A method of generating a sequence of commands to gather information using a directed tree graph includes providing a plurality of goals, each goal having a weighting, and a set of commands that lead to completion of the goals. A directed tree graph is constructed comprising a root node, respective leaf nodes associated with the goals, and one or more parent nodes. Each node is associated with one command, the command having the potential to complete any goals associated with the node and all the goals associated with any subordinate nodes. The priority of each command is determined, based on the sum of the goal weightings of leaf nodes subordinate to the node associated with the command. One or more commands is executed, a command having a higher priority being executed before a command having a lower priority.