Re: how is oracle 8.0 OODB?
Date: Tue, 26 May 1998 18:42:31 GMT
Message-Id: <slrn6mm3ec.55u.joelga_at_pebble.org>
On Mon, 25 May 1998 19:59:24 -0400, Manmeet S. Virdi <manmeet_at_bellatlantic.net> wrote:
>I am wondering how is Oracle 8.0 they call it OO? Is it really Object
>Oriented or they fake it? in the sense they use some sort of layer to
>make it look like OO?
>
>Does anyone has any clue on it?
Here's a little something they had on their web site:
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This document is part of a series of documents that are created to help users become familiar with new Oracle8 functionality. These documents are not meant to be comprehensive bulletins so much as flashes about matters of interest.
Basics of the Object Option
The Objects Option makes Oracle an object-relational database management system (ORDBMS). This means that users can define additional kinds of data - specifying both the structure of the data and the ways of operating on it - and use these types within the relational model. This option is built into the database in Oracle8. If users wish to use the Oracle8 database as a purely relational database, they can simply ignore the Object aspect. However, if they want to take advantage of Object features in a relational environment, they can.
Oracle8 with Object option stores data in its natural form and allows applications to work with it by using Object-oriented technology.
The new words in "Object Talk" are:
.Object type
.Class
.Instance
.Subclass
.Inheritance
.Polymorphism
.Encapsulation
.Method
Object Type
An object type is a person, place or a thing that has attributes. Female, City, Car etc are examples of Objects. In relational term, an object is like a row in a table.
Object Table
In order to have Oracle assign an object identifier to an object, the object must reside in a special kind of table called an Object Table.
Example
-------
Create type yellowpages AS OBJECT (
name varchar2(30),
phone varchar2(20));
AS OBJECT is required when creating an object type.
Create table phonebook of yellowpages;
The Object table phonebook holds phone numbers of type yellowpages.
Class
A class is the factory which creates an object. The oracle term for Class is 'Object Type' as mentioned above. The terms Class and Object type are often used interchangeably. In relational term, class is like a table definition.
Instance
An instance is an object that belongs to a particular class.
Mary is an instance of female object type.
Subclass
Any class can be specialized by creating subclass, that will inherit all the previously defined properties of the superclass. A racing car could be a subclass of class car.
Inheritance
Inheritance allows objects to use behaviour and attributes in classes above them in the hierarchy. A racing car could inherit all the attributes of class car.
Inheritance (the ability to subclass) is not available currently in 8.0, but is planned in a future release. A related feature is Object Views, which allows reuse of any defined Oracle8 type for any mix of legacy data in relational tables and object data in object tables... Using INSTEAD-OF triggers we can do all DML (INSERTs, UPDATEs, DELETEs) through those Object Views. Oracle8 is unique in having object views among the Object-Relational databases.
Method
A method is an operation taken on the object's data. Calculate the square root of a number is a method that can be shared by different objects.
Polymorphism
Polymorphism allows the same operation to be performed on objects of different classes with different effects i.e a Draw method could draw a polygon or an ellipse.
Encapsulation
Encapsulation protects objects by controlling how they are accessed It hides the low level implementation details. Methods can encapsulate objects by allowing only certain types of access.
Encapsulation is not currently part of the 'objects option' in 8.0. You cannot set visibility levels like public/private/protected for attributes or methods of an Oracle8 type. It is being considered for future releases.
You can read more about Object Option features in the Oracle8 Server Concepts Manual and the Oracle8 Server Application Developer's Guide.
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>Manmeet S. Virdi
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-- These opinions are my own and not necessarily those of Information Quest or Pebble In The Sky http://www.informationquest.com http://ourworld.compuserve.com/homepages/joel_garry jgarry_at_nospameiq.com "See your DBA?" I AM the _at_#%*& DBA! Remove nospam to reply. Sorry.Received on Tue May 26 1998 - 20:42:31 CEST