Due to the complexity of distributed applications, understanding their behaviour is a challenging task. The top-down use of suitable abstraction hierarchies is frequently proposed to manage this complexity. One commonly used abstraction is to group primitive events into abstract events. This paper discusses some of the problems encountered when displaying executions at abstract levels and presents a graphical representation for convex abstract events. Using convex events as building block for abstract execution visualizations avoids the identified problems. The proposed representation can easily be included in the process-time diagrams frequently employed to depict the behaviour of distributed applications. Such visualizations, in turn, are helpful during the construction, debugging, and monitoring of distributed applications as well as in trying to understand old ``legacy'' code in a program-understanding task. We enhanced the visualization component of a prototype distributed debugger with the facility to depict executions at various abstraction levels. Examples of the resulting abstract visualization for the execution of a non-trivial distributed application are discussed. These abstract visualizations are essential to minimize the complexity of the understanding process, and support top-down debugging.

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