— We discuss a learning model that enables the creation of optimal learning strategies that suit learners’ needs. A customized learning content is delivered to learners as managed sequences of learning activities which form a hierarchical structure that can be modeled by means of Petri Nets. Learning content customization is a dynamic process supported by a set of standards-based data models. The approach we adopted is implemented as Web services in a service-based learning architecture. Learning objects are sequenced according to learners’ responses to exercises and questions.