Object relationship and association in ooad knis

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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. 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. 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.

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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.

In object-oriented software engineering, the software developer identifies and organizes the application in terms of object-oriented concepts, prior to their final representation in any specific programming language or software tools. Phases in Object-Oriented Software Development The major phases of software development using object—oriented methodology are object-oriented analysis, object-oriented design, and object-oriented implementation.

Object—Oriented Analysis In this stage, the problem is formulated, user requirements are identified, and then a model is built based upon real—world objects. The analysis produces models on how the desired system should function and how it must be developed.

The models do not include any implementation details so that it can be understood and examined by any non—technical application expert. Object—Oriented Design Object-oriented design includes two main stages, namely, system design and object design.

System Design In this stage, the complete architecture of the desired system is designed.

Association (object-oriented programming) - Wikipedia

The system is conceived as a set of interacting subsystems that in turn is composed of a hierarchy of interacting objects, grouped into classes. System design is done according to both the system analysis model and the proposed system architecture. Here, the emphasis is on the objects comprising the system rather than the processes in the system. Object Design In this phase, a design model is developed based on both the models developed in the system analysis phase and the architecture designed in the system design phase.

All the classes required are identified.

  • Association (object-oriented programming)

The associations between the identified classes are established and the hierarchies of classes are identified. Besides, the developer designs the internal details of the classes and their associations, i. Object—Oriented Implementation and Testing In this stage, the design model developed in the object design is translated into code in an appropriate programming language or software tool.

The databases are created and the specific hardware requirements are ascertained. Once the code is in shape, it is tested using specialized techniques to identify and remove the errors in the code. The essential features are relative to the context in which the object is being used. Encapsulation Encapsulation is the process of binding both attributes and methods together within a class.

The class has methods that provide user interfaces by which the services provided by the class may be used. Modularity Modularity is the process of decomposing a problem program into a set of modules so as to reduce the overall complexity of the problem. Modularity can be visualized as a way of mapping encapsulated abstractions into real, physical modules having high cohesion within the modules and their inter—module interaction or coupling is low.

Through hierarchy, a system can be made up of interrelated subsystems, which can have their own subsystems and so on until the smallest level components are reached. Hierarchy allows code reusability.

For example, a flower is composed of sepals, petals, stamens, and carpel. Typing According to the theories of abstract data type, a type is a characterization of a set of elements. In OOP, a class is visualized as a type having properties distinct from any other types. Typing is the enforcement of the notion that an object is an instance of a single class or type. It also enforces that objects of different types may not be generally interchanged; and can be interchanged only in a very restricted manner if absolutely required to do so.

The operation is checked only at the time of execution, as in the programming language Smalltalk. Concurrency Concurrency in operating systems allows performing multiple tasks or processes simultaneously.

When a single process exists in a system, it is said that there is a single thread of control. However, most systems have multiple threads, some active, some waiting for CPU, some suspended, and some terminated. Systems with multiple CPUs inherently permit concurrent threads of control; but systems running on a single CPU use appropriate algorithms to give equitable CPU time to the threads so as to enable concurrency.

In an object-oriented environment, there are active and inactive objects. The active objects have independent threads of control that can execute concurrently with threads of other objects. 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.

OOAD - Object Model

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.

OOAD Object Model

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. 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.