In various industrial fields, the operators use pre-designed procedures either to solve problems or for troubleshooting. In the Parisian subway, such procedures exist since 1900. However, these procedures are not always exactly suited to the case at hand, and the operators generally prefer to customize a solution than to rely on fixed procedures. A new generation of decision support systems, so-called “intelligent” assistant systems, offers more flexible possibilities of cooperation between the users and the system. SART is such a system, for its design, we have modeled operators’ activity to model the cooperation between the operators and the system. As a result, we introduce the contextual graph paradigm, which appears as a possible computer representation of schemes that are used in psychology to describe human activities.