.
• There has to be a common model for components
  that expresses
• component states,
• component services and
• interaction between components.

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OO Approach to Distributed Systems

• Components ? objects.
• Visible component state ? object attributes.
• Usable component services ? object operations.
• Component interactions ? operation execution
  requests.
• Component service failures ? exceptions.

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Need for an Object Meta-model

• There are many different object-oriented
  approaches
• Distribution middleware must define object model
  that can serve as a common basis for
  heterogeneous components.
• We introduce general distributed object model to
  capture common characteristics of object models
  of different distributed object-middleware.

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Different levels of abstraction...
Meta-Object Facility
Level 3
Meta Object Model
Level 2
Object Types
Level 1
Objects
Level 0
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Object

• Has a unique identifier.
• May have many different references that refer to
  the object.
• Has a set of attributes whose names denote
  values.
• References may denote
• equal objects
• identical objects
• Is encapsulated by operations.
• May raise particular exceptions.

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Sample Object
klinsiPlayer
name Jürgen Klinsmann role Forward Number
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Types and Distributed Objects

• Attributes, operations and exceptions are
  properties objects may export to other objects.
• Multiple objects may export the same properties.
• Only define the properties once!
• Attributes and operations, and exceptions are
  defined in object types.

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Attributes

• Attributes have a name and a type.
• Type can be an object type or a non-object type.
• Attributes are readable by other components.
• Attributes may or may not be modifiable by other
  components.
• Attributes correspond to one or two operations
  (set/get).

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Exceptions

• Service requests in a distributed system may not
  be properly executed.
• Exceptions are used to explain reason of failure
  to requester of operation execution.
• Operation execution failures may be
• generic or
• specific.
• Specific failures may be explained in specific
  exceptions.

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Operations

• Operations have a signature that consists of
• a name,
• a list of in, out, or in-out parameters,
• a return value type, and
• a list of exceptions that the operation can raise.

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Object Type Example
ltltinterfacegtgt Player
-namestring -rolePosition -Numberint
void book(in Date d) raises (AlreadyBooked)
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Operation Execution Requests

• A client object can request an operation
  execution from a server object.
• Operation request is expressed by sending a
  message (operation name) to server object.
• Server objects are identified by object
  references.
• Clients have to react to exceptions that the
  operation may raise.

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Subtyping

• Properties shared by several types should be
  defined only once.
• Object types are organised in a type hierarchy.
• Subtypes inherit attributes, exceptions and
  operations from their supertypes.
• Subtypes can add more specific properties.
• Subtypes can redefine inherited properties.

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Multiple Inheritance

• Means that one object type can be subtype of more
  than one super type
• Not supported by all middleware
• May lead to ambiguities

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Multiple Inheritance Example
ltltinterfacegtgt Player
ltltinterfacegtgt Trainer
-namestring -rolePosition -Numberint
-salaryint
void book(in Date d) raises (AlreadyBooked) nex
t_game()Date
next_game()Date
ltltinterfacegtgt PlayerTrainer
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Polymorphism

• Object models may be statically typed.
• Static type of a variable restricts the dynamic
  type of objects that can be assigned to it.
• Polymorphism denotes the possibility of
  assignments of objects that are instances of the
  static type and all its subtypes.

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Polymorphism Example
chelseaTeam
name Chelsea
vPlayerTrainer
dPlayer
name Gianluca Vialli role Forward Number
10 salary1000000
name Marcel Desailly roleDefender Number5
zPlayer
name Gianfranco Zola roleForward Number3