The author wrote about notification-based Web service systems. To properly address the topic, the author devoted a significant portion to Web service references, which are, conceptually, like network handles that refer to Web services. Service references are particularly important for notification systems, which usually require subscribers to register service references to receive notification messages. Given that it appears in one form or another in almost every distributed system, service references are nothing new. Nevertheless, no standardized service reference exists for Web services. Among other things, the WS-addressing specification, which entered the W3C standardization process, specifies a construct called an endpoint reference (EPR), which is much like a service reference. The author is a member of the WS-addressing working group (WG), and we've made good progress toward turning the specification into a standard. The author discusses a few issues in the WG regarding the features needed to turn the EPR into a flexible and useful Web service reference.