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50 The XML Files: Development of XML/XSL Applications Using WebSphere Studio
The latest version is Cocoon 2 and is available for download from:
http://www. xml.apache.org/cocoon/
It is a Web based application and must be run upon a Java Servlet 2.2 compliant
engine, and also Jakarta Tomcat 4.0.1
In Cocoon, everything can be perceived as part of a pipeline. A pipeline consists
of an input, some processing steps and then an output. Cocoon 2 makes use of
the SAX events between each processing step. Parts of the pipeline include a
generator and a serializer. The generator is used for input, the serializer
produces output and the transformer is used for processing intermediate steps.
These components can be grouped together into several distinct types,
depending on the roles they play within a pipeline:
Generators and reader: pipeline inputs
Generators are used for inputing data source and passing it on as a series of
SAX events. The simplest generator is therefore a SAX parser. Generally, any
data source that can be mapped to a series of SAX events can become the basis
for a generator.
Transformers and actions: processing steps
The main processing steps in the pipeline are handled by the transformers
(Figure 2-3). They accept SAX events as input, perform a number of useful
processing steps, and then the results produced are passed down the pipeline as
SAX events. The most common transformer one can find is the XSLT
Transformer. Input is fed into an XSLT processor which performs an XSLT
transformation. The results of the transform are then fed back into the pipeline as
SAX events.
Serializer: pipeline outputs
Serializers render the output from a stream of SAX events produced from a
generator or a transformer. The format of the output is dependent on the
serializer specified.
Serializers are the endpoints in Cocoon pipelines. The most
basic serializer is the XML serializer, which simply turns the SAX events back
into an XML document, while other serializer produce HTML, PDF documents,
and images to name a few. The serializers need to have the SAX events stream
to be of a particular XML vocabulary: A HTML Serializer turns XHTML into valid
HTML, a PNG images and PDF Serializer: Turns XSL-FO into a PDF document
and a SVG Serializer turns SVG into JPEG.