OOAD Quick Guide
Object Diagrams, sometimes referred to as Instance Like class diagrams, they also show the relationship between objects but they use real world Click on the image to use the object diagram as a template. An introduction to object-oriented analysis and design. They represent things like employees, images, bank accounts, spaceships, The analysis phase identifies the objects, their relationship, and behavior using the. Object Oriented DBMS. B Level DOEACC Module 3 OO Data Model- OO Relationships. no profile picture user. Post. Be the first to comment.
As work progresses on the Use Cases, the requirements of the system become clearer enabling the Object Model to be updated in parallel, helping us make sure our model and the subsequent implementation in the chosen language contains all the necessary classes and class inter-links.
Whilst we're nearer to resolving some of the issues identified at the end of the discussion of implementing Object Models, a number are still outstanding: To sort out the remaining issues we'll need to look in more detail exactly how each Use Case will be implemented, using Sequence Diagrams. Figure 10 - Sequence Diagram for Overdrawn Report Performing a complete analysis requires that each individual Use Case must be examined, although in practise only selected Use Cases may be examined.
The Overdrawn Report Use Case is thus implemented as follows: The Head-Office object there is only one of them has methods which correspond to each Use Case - in this case an OverdrawnReport method this is a convenience for brevity, normally there would be a single "InitialObject" which the system would know about, and which would provide the entry point into the run-time model for all code.
The Branch object in turn passes the request on down to each Account it holds using the Account's OverdrawnReport method!
- OOAD - Object Model
OverdrawnReport method the detail of this is not shown - but involves summing up all the Transactions it holds, and checking the date on which it last became overdrawn. The method calls unwind until the Use Case is complete. OverdrawnReport methods have been added to the Branch and Account classes. A lastReportedDate attribute and associated methods have been added to the Account class, along with a printOverdrawnReport method.
The "administers" relationship between Head-Office and Branch has been qualified to indicate that "direct access" via the Branch's "sort-code" is required across the link thus assisting in link design - note the consequent change in the multiplicity of the relationship from many-to-one to one-to-one.
We have added directionality to many of the links e.
Of course, we've only looked at one Use Case, so its likely the model will change further as more sequence diagrams are developed. The Overall Process From the above discussion we can see that Use Cases and Sequence Diagrams both add to integrity and completeness of our Object Model, and that a good Object Model provides a firm foundation for a good design, and hence a good implementation of the system.
Problem Domain Analysis is concerned with capturing requirements and producing a first cut Object Model. Typically the Object Model will be incomplete, having only a subset of the class attributes and methods defined.
Problem Domain Design is concerned with finalising the detail of the problem domain parts of the Object Model, and results in an Object Model with a complete set of Problem Domain specific classes, attributes and methods.
UML - Object Diagrams
Objects can be modelled according to the needs of the application. An object may have a physical existence, like a customer, a car, etc. Class A class represents a collection of objects having same characteristic properties that exhibit common behavior.Object Oriented programming ( OOP ) :- What is Aggregation , Association and Composition ?
It gives the blueprint or description of the objects that can be created from it. Creation of an object as a member of a class is called instantiation.
Thus, object is an instance of a class. Generally, different objects of a class have some difference in the values of the attributes.
Attributes are often referred as class data. A set of operations that portray the behavior of the objects of the class. Operations are also referred as functions or methods. Example Let us consider a simple class, Circle, that represents the geometrical figure circle in a two—dimensional space.
Encapsulation and Data Hiding Encapsulation Encapsulation is the process of binding both attributes and methods together within a class. Through encapsulation, the internal details of a class can be hidden from outside. It permits the elements of the class to be accessed from outside only through the interface provided by the class. Data Hiding Typically, a class is designed such that its data attributes can be accessed only by its class methods and insulated from direct outside access.
It should instead be accessed through the methods setValues and getValues. Message Passing Any application requires a number of objects interacting in a harmonious manner. Objects in a system may communicate with each other using message passing.
Suppose a system has two objects: The object obj1 sends a message to object obj2, if obj1 wants obj2 to execute one of its methods. Message passing enables all interactions between objects. Message passing essentially involves invoking class methods. Objects in different processes can be involved in message passing.
Inheritance Inheritance is the mechanism that permits new classes to be created out of existing classes by extending and refining its capabilities. The subclass can inherit or derive the attributes and methods of the super-class es provided that the super-class allows so. Besides, the subclass may add its own attributes and methods and may modify any of the super-class methods.
Humans, cats, dogs, and cows all have the distinct characteristics of mammals. In addition, each has its own particular characteristics. The following figure depicts the examples of different types of inheritance.
Polymorphism Polymorphism is originally a Greek word that means the ability to take multiple forms. In object-oriented paradigm, polymorphism implies using operations in different ways, depending upon the instance they are operating upon. Polymorphism allows objects with different internal structures to have a common external interface. Polymorphism is particularly effective while implementing inheritance. Example Let us consider two classes, Circle and Square, each with a method findArea.
Though the name and purpose of the methods in the classes are same, the internal implementation, i. When an object of class Circle invokes its findArea method, the operation finds the area of the circle without any conflict with the findArea method of the Square class.
Generalization and Specialization Generalization and specialization represent a hierarchy of relationships between classes, where subclasses inherit from super-classes. Generalization In the generalization process, the common characteristics of classes are combined to form a class in a higher level of hierarchy, i.
Specialization Specialization is the reverse process of generalization. Here, the distinguishing features of groups of objects are used to form specialized classes from existing classes.
It can be said that the subclasses are the specialized versions of the super-class.
OOAD Object Model
The following figure shows an example of generalization and specialization. Links and Association Link A link represents a connection through which an object collaborates with other objects. Through a link, one object may invoke the methods or navigate through another object. A link depicts the relationship between two or more objects.
Association Association is a group of links having common structure and common behavior. Association depicts the relationship between objects of one or more classes.
OOAD - Quick Guide
A link can be defined as an instance of an association. Degree of an Association Degree of an association denotes the number of classes involved in a connection. Degree may be unary, binary, or ternary. A unary relationship connects objects of the same class. A binary relationship connects objects of two classes.
A ternary relationship connects objects of three or more classes. Cardinality Ratios of Associations Cardinality of a binary association denotes the number of instances participating in an association. Aggregation or Composition Aggregation or composition is a relationship among classes by which a class can be made up of any combination of objects of other classes. It allows objects to be placed directly within the body of other classes.
An aggregate object is an object that is composed of one or more other objects. Benefits of Object Model Now that we have gone through the core concepts pertaining to object orientation, it would be worthwhile to note the advantages that this model has to offer. It is easy to maintain. Suppose a module develops an error, then a programmer can fix that particular module, while the other parts of the software are still up and running.
It supports relatively hassle-free upgrades. It enables reuse of objects, designs, and functions. It reduces development risks, particularly in integration of complex systems.