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Chapter 3: Oracle8i and Object Relational Technology
What Is an Object-Oriented Database?As we have all heard many times before, Oracle 8.0 was Oracle's first version of the database to incorporate object-oriented technology, and thus Oracle 8.0 was the corporation's first object-relational database. Notice we used the term object-relational database because this implementation is not a pure object-oriented database, nor is it just a relational database. It now represents a hybrid of the two, so let's call it an obiect-relational database.
Today, Oracle has won over the enterprise. People already see Oracle as a mission-critical database able to get them the results they need. People are very comfortable with the technology they bring to the corporate world. Their preference will be to go with the Oracle implementation of the relational database as long as they can bring the key features of object-oriented technologies. Well, Oracle8i represents just that. At this point, we feel they have won the battle and the war. It's also interesting to note that many industry leaders would now concur with this.
To help you appreciate and understand what Oracle8i means to the industry and why object- relational databases will become the standard, we will first discuss object-oriented technologies and then provide an overview of Oracle8i and its key changes.
Unlike the relational database approach-which deals with data at the lowest possible level, a series of columns and rows-the object-oriented approach deals with data at a much higher level; it deals with the objects surrounding the data. In an object-oriented database, when dealing with the customer, you deal with an object called "customer." When dealing with an order, you reference an object called "order." Since an object database understands the object customer and all its relationships, it can easily deal with the object customer and all that is needed to work with it.
in the relational model, order is really a combination of many different tables, with intersection tables holding all the attributes needed to support and maintain an order. In the object model, the database has intelligence about the interrelationships. This is not the case in the relational model. When a change is made to the relational model, it usually translates into a whole new series of tables that must be developed if the model is to continue to work. These relationships must be recrafted by a database designer.
Let's take a closer look at when a customer places an order in a relational database. A number of tables are needed to support that activity. There may be a customer table, an inventory table, a price table, an inventory-price table, a line_item_table, a customer-history table, and so on. in order to manipulate these tables, the programmer must craft the needed code with the required links between tables.
As you can see, the simple act of placing an order requires a number of tables. Rows and columns in tables contain information required for the assembly of the order. A single change to the order process can have a major impact on the underlying tables that support it, requiring a database designer to come in to craft the new relationships and their associated tables to represent those relationships. In the object-oriented model, this is not the case. In fact, it assumes that these relationships will change, and that change is just a natural occurrence and progression.
What Is an Object?
Objects are software representations of real-world entities. To capture the features and capabilities of the real world, objects consist of both attributes and operational information. Remember, in an object-oriented database, the data dictionary not only stores (and allows you to understand) the relationship of one object to another, but also understands the behaviors of the object.
What Is a Class?
When objects are similar to one another in behaviors and other attributes, they can be put together into a class. This concept of classes, parent classes, subclasses, and superclasses allows for a level of abstraction for grouping objects. Think of a class as a template for objects. This helps you in managing very complex objects. This capability to group by class also allows objects to take advantage of similarities of behaviors and other characteristics they share.
Encapsulation
One of the basics of the object-oriented model is the support of encapsulation. Encapsulation is when the data is bound to the object so that access to the data can only happen through the behaviors approved or accepted by that object. This has the direct benefit of protecting the data from illegal access....