This work deals with the design of Loose Inter-Organizational Workflow (IOW). Loose IOW refers to occasional cooperation, free of structural constraints, where the partners involved and their number are not pre defined. We show that the design of Loose IOW application is very complex due to three factors: (i) the heterogeneity and distribution of the component processes, the organizations and the information (ii) the autonomy of each partner, which must be preserved (iii) the need to integrate in a coherent framework the three dimensions of a workflow: process, information and organization. One possible way to deal with this complexity, and to ease loose IOW applications design, is to use a well known software engineering principle: the separation of aspects, which aims at decomposing a system in communicating sub systems, each one coping with a relevant abstraction that requires a model to be structured and described. Following this practice, a loose IOW application must be though as three communicating models: an informational model, an organizational model and a process model. The first two models are represented with UML class's diagram, while the last model is described with Petri Nets with Objects (PNO), which are a formal language, have a very adequate expressive power and make the glue between the three workflow dimensions. We illustrate our solution through the well-known "reviewing papers" case study.