A first electronic device maintains a directed acyclic graph to represent content collaboratively edited by the first device and one or more second devices of multiple collaborating devices. The first device receives one or more editing inputs from one or more devices of the multiple collaborating devices. The first device modifies the directed acyclic graph based on relationships between the editing inputs and existing content objects embodied in the directed acyclic graph, traverses the directed acyclic graph in accordance with a predetermined ordering rule to obtain an object sequence, and, if a first editing input of the one or more editing inputs modifies a first existing sketch content object represented in the directed acyclic graph, updates a command sequence associated with the first existing sketch content object by merging each individual drawing command included the first editing input with a command sequence associated with the first existing sketch content object.