What Are Data Cartridges?

Within the framework of the Oracle Extensibility Architecture, data cartridges are the mechanism for extending the capabilities of the Oracle server. What does this mean?

First, Oracle8i lets you capture the business logic and processes associated with domain-specific data in user-defined datatypes. In some cases, where the data cartridge provides new behavior without needing new attributes, the vehicle of implementation may be packages rather than formal types. Once you have defined these types using either of these approaches, Oracle8i allows you to determine the manner in which the server interprets, stores, retrieves, and indexes the data. Ultimately, data cartridges are the means to package this functionality as software components that can then be plugged into a server to extend its capabilities into a new domain.

This is all possible because the database has itself been made extensible. That is, you can now customize the database management system so that it treats user-defined business objects and rich types on a par with native types with regard to server mechanisms such as indexing and query optimization. Where some aspects of a native service is not adequate for the specialized processing you require, you can provide your own implementations of these services. These implementations are then registered with the server using the extensibility interfaces.

The key characteristics of data cartridges areas follows:

• Data cartridges are server- based. Their constituents reside at the server or are accessed from the server. The bulk of processing for data cartridges occurs at the server, or is dispatched from the server in the form of an external procedure.

• Data cartridges extend the server. They define new types and behavior to provide componentized, solution-oriented capabilities previously unavailable in the server. Users of data cartridges can freely use the new types in their application to get the new behavior. Having loaded an Image data cartridge, the user can define a table Person with a column Photo of type Image.

• Data cartridges are integrated with the server. The extensions made to the server by defining new types are integrated with the server engine so that the optimizer, query parser, indexer and other server mechanisms recognize and respond to the extensions. The Oracle8i Extensibility Framework defines a set of interfaces that enable data cartridges to integrate with the components of the server engine. For example, the interface to the indexing engine allows for domain-specific indexing. Optimizer interfaces similarly allow data cartridges to specify the cost of accessing data by means of its functionality.

• Data cartridges are packaged. A data cartridges is installed as an unit. Once installed, the data cartridge handles all access issues arising out of the possibility that its target users might be in different schema, have different privileges and so on.