Construct a class diagram for the following information system provided in a text editor: The information system in the text editor provides a simple hypertext reading facility enabling on-line documentation to be browsed from within the editor. The information system consists of a number of files, each roughly corresponds to a single document. Each file is divided into a number of nodes, each node containing a small amount of text describing a particular topic. One node in the system is identified as the directory node: it contains information about the files available in the information system, and is presented to the user when the system is started. Nodes are connected together by links: each link connects two nodes, and operations are provided enabling the user to move from one node to another via a link. In this way, it is possible to browse through the complete document. There are three important kinds of links, called up, next and previous links. The names imply that the nodes in a document will be structured in a hierarchical manner, but this is not enforced by the system. In addition to links, a node can contain a menu. A menu consists of a number of entries, each of which connects to another node in the system. When the system is running, a record is kept in a history list of all the nodes that have been visited, thus enabling users to retrace their path through the document