The specifications of high-level distributed systems are usually associated with workflow systems, which can be implicitly mapped to Petri nets for analysis. An occurrence graph (O-graph) is the state diagram of a Petri net, and used to analyze the net. In this paper, we present a technique that reduces the O-graph building time by modifying the current O-graph based on previous one, instead of constructing a new one when a modification is done during workflow editing. The modifications are discussed based on two groups of edit activities in Petri nets: (1) addition of a node, arc, or token and (2) deletion of a node, arc, or token. A modification activity in workflow editing can be transformed into one or more of the above editing activities for the corresponding Petri net implicitly. Thus, an O-graph can be built efficiently in an incremental way. So is its analysis for the editing of workflow specification.