This case study leads to several important obser-vations: Frontiers can be identified when there are few bursts across a position and many before/after that position; words that are bursty at one level in the topic hierarchy (i.e., specific at this level) can become general for lower levels in the hierarchy; when going to lower levels in the topic hierarchy, the number of bursts decreases; there are segments with no bursty words.
burst analysis is relevant in the context of hierarchical topic segmentation, but an appropriate way to exploit it has to be proposed; we address this open issue in the following section.