With the widespread use of full-text information retrieval, passage-retrieval techniques are becoming increasingly popular. Larger texts can then be replaced by important text excerpts, thereby simplifying the retrieval taskand improvingretrievale ectiveness. Passagelevel evidence about the use of words in local contexts is also useful for resolving language ambiguities and improving retrieval output. Two main text decomposition strategies are introduced in this study, including a chronological decomposition into text segments, and semantic decompositioninto text themes. The interaction between text segments and text themes is then used to characterize text structure, and to formulatespeci cationsfor informationretrieval, text traversal, and text summarization.