CSC/ECE 517 Fall 2007/wiki2 2 aa

Object-relational mapping. Ruby's ActiveRecord is one attempt to allow an object-oriented program to use a relational database. The Crossing Chasms pattern is another. Look up several approaches to mapping relational databases to o-o programs, include hyperlinks to all of them, and explain how they differ. Report on the strengths of various approaches (making sure to credit the authors for their insights).

Introduction

Object-oriented (o-o) programming uses Object to manage data. Objects have identity, state, and behavior, which means Object is focus on identity and behavior of the things in real world. However relational database is focus on information. It is a collection of relation variables between the attributes of tables, it describes the complete state of an information model.

For instance, a "Customer Object" in on line bookstore system implemented by o-o programming constains the information of the customer such as name, address, email, and phone number. It also constains some methods operated by customer, such as "ordering_books", which defines the ordering behavior of the customer.

However, the popular relational database, such as MS SQL products, can only stores and manipulate the information of the customer within table "Customer". The ordering behavior is not included in the "Customer" table.

Therefore, programmers have to transform values between object in o-o programming and relational database. Object-ralational mapping is introduced to solve this problem.

Object-relational Mapping

Object-relational mapping is a programming technique or process to transform data between relational database and a set of objects in object-oriented programming.

Implementations

ActiveRecord in Ruby

Ruby ActiveRecord maps the relational database tables with objects.

Comparison

In Hibernate, you'd usually begin development by working on your Java objects because Hibernate is a mapping framework. The object model becomes the center of your Hibernate universe. Active Record is a wrapping framework, so you start by creating a database table. The relational schema is the center of your Active Record universe. Active Record also includes some features that many Java frameworks don't have, such as model-based validation.Model-based validation lets you make sure the data within your database stays consistent.

Reference

1. Wikipedia Definition
2. Foundations of Object-Relational Mapping
3. ORM Thesis[1]
4. Crossing borders: Exploring Active Record

External Links

1. O/R Mapping Products

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