XML pipeline
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In computer science, an XML Pipeline is formed when XML (Extensible Markup Language) processes, sometimes called XML transformations, are connected together.
For instance, given a two transformations T1 and T2, the two can be connected together so that an input XML document is transformed by T1 and then the output of T1 is fed as input document to T2. Simple pipeline like this one are called linear, as a single input document always goes through the same sequence of transformation to produce a single output document. Non-linear pipelines can include:
- Conditionals — where a given transformation is executed if a condition is met while another transformation is executed otherwise
- Loops — where a transformation is executed on each node of a node set selected from a document or a transformation is executed until a condition evaluates to false
- Tees — where a document is fed to multiple transformations potentially happening in parallel
- Aggregations — where multiple documents are aggregated into a single document
- Exception Handling — where failures in processing can result an alternate pipeline being processed
Pipeline languages
XML Pipeline languages are used to define pipelines. The definition can understood by a pipeline engine that given a pipeline definition can create the processes, connect them together and execute the pipeline. Existing pipeline languages include:
- W3C XML Pipeline Definition Language is specified in a W3C Note and Sun provides an implementation.
- Cocoon sitemap allows the declaration of linear pipelines
- XPL is the OXF XML Pipeline Language. It allows the declaration of complex pipelines with conditionals, tees and aggregations.
External links
- W3C XML Pipeline Definition Language (http://www.w3.org/TR/xml-pipeline/Overview.html)
- Sun's XML Pipeline Definition Language Controller Implementation (http://wwws.sun.com/software/xml/developers/pipeline/) [Link broken, 22 Dec 04]
- Cocoon sitemap (http://cocoon.apache.org/2.0/userdocs/concepts/sitemap.html)
- XPL (http://www.orbeon.com/ois/doc/reference-xpl-pipelines)