Object (computer science)

In computer science, an object can be a variable, a data structure, a function, or a method, and as such, is a value in memory referenced by an identifier. In computer science, an object can be a variable, a data structure, a function, or a method, and as such, is a value in memory referenced by an identifier. In the class-based object-oriented programming paradigm, object refers to a particular instance of a class, where the object can be a combination of variables, functions, and data structures. In relational database management, an object can be a table or column, or an association between data and a database entity (such as relating a person's age to a specific person). An important distinction in programming languages is the difference between an object-oriented language and an object-based language. A language is usually considered object-based if it includes the basic capabilities for an object: identity, properties, and attributes. A language is considered object-oriented if it is object-based and also has the capability of polymorphism and inheritance. Polymorphism refers to the ability to overload the name of a function with multiple behaviors based on which object(s) are passed to it. Conventional message passing discriminates only on the first object and considers that to be 'sending a message' to that object. However, some OOP languages such as Flavors and the Common Lisp Object System (CLOS) enable discriminating on more than the first parameter of the function. Inheritance is the ability to subclass an object class, to create a new class that is a subclass of an existing one and inherits all the data constraints and behaviors of its parents but also adds new and/or changes one or more of them. Object-oriented programming is an approach to designing modular reusable software systems. The object-oriented approach is an evolution of good design practices that go back to the very beginning of computer programming. Object-orientation is simply the logical extension of older techniques such as structured programming and abstract data types. An object is an abstract data type with the addition of polymorphism and inheritance. Rather than structure programs as code and data, an object-oriented system integrates the two using the concept of an 'object'. An object has state (data) and behavior (code). Objects can correspond to things found in the real world. So for example, a graphics program will have objects such as circle, square, menu. An online shopping system will have objects such as shopping cart, customer, product. The shopping system will support behaviors such as place order, make payment, and offer discount. The objects are designed as class hierarchies. So for example with the shopping system there might be high level classes such as electronics product, kitchen product, and book. There may be further refinements for example under electronic products: CD Player, DVD player, etc. These classes and subclasses correspond to sets and subsets in mathematical logic. An important concept for objects is the design pattern. A design pattern provides a reusable template to address a common problem. The following object descriptions are examples of some of the most common design patterns for objects. The object-oriented approach is not just a programming model. It can be used equally well as an interface definition language for distributed systems. The objects in a distributed computing model tend to be larger grained, longer lasting, and more service-oriented than programming objects. A standard method to package distributed objects is via an Interface Definition Language (IDL). An IDL shields the client of all of the details of the distributed server object. Details such as which computer the object resides on, what programming language it uses, what operating system, and other platform specific issues. The IDL is also usually part of a distributed environment that provides services such as transactions and persistence to all objects in a uniform manner. Two of the most popular standards for distributed objects are the Object Management Group's CORBA standard and Microsoft's DCOM.