Books are organized so that a story can be told or understood. This means that parts, chapters, subsections and sections of a book are normally related in terms of theme, time, and purpose. In that way a reader can understand the beginning, middle, and end of things in a logical way. Likewise, these parts of a book are organized so that the material in each section, chapter, etc. are related in terms of feelings, the time in the lives of characters that are discussed (for example, childhood, teen years, etc.), or some other way to categorize things so they relate or link to each other in some way. Likewise, clustering works by putting things in a type of order so that they are related by category, such as by geographic region or time, for example. To equate this to the way books are divided, clustering would be in the hierarchical and/or partitioning methods.