In order to structure multimedia learning material a data model is presented that specially addresses scalability and provides an high level of flexibility for interactive distance education environments. The model organizes learning objects in a set of nodes connected to each other through directed edges. Relationships capture didactic aspects and edges allow ordered sequencing of objects. The data organization is searchable, hierarchically structured and navigable according to paths that express the pedagogical strategy of the teacher. Model is mapped in an XML schema that is generic enough to be reused in different contexts and has been usefully applied in a C programming course.