a page should be considered as a logical unit of data within the database and the frame a physical unit. unfortunately the terms node, page and frame are often used synonymously which may lead to some confusion. to the user of course a node is the same as a page and they are both identified by a 'page' number. to access a particular item of information, a simple progression down through the nodes to the page is all that is required, and then the frames of that page can be stepped through. this is facilitated by each node displaying up to ten choices, one of which may be taken by the user responding with the appropriate digit from 0 to 9. this simple method of access may be thought of as a question and answer session: the computer displays a question 'which of the ten choices do you want to make?’ and the user replies with the appropriate digit. a choice of 9 at node 17 moves the user to page 179. the flexibility of this logical access method is increased firstly by allowing cross-referencing from one branch of the tree to another and secondly by providing a few simple commands available to the user for accessing certain pages directly.