The Object Oriented Model
The object-oriented(OO) model actually had its beginning in the 1970s, but it did not see significant commercial use until the 1990s. This sudden emergence came from the inability of then existing RDBMSs (Relational Database Management Systems) to deal with complex data types such as images, complex drawings, and adio-video files. The sudden explosion of the Internet and the World Wide Web created a sharp demand for mainstream delivery of complex data.
An object is a logical grouping of related data and program logic that represents a real world thing, such as customer, employee, order or product. Individual data items such as customer ID and customer name, are called variables in the OO model and are stored within each object. In OO terminology, a method is a piece of application program logic that operates on a particular object and provides a finite function, such as checking customer’s credit limit or updating a customer’s address. Among the many difference between the OO models already represented the most significant variables may only be accessed through methods. This property called encapsulation.
The stict definition of object used here applies only to the OO model. The general term database object, refers to any named item that might be stored in a non-OO database(for example, a table, index, or view). As OO concepts that have found their way into relational database, so has the terminology, although often with less percise definitions
Figure 1.0 shows the customer object as an example of OO implementation.The circle of methods around the central core of variables in to remind us of encapsulation, In fact, you can think of an object must like an atom with an electron field of methods and a nucleus of variables. Each customer of Northwind should have its own copy of object structures, called an object instance, much as each individual customer has a copy of the customer...
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