Other Data Models

Other Data Models

The entity-relationship and relational models are just two of the models that have importance in database systems today. In this section we shall introduce you to various other models of rising importance.

Review of Object-Oriented Concepts

Before introducing object-oriented database models, let us review the main object-oriented concepts themselves. Object-oriented programming has been extensively regarded as a tool for better program organization and, finally, more reliable software implementation.

The Type System

An object-oriented programming language offers the user a rich collection of types. Starting with atomic types, such as integers, real numbers, booleans, and character strings, one may construct new types by using type constructors. Usually, the type constructors let us

Introduction to ODL

ODL (Object Definition Language) is a standardized language for specifying the structure of databases in object-oriented terms. It is an extension of IDL (Interface Description Language), a component of CORBA (Common Object Request Broker Architecture). The latter is a

Attributes in ODL

The simplest type of property is the attribute. These properties explain some feature of an object by connecting a value of a fixed type with that object. For instance, person objects might each have an attribute name whose kind is string and whose value is the name of that

Relationships in ODL / Inverse Relationships

While we can learn much about an object by examining its attributes, often a critical fact about an object is the way it connects to other objects in the same or another class.

Multiplicity of Relationships

Like the binary relationships of the E/R model, a pair of inverse relationships in ODL can be classified as either many-many, many-one in either direction, or one-one. The type declarations for the pair of relationships tells us which.

Methods in ODL

The third kind of feature of ODL classes is the method. As in other object-oriented languages, a method is a piece of executable code that may be applied to the objects of the class.

Types in ODL

ODL gives the database designer a type system similar to that found in C or other usual programming languages. A type system is built from a basis of types that are described by themselves and certain recursive rules whereby complicated types are built from simpler types. In

Additional ODL Concepts

There are many other features of ODL that we must study if we are to express in ODL the things that we can express in the E/R or relational models. In this section, we shall cover:

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