Object oriented design - AbsoluteAstronomy.com

Object-oriented design is the process of planning a system of interacting objects

Object-oriented programming

Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...

for the purpose of solving a software problem. It is one approach to software design

Software design

Software design is a process of problem solving and planning for a software solution. After the purpose and specifications of software are determined, software developers will design or employ designers to develop a plan for a solution...

Overview

An object

Object (computer science)

In computer science, an object is any entity that can be manipulated by the commands of a programming language, such as a value, variable, function, or data structure...

contains encapsulated data and procedures grouped together to represent an entity

Entity

An entity is something that has a distinct, separate existence, although it need not be a material existence. In particular, abstractions and legal fictions are usually regarded as entities. In general, there is also no presumption that an entity is animate.An entity could be viewed as a set...

. The 'object interface', how the object

Object (computer science)

In computer science, an object is any entity that can be manipulated by the commands of a programming language, such as a value, variable, function, or data structure...

can be interacted with, is also defined. An object-oriented program is described by the interaction of these objects. Object-oriented design is the discipline of defining the objects

Object (computer science)

In computer science, an object is any entity that can be manipulated by the commands of a programming language, such as a value, variable, function, or data structure...

and their interactions to solve a problem that was identified and documented during object-oriented analysis.

What follows is a description of the class-based

Class-based programming

Class-based programming, or more commonly class-orientation, refers to the style of object-oriented programming in which inheritance is achieved by defining classes of objects, as opposed to the objects themselves .The most popular and developed model of OOP is a class-based model, as opposed to an...

subset of object-oriented design, which does not include object prototype-based

Prototype-based programming

Prototype-based programming is a style of object-oriented programming in which classes are not present, and behavior reuse is performed via a process of cloning existing objects that serve as prototypes. This model can also be known as classless, prototype-oriented or instance-based programming...

approaches where objects are not typically obtained by instancing classes but by cloning other (prototype) objects.

Input (sources) for object-oriented design

The input for object-oriented design is provided by the output of object-oriented analysis. Realize that an output artifact does not need to be completely developed to serve as input of object-oriented design; analysis and design may occur in parallel, and in practice the results of one activity can feed the other in a short feedback cycle through an iterative process. Both analysis and design can be performed incrementally, and the artifacts can be continuously grown instead of completely developed in one shot.

Some typical input artifacts for object-oriented design are:

Conceptual model: Conceptual model is the result of object-oriented analysis, it captures concepts in the problem domain
Problem domain
A problem domain is the area of expertise or application that needs to be examined to solve a problem. A problem domain is simply looking at only the topics you are interested in, and excluding everything else. For example, if you were developing a system trying to measure good practice in...

. The conceptual model is explicitly chosen to be independent of implementation details, such as concurrency
Concurrency (computer science)
In computer science, concurrency is a property of systems in which several computations are executing simultaneously, and potentially interacting with each other...

or data storage.

Use case
Use case
In software engineering and systems engineering, a use case is a description of steps or actions between a user and a software system which leads the user towards something useful...

: Use case is a description of sequences of events that, taken together, lead to a system doing something useful. Each use case provides one or more scenarios
Scenario (computing)
In computing, a scenario is a narrative describing foreseeable interactions of types of users and the system. Scenarios include information about goals, expectations, motivations, actions and reactions...

that convey how the system should interact with the users called actors to achieve a specific business goal or function. Use case actors may be end users or other systems. In many circumstances use cases are further elaborated into use case diagrams. Use case diagrams are used to identify the actor (users or other systems) and the processes they perform.

System Sequence Diagram
System Sequence Diagram
In software engineering, a system sequence diagram is a sequence diagram that shows, for a particular scenario of a use case, the events that external actors generate, their order, and possible inter-system events....

: System Sequence diagram (SSD) is a picture that shows, for a particular scenario of a use case, the events that external actors generate, their order, and possible inter-system events.

User interface
User interface
The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...

documentations (if applicable): Document that shows and describes the look and feel
Look and feel
In software design, look and feel is a term used in respect of a graphical user interface and comprises aspects of its design, including elements such as colors, shapes, layout, and typefaces , as well as the behavior of dynamic elements such as buttons, boxes, and menus...

of the end product's user interface
User interface
The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...

. It is not mandatory to have this, but it helps to visualize the end-product and therefore helps the designer.

Relational data model (if applicable): A data model is an abstract model that describes how data is represented and used. If an object database
Object database
An object database is a database management system in which information is represented in the form of objects as used in object-oriented programming...

is not used, the relational data model should usually be created before the design, since the strategy chosen for object-relational mapping
Object-relational mapping
Object-relational mapping in computer software is a programming technique for converting data between incompatible type systems in object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language...

is an output of the OO design process. However, it is possible to develop the relational data model and the object-oriented design artifacts in parallel, and the growth of an artifact can stimulate the refinement of other artifacts.

Object-oriented concepts

The five basic concepts of object-oriented design are the implementation level features that are built into the programming language. These features are often referred to by these common names:

Object/Class
Object (computer science)
In computer science, an object is any entity that can be manipulated by the commands of a programming language, such as a value, variable, function, or data structure...

: A tight coupling or association of data structures with the methods or functions that act on the data. This is called a class, or object (an object is created based on a class). Each object serves a separate function. It is defined by its properties, what it is and what it can do. An object can be part of a class, which is a set of objects that are similar.

Information hiding
Information hiding
In computer science, information hiding is the principle of segregation of the design decisions in a computer program that are most likely to change, thus protecting other parts of the program from extensive modification if the design decision is changed...

: The ability to protect some components of the object from external entities. This is realized by language keywords to enable a variable to be declared as private or protected to the owning class.
Inheritance
Inheritance (computer science)
In object-oriented programming , inheritance is a way to reuse code of existing objects, establish a subtype from an existing object, or both, depending upon programming language support...

: The ability for a class to extend or override functionality of another class. The so-called subclass has a whole section that is derived (inherited) from the superclass and then it has its own set of functions and data.
Interface
Interface (computer science)
In the field of computer science, an interface is a tool and concept that refers to a point of interaction between components, and is applicable at the level of both hardware and software...

: The ability to defer the implementation of a method. The ability to define the functions or methods signatures without implementing them.
Polymorphism
Polymorphism in object-oriented programming
Subtype polymorphism, almost universally called just polymorphism in the context of object-oriented programming, is the ability to create a variable, a function, or an object that has more than one form. The word derives from the Greek "πολυμορφισμός" meaning "having multiple forms"...

: The ability to replace an object with its subobjects. The ability of an object-variable to contain, not only that object, but also all of its subobjects.

Designing concepts

Defining objects, creating class diagram
Class diagram
In software engineering, a class diagram in the Unified Modeling Language is a type of static structure diagram that describes the structure of a system by showing the system's classes, their attributes, operations , and the relationships among the classes.- Overview :The class diagram is the main...

from conceptual diagram: Usually map entity to class.

Identifying attributes
Attribute (computing)
In computing, an attribute is a specification that defines a property of an object, element, or file. It may also refer to or set the specific value for a given instance of such....

.

Use design patterns
Design pattern (computer science)
In software engineering, a design pattern is a general reusable solution to a commonly occurring problem within a given context in software design. A design pattern is not a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that...

(if applicable): A design pattern is not a finished design, it is a description of a solution to a common problem, in a context. The main advantage of using a design pattern is that it can be reused in multiple applications. It can also be thought of as a template for how to solve a problem that can be used in many different situations and/or applications. Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved.

Define application framework
Application framework
In computer programming, an application framework consists of a software framework used by software developers to implement the standard structure of an application for a specific development environment ....

(if applicable): Application framework is a term usually used to refer to a set of libraries or classes that are used to implement the standard structure of an application for a specific operating system. By bundling a large amount of reusable code into a framework, much time is saved for the developer, since he/she is saved the task of rewriting large amounts of standard code for each new application that is developed.

Identify persistent objects/data (if applicable): Identify objects that have to last longer than a single runtime of the application. If a relational database is used, design the object relation mapping.

Identify and define remote objects (if applicable).

Output (deliverables) of object-oriented design

Sequence Diagrams
Sequence diagram
A sequence diagram in Unified Modeling Language is a kind of interaction diagram that shows how processes operate with one another and in what order. It is a construct of a Message Sequence Chart....

: Extend the System Sequence Diagram
System Sequence Diagram
In software engineering, a system sequence diagram is a sequence diagram that shows, for a particular scenario of a use case, the events that external actors generate, their order, and possible inter-system events....

to add specific objects that handle the system events.

A sequence diagram shows, as parallel vertical lines, different processes or objects that live simultaneously, and, as horizontal arrows, the messages exchanged between them, in the order in which they occur.

Class diagram
Class diagram
In software engineering, a class diagram in the Unified Modeling Language is a type of static structure diagram that describes the structure of a system by showing the system's classes, their attributes, operations , and the relationships among the classes.- Overview :The class diagram is the main...

: A class diagram is a type of static structure UML
Unified Modeling Language
Unified Modeling Language is a standardized general-purpose modeling language in the field of object-oriented software engineering. The standard is managed, and was created, by the Object Management Group...

diagram that describes the structure of a system by showing the system's classes, their attributes, and the relationships between the classes. The messages and classes identified through the development of the sequence diagrams can serve as input to the automatic generation of the global class diagram of the system.

Some design principles and strategies

Dependency injection
Dependency injection
Dependency injection is a design pattern in object-oriented computer programming whose purpose is to improve testability of, and simplify deployment of components in very large software systems....

: The basic idea is that if an object depends upon having an instance of some other object then the needed object is "injected" into the dependent object; for example, being passed a database connection as an argument to the constructor instead of creating one internally.
Acyclic dependencies principle: The dependency graph of packages or components should have no cycles. This is also referred to as having a directed acyclic graph
Directed acyclic graph
In mathematics and computer science, a directed acyclic graph , is a directed graph with no directed cycles. That is, it is formed by a collection of vertices and directed edges, each edge connecting one vertex to another, such that there is no way to start at some vertex v and follow a sequence of...

. For example, package C depends on package B, which depends on package A. If package A also depended on package C, then you would have a cycle.
Composite reuse principle
Composite reuse principle
Composition over inheritance in object-oriented programming is a technique by which classes may achieve polymorphic behavior and code reuse by containing other classes which implement the desired functionality instead of through inheritance....

: Favor polymorphic composition of objects over inheritance.

External links

Object-Oriented Analysis & Design - overview using UML
Larman, Craig. Applying UML and Patterns - Third Edition
Object-Oriented Analysis and Design
LePUS3 and Class-Z: formal modelling languages for object-oriented design

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Overview

Input (sources) for object-oriented design

Object-oriented concepts

Designing concepts

Output (deliverables) of object-oriented design

Some design principles and strategies

See also

External links