An important problem in analyzing distributed computations is the amount of information. In event-based models, even for simple applications, the n umber of events is large and t he c a usal structure is complex. Event a bstraction can be used to r e d uce the a p parent complexity o f a distributed computation.This paper discusses one important aspect of event a bstraction: causality among a bstract events. Following Lamport 24 , two c a usality relations are de ned on abstract events, called weak and strong precedence. A general theoretical framework based on logical vector time is developed in which s e v eral meaningful timestamps for abstract events are derived. These timestamps can be used to e ciently determine c a usal relationships between arbitrary abstract events. The class of convex abstract events i s i d enti ed as a subclass of abstract events t hat i s general enough to be widely applicable and restricted enough to simplify timestamping s c hemes used for characterizing w eak precedence. We explain why s u ch a simpli cation seems not possible for strong precedence.