Learning objects are considered as complex signs, since they convey meaning through a physical support and are related to real or conceptual object. In addition, it is possible to define a sequence of learning objects that can be modeled as having a narrative structure the advantage of this proposal is that, from the structural theory of narrative, content and expression can be treated separately so that a composition model can be devised independently of the specific media employed to express them. Learning objects are expressed by means of heterogeneous media types that have spatial, temporal and semiotic aspects. These attributes impose space, time and semiotic constraints on this sequence that can influence pedagogical aspects producing a cognitive overload because different media types engage different perceptional channels (e.g. visual, auditive) and determine the way information is processed. The discussion on these features of learning objects composition is illustrated by some examples stressing the benefits of the proposed approach.