1. A method of executing a workflow in a computer, comprising: representing a main workflow of at least one computer as a series of steps which are linked to define the workflow, the steps being grouped in at least two groups; representing a transition workflow as at least one transition step, the transition step not being linked to the steps of the main workflow; defining a rule for executing the transition workflow based on transitions between steps of different groups; executing in at least one computer the steps of the main workflow in an order defined by the links; evaluating the rule to determine whether the rule applies when, during the executing, a step from one of the groups is followed by a step from another of the groups; and executing in at least one computer the steps of the transition workflow when the rule applies.