Docland XML Engine

The Docland XML engine (DXe) is component technology for XML. DXe assembles XML documents from components of XML. DXe can be used to build complete documents such as XHTML web pages by assembling selected XML Components. A DXe enabled server can selectively assemble components into documents at run-time. DXe can also be used at design time to generate HTML files for traditional web servers.

DXe enables web developers to move beyond today's monolithic approach to web content generation and to utilise powerful component based techniques for building web pages and other XML documents.

With DXe, the presentation layer of a web application can be developed as a set of reusable XML components. These components can be assembled in a hierarchical fashion to generate the web pages for the application.

DXe is modelled on "multiple class inheritance" as used in some object oriented programming languages.

Features of DXe

Using DXe, a web page can be assembled from smaller components - each component encapsulating some characteristic of the page.

For example, an HTML form may contain both input fields and text labels. Using DXe, such a form can be developed from two components - one component containing the input fields and any layout information, and a second component containing the English language text for the labels. DXe can combine these to generate a complete form with English language labels. By replacing the English language component with one containing German language labels, a German form can be generated.

DXe is designed to generate pages at run time, so a single page can be presented in different ways depending on runtime conditions. For example, a menu on a web page could be presented in German or English depending on the language used by the browser.

DXe performs two core functions:

• DXe merges the content of XML components to create web pages
• DXe maintains the consistency of links and references in XML components

DXe complements and adds value to current presentation technologies such as JSP and XMLC, without impinging on the design of the business logic programs of a system.

Using DXe in J2EE

The Docland XML Engine is a Java servlet filter that process the output of Servlets and JSPs. DXe is also implemented as a servlet "wrapper" class for earlier versions of the Java Servlet API

Application developers can construct the presentation layer of their application using XML components.

Figure 1: DXe in a 3 tier application.

DXe parses the XML generated by a servlet or JSP and generates a web page by combining this dynamic content with other components. The other components can be local (on the same server) or remote (on other servers), and may contain static content read from files, or dynamic content - such as the results of database queries.

DXe's main features are:

• Web page assembly from reusable XML Components.
• Assembly of web pages from distributed sources
• Intelligent assembly of web pages based on runtime conditions.
• Maintains consistency of links in XML and XHTML components

Figure 2: DXe builds web pages from XML Components.

DXe implements a rules-based process for merging XML content. XML documents adhere to stricter rules of structure than HTML. This makes it simpler and faster to process XML content. DXe uses the innate structure of XML content to merge into web pages.

Benefits of DXe

• Improve consistency across sites and within applications.
• Reduce development and maintenance costs by reusing components.
• Reduce complexity in web pages by factoring complex pages into simpler components.
• Encapsulate strands of related content as separate components.
• Create flexible presentation layers for multi-tier applications.
• Deliver customised content via intelligent runtime assembly of pages.
• Simplify applications by assembling documents from distributed sources.
• Improve content development and maintenance processes.
• Reduce development effort and increase the value of developers time.
• Localise web content using local page assembly servers.
• Improve security and content management using component level access control.
• Support distributed development & maintenance.
• Use existing XML authoring tools to develop XML components.