Data definition language ddl 2 data manipulation

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Unformatted text preview: entional database models, makes database implementation of many applications inconvenient. The object-oriented database model was introduced to overcome the above listed shortcomings of conventional database models. A data model is a logical organization of the real-world objects (entities), constraints on them, and relationships among objects. A database model that captures object-oriented concepts such as class hierarchy, inheritance, and methods is ah object-oriented database model. An object-oriented database is a collection of objects whose behavior and state, and the relationships are defined in accordance with an objectoriented database model. An object-oriented database management system is one, which allows the definition and manipulation of an object-oriented database. The object-oriented database model is the preferred model for a large range of database applications such as CAD, CAE, CAM, CASE, expert systems, and multimedia systems. The reason is that object-oriented concepts already include such data modeling concepts as grouping of objects into a class, aggregation relationships between an object and other objects it consists of (nested objects), and generalization relationships between a class of objects and classes of objects specialized from it. The fact that an object-oriented database model includes the aggregation and generalization relationships means that an object-oriented database management system provides direct support for the definition and manipulation of the relationships among objects. This in turn means that application programmers need not explicitly program and manage these relationships. An example of an object-oriented database structure is shown in Figure 16.11. The class Vehicle is the root of a class-composition hierarchy, which includes the classes VehicleSpecs, Company, and Employee. The class Vehicle is also the root of a class hierarchy involving the classes TwoWheeler and FourWheeler. The class Company is in turn the root of a class hierarchy with subclasses DomesticCompany and ForeignCompany. It is also the root...
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