Tree Structures
Selecting the Right Display for the Right Purpose | Design and Layout | Functions and Control Elements | Reducing Hierarchy Levels
Tree structures (short: trees) and lists are elements that can be used to model a large amount of data in easily readable form. They are particularly well-suited to representing hierarchical dependencies and give the user a clear overview of a large quantity of information.
Do Use
Lists and tree structures can therefore be extremely effective when they are used for the following areas, for example:
- Trees allow an excellent overview of different objects that are related to one another. This means many objects are displayed, but each individual object only has a small amount of information.
- Trees allow the modeling of graphical relationships between objects. Illustrations of this type can help promote orientation and comprehension of the relationships for users charged with performing a task.
- Trees represent a central access point for navigation between different objects. The user can avoid frequent screen changes and having to remember where specific information is located.
- Trees allow fast access with direct manipulation (via drag and drop) of objects within the structure. As a result, trees are particularly well-suited to activities that require users to re-sort or move objects.
Do not Use
To enable the above features, the trees and activity structure must "fit" one another. In some situations, the use of trees can cause more problems than it solves. For example, you should not use trees to:
- Model existing hierarchical menu and navigation structures in the system without prior revision. Simply copying nested area menus into a tree structure does not help the user.
- Display complex information in trees, as well as interface elements like pushbuttons or checkboxes. This is not recommended due to the complexity of the resulting tree and the limited space available.
Problems
In addition, the use of trees results in other typical problems:
- Space requirements: The tree occupies space on the screen, restricting the size of the work area.
- Visual complexity: Because the overall screen is divided into different areas, it appears to be more complex.
- Complex interaction between index area and work area: Changes in views and highlighting for object selections have to be carefully coordinated between the two areas.
- Too much information: Displaying too much information for individual objects in a tree can quickly make the entire structure confusing.
- Misuse of icons and colors: It is easy to use unsuitable, too many, or confusing icons. The same thing applies to colors.
- Assigning functions: It is often unclear which pushbuttons affect the tree structure and which ones affect the data.
- Tree functions in menus: Functions that only apply to a specific tree structure can be "hidden" in various places in the menus.
