Abstract: Web service composition has become an emerging and promising technology for designing and building complex applications out of single Wclrbased software components. Currently, there already arc several such systems based on different technology. Question along with these systems is which system should be chosen as a composition tool. This paper gave a function model of general Web service composition system,based on which analyzed twelve systems which already exist. According to the functions systems have, it divided these systems into different categories and gave an outlook to essential future research work.

Key words: Synthesized service, Component service, Service composition system, Execute engine