A collection of network-resident software services accessible via standardized protocols, whose functionality can be automatically discovered and integrated into applications or composed to form more complex services. (Hull et al. 2003)
Hull, R., M. Benedikt, V. Christiphides, J. Su. 2003. "E-Services: A Look Behind the Curtain." Proceedings of Symposium on Principles of Database Systems, 9-12 June, 2003, San Diego, CA.