The start of it all: Henry S. Thompson's Infoset Pipeline talk
Sean McGrath's keynote from XML Open 2004 Performing impossible feats of XML processing with pipelining
The W3C XML Processing Model Workshop of 2001
The Sun/Markup/... XML Pipeline submission to W3C
Markup Technology's re-interpretation of the Sun proposal
Sean McGrath's XPipe
Norm Walsh's SXPipe
The Orbeon XPL submission to the W3C
1060 Research's NetKernel
The W3C XML Processing Model Working Group
The first public Working Draft of XProc: An XML Pipeline Language