A group of two or more processes performed in series on an XML document where the output of the first process becomes input to the second and so on. Based on the document's contents, which may have been altered in a previous pipeline step, there may be a choice of which subsequent step is taken, similar to the logic in a program. There are several XML pipeline languages, including Orbeon Forms, Cocoon, smallx XML Pipelines and XProc. See XML.