Object Orientation

1
Object Orientation
WHY Try to model the data, not the
tasks/procedures Data change less often! Data
is considered to be objects...
Some more of the (claimed) benefits of using
OOAD methods

• Increased abstraction
• Encouragement of cyclic development easy to
  revisit early stages
• OAD uses a core set of models
• OOAD increases software reusability,
• due to high degree of modularity

2
Objects Classes
An abstraction of something in a problem domain,
reflecting the capabilities of the system to
keep information about it, interact with it, or
both objects have crisp boundaries and
meaning for the problem at hand. They encapsulate
state and behaviour.
The state of an object is represented by
attributes and relationships. Behaviour is
represented by operations, methods and state
machines.
An object represents a particular instance of a
class. A class is a description of a set of
objects that share the same attributes,
operations, methods, relationships and semantics.
3
Capturing User Requirements Use Case Modeling in
UML (1/2)
A use case model employs actors and use cases
in order to depict a scenario of the systems
use.
Use case a part of the systems functionality.
Use case models can model functionality of
entities at different levels of abstraction
Use case models can be used for

• Illustration
• Validation
• System testing

4
Actors Use Cases

• The use case modeling is the technique during
  which use case models are produced. A use case
  model employs actors'' and use cases'' in
  order to depict a scenario of the system's use.
• The actors'' represent roles played by various
  people or other systems, while the use cases''
  represent typical interactions that the actor has
  with the system.
• Actor a coherent set of roles that users of use
  cases play when interacting with these use cases.
  An actor has one role for each use case with
  which it communicates''
• Use case the specification of a sequence of
  actions, including variants, that a system (or
  other entity) can perform, interacting with
  actors of the system'' OR
• a behaviourally related sequence of transactions
  in a dialogue with the system''

5
Capturing User Requirements Use Case Modeling in
UML (2/2)
What use case modeling is

• It is about what the system will do at a
  high-level, with respect to its users.

• It is about describing the system goals

• It is about capturing the functional requirements

What use case modeling is not

• It is not about capturing how the system will do
  anything

• It is not about describing the system functions.

To decompose or not to decompose? Tradeoffs
6

• Kenworthy E. Use Case Modelling Capturing
  User Requirements,
• http//www.zoo.co.uk/z0001039/PracGuides/pg_use_c
  ases.htm, December, 1997.
• M. Fowler K.Scott Use Cases,
• http//www2.awl.com/cseng/titles/0-20189542-0/tech
  niques/useCase.htm
• Sjaak Brinkkemper, Shuguang Hong, Arjan
  Bulthuis, Geert van den Goor
• Object-Oriented Analysis and Design Methods A
  Comparative Review,
• http//wwwis.cs.utwente.nl8080/dmrg/OODOC/oodoc/
  oo.html, January 1995
• Penker M. The Unified Modeling Language,
• http//www.boldsoft.com/news/columns/co
  lumn1998july.htm,
• July 1998.

7
Polymorphism(the ability to appear as many forms)
...In one of the StarTrek movies, Cap. Kirk was
in trouble, as usual. He met an extremely
beautiful lady who however thereupon changed
into a hideous troll. Kirk was quite surprised,
but the lady told him Didn't you know I am a
polymorph?''

• Polymorphism allows a message to achieve the
  same result, even when the mechanism for
  achieving it differs between different objects.
• Identical messages are sent to objects of
  different classes each object responds in a
  different, yet appropriate way.
• The requesting object need not know the class of
  the receiving object.