ordered trees tree is ordered if there is meaningful linear order among the children of each nodethat iswe purposefully identify the children of node as being the firstsecondthirdand so on such an order is usually visualized by arranging siblings left to rightaccording to their order example the components of structured documentsuch as bookare hierarchically organized as tree whose internal nodes are partsand sectionsand whose leaves are paragraphstablesfiguresand so on (see figure the root of the tree corresponds to the book itself we couldin factconsider expanding the tree further to show paragraphs consisting of sentencessentences consisting of wordsand words consisting of characters such tree is an example of an ordered treebecause there is well-defined order among the children of each node book preface part ch ss ss part ch ch ss ss ss ss references ch ss ss figure an ordered tree associated with book let' look back at the other examples of trees that we have described thus farand consider whether the order of children is significant family tree that describes generational relationshipsas in figure is often modeled as an ordered treewith siblings ordered according to their birth in contrastan organizational chart for companyas in figure is typically considered an unordered tree likewisewhen using tree to describe an inheritance hierarchyas in figure there is no particular significance to the order among the subclasses of parent class finallywe consider the use of tree in modeling computer' file systemas in figure although an operating system often displays entries of directory in particular order ( alphabeticalchronological)such an order is not typically inherent to the file system' representation