Article:		Enterprise Application Integration using Apache Cocoon 2.1
Subject:		Conditionals
Date:		2003-11-21 15:40:31
From:		Erik Bruchez
This is not a bad article at all, but I thought I would comment on one point. "Pipeline lock-in", as the author says, is just a way of saying that Cocoon pipelines do not support conditionals, i.e. they do not allow you to take a different branch of execution based on the results of a previous step in the pipeline. If this is "by design", as I have read and heard a few times by now, it is a design that is hard to defend. The author's argument that Cocoon is SAX-based does not hold water either: consider that some components in a Cocoon pipeline do not support pure streaming, starting with XSLT. Xalan can be put in a mode where it starts outputing SAX events before reading its input is completed, but typically will not happen: in many cases, an XSLT transformation needs to have read the entire input document before being able to generate most of its output. The bottom line is that using conditionals in a SAX pipeline may impact streaming in different ways, yes, but so does using XSLT! This is how you would implement a condition in XPL, the OXF (http://www.orbeon.com/oxf/) pipeline language: <p:config xmlns:p="http://www.orbeon.com/oxf/pipeline"> <!-- First transformation --> <p:processor uri="oxf/processor/xslt"> <p:input name="data" href="foo.xml"/> <p:input name="config" href="foo.xsl"/> <p:output name="data" id="result"/> </p:processor> <p:choose href="#result"> <p:when test="/error"><!-- This is an XPath expression --> <!-- Execute part of pipeline when there was an error --> ... </p:when> <p:otherwise> <!-- Execute part of pipeline when there was no error --> ... </p:otherwise> </p:choose> </p:config> The problems the author encountered with the limitations of Cocoon pipelines are I think one of the major reasons so many people have been (and will be for a long time) frustrated with Cocoon. -Erik

Previous Message

Next Message