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Build applications with less code: MetaBOX and the declarative programming model.

Article Excerpt
This article shows how to build database Web applications using Oracle, two open-source frameworks, and MetaBOX software. Building database Web applications is commonly a repetitive task; many such applications are based on insert/delete/update statements of tables in a form of simple rows, multiple rows, or master/detail combinations.

To make this kind of application, many products offer different solutions--we can divide them into procedural or declarative approaches. These products provide wizards or code generators to help developers in the developing stage.

Depending on which technologies these generators use--pure HTML or XML--developers need to work more or less to get the desired output and maintain their applications. The procedural approach requires developers to know what they need and how to obtain it. Code generators for this approach generally use some kind of metadata from the applications such as tables, views, primary keys, foreign keys, and so on, and generate templates of the code for the application. An example of this approach is JSP generator of Oracle9i JDeveloper.

Developers who work with the declarative approach handle more abstract concepts such as table usage, permissions on these tables, primary keys, foreign keys, LOVs, and so on.

Both approaches have benefits and drawbacks. For example, the declarative approach has good productivity, portability, quality, and performance behaviors, but it's less flexible, and the performance improvement is for a certain application's domain.

On the other hand, the procedural approach is good for performance and flexibility, but the environment is less productive and less portable, and the quality of the code depends on the developer's skill. This article will explore a product developed on top of two open-source projects, named MetaBOX, that provides declarative development for Oracle Web applications. It uses XML as the key technology to decouple presentation from content, because many of a Web application's changes involve presentation concerns.

MetaBOX uses the DBPrism Servlet Engine framework as a connector for the Apache Cocoon framework and generates the application's XML code inside an Oracle database running a stored procedure. This means that you use the database engine not only to execute SQL statements, but also to directly return a complex XML representation of the application data stored inside as well.

What Is DBPrism?

DBPrism is an open-source framework based on servlet technology to generate XML from a database. It began as servlet replacement for the Oracle Web Server PL/SQL Cartridge; then it was extended to generate XML into the database side, transforming it in an active database.

Other technologies, such as Apache XSP or Oracle XSQL Servlet, generate XML into the Web server side and use the database only to return SQL. They can use stored procedures, but 99% of these applications put the logic into the Web server side.

How does it work?

DBPrism is a middleware component that interprets a request from different sources and executes a database stored procedure using the information coded into the request.

DBPrism automatically transforms, for example, a standard HTTP request into a stored procedure call using the arguments extracted from the URL. After this execution DBPrism collects the generated XML, or HTML, and returns it to the requester.

Working as stand-alone servlet, DBPrism is fully compatible with the Oracle mod_plsql component, providing seamless integration with applications developed with Oracle WebDB or Oracle Designer...

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