A computer supports generating a model of transactions in which services are processed in multiple layers. The computer refers to start times and end times of processings, which are invoked and generated from another processing in the services, of the same server to calculate time intervals between the processings. The computer generates possible thresholds indicating thresholds that are possible criteria for grouping the processings according to the time intervals between the processings. The computer puts together, for each of the generated possible thresholds, consecutive processings, in which the time intervals between the processings are equal to or smaller than the possible threshold, into the same group to generate a group that the processings belong to. The computer divides a group, among the generated groups, without a processing serving as an invoker into processing-by-processing groups. The computer determines the possible threshold with the least number of groups as the threshold.