In this paper, we will focus on tutoring design in the context of online learning activities. Our problem concerns the computer support used by a designer to describe tutoring, as regards the specification of the tutors' roles and actions or the support tools for their activity. After presenting the limits of educational modeling languages in terms of tutoring, we will propose an organizational model of tutoring called TRITON. We will show its interest and its easy integration in EMLs through two case studies: IMS-LD and LDL, for which we propose an extension to enrich the tutoring scenario.