0.33.4: XML application model
XML applications can be deployed in a logical three-tier environment as follows:
- Tier 1
- XML-enabled user agents parse an XML document, apply stylesheets, and present
the document contents. Some user agents convert the XML document to HTML for
presentation. Microsoft Internet Explorer 5 is an example of an XML-enabled
user agent that can display XML documents without first converting them to
HTML. Although only a small number of XML-enabled user agents are available
today, their number is expected to grow as the popularity of XML increases.
- Tier 2
- XML-based servlets and applications provide server-side XML processing.
A Web server (an HTTP server) can be configured to serve static XML documents.
However, to process and dynamically generate XML documents, the Web server
base function must be extended. The XML Document Structure Services in the
Application Server provide such an extension of the Web server and
enables Tier 2 servlets (database connectors and integration applications)
to parse, generate, manipulate, and validate XML-based dynamic content.
This content is sent to Tier 1 and interchanged with other servlets.
Tier 2 can also be used to selectively apply stylesheets
to XML documents when the Tier 1 devices do not support
the application of XSL stylesheets to XML documents.
- Tier 3
- The content for dynamically generated XML documents can be retrieved from
data servers. Depending on the XML application, the extracted data can be
returned as an XML document or returned in JDBC or some other format to a servlet
that converts the data to an XML document.
In the future, XML-capable Java beans for accessing
databases should be commercially available.