The document discusses formalizing message exchange patterns (MEPs) using BPELlight. It describes limitations of WSDL 1.1 and 2.0 in supporting complex MEPs beyond request-response. BPELlight extends BPEL to define MEPs independently of WSDL. Complex MEPs defined in BPELlight can then be referenced from WSDL 2.0 operations. This allows formal description of MEPs and improved modeling of message-based web services interactions.