Object-Oriented Features in Oracle

In this chapter, we will describe Oracle™ features that can be used to support the implementation of an object-oriented model. As an overview, Section 2.1 will outline some of the original features within a standard relational model. The next sections will illustrate the additional object-oriented features. We will use these new features for our implementation in the subsequent chapters.

Generic Methods

Generic methods are the methods used to access the attributes of an object. The concept behind the need for generic methods is encapsulation, in which attributes associated with an object can be accessed directly only by the methods within the object itself. Therefore, each time an attribute is created within an object, we will need generic methods to access the attribute. This is the main difference between the standard relational techniques for implementing operations vs. the object-oriented methods. In relational databases, users normally can directly access attributes of a table by running SQL statements to update, delete, or insert. This may generate problems when certain attributes within an object have some constraints applied to them, and therefore the ad hoc access may violate these constraints.

Object-Oriented Methods

We recall that an object-oriented model consists of two major aspects: the static and dynamic. The former covers the implementation of the data structure, which includes the object’s attributes and relationships, whereas the latter is concerned with the object’s operations, which is the implementation of object-oriented methods using SQL and PL/SQL. The static and dynamic parts of an object model actually form a nonseparated unit since accesses to the attributes of an object must be done through the available methods. This raises the concept of encapsulation.

Using Object-Oriented Features

In Chapter II, we discussed the different features available in Oracle™ that can be used to implement an object-oriented model. We will use those features in this chapter. The discussion in this chapter will be categorized based on the relationship types. There are three distinct relationship types that we have to consider in object-oriented modeling for implementation in object-relational databases: inheritance, association, and aggregation. Some manipulations will be needed in order to accommodate the features of these relationships.

Retailer Case Study

In this chapter we will demonstrate the usage of development tools provided by Oracle™ Developer. The tools help users create forms, queries, projects, and other applications needed for practical purposes. Notice that we use Oracle™ Developer 6.0 for this chapter. Newer versions will have more features. Before demonstrating the usage of Oracle™ Developer, we will present another case study whose database has to be developed first.

University Case Study

Our intention in the previous chapters was to give some understanding of the ORDB concept and its implementation using Oracle™. Examples, case studies, and questions based on these chapters have been relatively simplified in order to explain one concept at a time. However, in the real world, often we find far more complex cases that may involve the integration of every concept that we have already discussed. In this chapter, we will consider a bigger case study that uses most of the ORDB concepts. In addition, we will also demonstrate the implementation of a big case study into one application that can be more user friendly. For this purpose, we will use a package that is also provided by Oracle™.

User-Defined Queries

This chapter describes object-based user-defined queries in Oracle™. The queries will vary based on the hierarchy of the object model. We will show different categories of queries along the object-oriented relationships of inheritance, association, and aggregation. These queries can be performed as ad hoc queries or implemented as methods. User-defined methods are methods whereby users define algorithms or the processes to be carried out by the methods. Since these methods involve operations specified by the users, they are called user-defined methods. As an example, we will use the case study of the authorship of the course manual in Chapter III as a working example for this chapter. Some queries discussed here are based on the DDL specified in Figure 3.36.

Object-Related Approaches

This book focuses on the implementation of an object-oriented model into object-relational DBMS using Oracle™. All aspects of the object-oriented model, particularly those that play a significant role in database implementation, will be discussed in this book. The object-oriented modeling technique is an important issue in this book because it is the underlying notion behind the development of the object-relational approaches. Therefore, in this chapter we will start with an outline of the object-oriented conceptual model (OOCM).