Our analysis of prosodic patterns in spontaneous speech in French is based on the hypothesis that intonation, far from being the reflection of syntactical and rhythmical organisation only, also depends on informative structure. This hypothesis is illustrated here by the role of prosodic markedness in the expression of topic. We propose a bottom-up modelisation of prosody, from signal processing (segmentation and labelling of prosodic units according to perceptual constraints) to phonological representation in terms of autonomous principles which reflect the intonational structure as it is co-constructed by speaker and hearer. A functional reading of our prosodic model is then proposed, regarding constraints derived from informative structure for topic construction.