Properties of membership services

A membership service is used in a distributed system to maintain information about which sites are functioning and which have failed at any given time. Such services have proven to be fundamental for constructing distributed applications, with many example services and algorithms deened in the literature. Despite these eeorts, however, little has been done on examining the abstract properties important to membership independent of a given service. Here, these properties are identiied and characterized. Message ordering graphs are used to specify the eeect of each property on the message ow as seen by the application , and dependency graphs are used to characterize the relationship between properties. These graphs help diierentiate existing services, as well as facilitate the design of new services in which only those properties actually required by an application are included.