Architecture

ObjectDRIVER is a middleware tool with which one can create an ODMG compliant Object Oriented Database Management Systems (OODBMS) on top of heterogeneous Relational Database Management Systems (RDBMS). It offers C++ and Java language bindings and an Object Query Language (OQL) interface. ObjectDRIVER is particularly well suited to:

   1. Reuse of existing databases:

      Many existing information systems store data using schema that cannot be modified. Thus, ObjectDRIVER provides a very powerful tool which enables the design of new applications without the need to change the existing system.

   2. Addition of persistence to Object Oriented applications:

      Given the description of an application's class hierarchy, ObjectDRIVER can automatically create the corresponding relational schema. In this case, the application and the user don't have to be concerned with how the data is stored and retrieved. ObjectDRIVER acts as an efficient object repository, using underlying RDBMS as intelligent file systems.

Compared to the exclusive use of an OODBMS, there are numerous benefits of choosing ObjectDRIVER as a middle tier approach:

- Firstly, the application designer himself defines the object models to be handled. Thus, unlike other Relational to Object tools, the underlying databases are directly viewed through the object model defined by the designer.

- Secondly, ObjectDRIVER gives access to an enormous amount of data. Since industry has invested in relational databases for a long time, the relational model is by far the most widely used standard across the DBMS world. In addition, object technologies have become a standard for applications development. Consequently, many people want to use object technologies without having to sacrifice existing applications and DBMS. This leads to the well known impedance mismatch problem, where the DBMS metamodel differs from the current metamodel for application development. ObjectDRIVER provides the solution to this problem, allowing object oriented applications to be designed on top of the existing DBMS, without changing the way anything is organized. In fact, from the DBMS point of view, ObjectDRIVER can just be considered as another client.

- Last but not least, the use of ObjectDRIVER offers a complete and clear separation between the Object level, i.e. the knowledge representation level, and the physical level, i.e. the data management level.

Key concept

The key concept of ObjectDRIVER is the notion of mapping. Using a generic correspondence language, one can easily define a hierarchy of classes above relational tables. A class can be defined by a set of constraints above a set of relational tables.

Once a class hierarchy has been defined, the "relational aspects" of data are hidden to the user or the applications. One can see the data, just as if they were stored in an ODMG compliant Object Oriented DBMS. ObjectDRIVER is now ready to handle all the laborious activity of sending SQL requests to the database (Select, Insert, Update, Delete) in place of the application, and to build the object information as expected by the applications. Furthermore, the Java and C++ bindings provide a way to create new, ODMG compliant Object oriented applications, without having to modify the underlying DBMS.

The query language implements most of the functionality defined by ODMG for OQL. Furthermore, any access to the underlying database is made through an ODBC layer which makes ObjectDRIVER work on top of the vast majority of commercial RDBMS.

ObjectDRIVER supports multithreading and allows concurrent applications to access in parallel the same or different relational databases. Currently, one application can send requests to many databases at the same time. However, is not possible yet to merge data issued from different database. This feature in addition to support for XML and HTML languages will be available with the coming versions of ObjectDRIVER. Subscribe to Infobjects' Newsletter or enter the ObjectDRIVER's Newsgroup now to be informed in advance of latest improvements in the product.