Designing the Graphical User Interface › User Interface Design

User Interface Design

One of the fundamental principles of GUI is that the design must be closely mapped to the user's needs. To accomplish this, it is essential to have a thorough understanding of the users' needs. You must also understand who the users are and how they will use the interface. This understanding must form the basis of the windows you design.

Traditional block mode interfaces reflect an expectation that tasks are linear in nature. In a linear program, a well-defined series of steps should lead to a single definable goal. For example, consider the role of a data entry operator assigned to type data as quickly and accurately as possible. Such a task is repetitive and linear in nature, which makes it better served by a simple block mode, form-driven interface.

Many tasks are not repetitive or linear. Consider a more open-ended task such as word processing a document. This task may involve accessing several sources of information, such as other word-processed documents for text, a spreadsheet for a data, and a graphics package for a diagram. The performance of the task involves the ability to make decisions and, as a result, requires an open task structure.

An open task structure is also needed when the data entry operator's work may be interrupted by some external business event. The operator may need to suspend the task while switching to a higher priority assignment.

The linear versus open-task models are summarized in the following illustration.

The linear task structure is task-oriented. Block mode interfaces tend to be task-oriented.

The open-task structure is user-oriented. Properly designed GUIs tend to be user-oriented.

You should be aware of this major distinction as you move into the world of GUI design if you normally build block mode interfaces.

A GUI allows a closer mapping to the user task structure in the following ways:

• Interleaving—A user often starts a task, only to be interrupted with one of higher priority. The user suspends the first assignment while performing the high priority task. The user returns to the first task at the point of interruption after completing the high priority task.
• Single task, multiple application—The user employs several applications to complete one task. This task is usually of a managerial nature. For example, scheduling a meeting may require the use of a diary, electronic mail on the server. The user may also refer to the minutes of the previous meeting held as a word processed document on the client.
• Single application, multiple tasks—The user uses one application to complete several tasks. For example, employees use the electronic mail system for social interaction, cascading company notices to subordinate staff, and taking part in ad hoc discussions.
• Multiple representations—A variety of visual representations are used on the same underlying data. For example, numbers may be viewed one at a time, together in a table, or as a chart or graphic.
• Multiple sources—The user requires access to several sources of information or processes (typically on different machines) to complete the task.
• Reminding and feedback—The user may become disoriented in the computing environment, so information on what tasks are currently active (a you are here function) becomes essential.
• Context signaling and re-orienting—The users may require a reminder of what they were doing in a particular task. For example, on resuming a task the user is informed of the last command executed in the window before the task was suspended.