1. A computer-readable storage medium storing therein a computer program that causes a computer to perform a procedure comprising: identifying, among tasks included in a plurality of workflows individually including one or more tasks using a resource, a plurality of tasks using the resource based on workflow definition information that defines content of each of the tasks included in the plurality of workflows; determining an execution sequence of the identified tasks based on the content of each of the identified tasks, defined in the workflow definition information; and identifying, among the identified tasks, one or more tasks whose execution is omissible based on the content of each of the identified tasks and the execution sequence.