The e-learning represents the new frontier of education, significantly improving the learning process. We propose an e-learning model, providing both teachers and students with an open and modular learning environment. We then focus on courses personalization, both in terms of contents and teaching materials, according to each student's needs and capabilities, also taking teacher guidelines into account. To accomplish this, we model courses/lessons as graph nodes, where arcs represent their precedence/succession relationships. We outline a course generation/presentation engine which allows the creation of personalized learning paths (subgraph) by extracting lessons, eliminating those known to the student, and arranging them into a tree including all possible paths starting from the student's possessed knowledge towards desired knowledge.