Recent works about the activity-oriented approach et educational modeling languages ask questions about the pedagogical scenario concept. The aim of this paper is to define the foundations of a new engineering approach based on scenarios. We propose a conceptual framework, a precise vocabulary and a taxonomy of scenarios, and we focus on relationships between activities and resources. We also give some answers to questions linked with such approaches, particularly concerning the resource aggregation paradigm and new reusing strategies. KEYWORDS Standards and interoperability, Learning scenario, Educational Modeling languages, IMS Learning Design, LOM