End users of on-line applications consider the user interface to be the most important aspect of the system. This interface makes the user feel comfortable when using an online transaction. If it does not succeed in this respect, it is unlikely that the user will feel that the transaction serves its purpose.

The design of the user interface is the responsibility of the analyst assigned to the development of the on-line system. The design group should work with the end users to determine their requirements and level of expertise. After the design process has begun, the user group should remain involved in the overall development to ensure that the end result meets their needs.

The analyst should keep in mind that most users are not data processing specialists. A programmer or analyst should not fall into the common trap of creating an interface that merely makes his job easier. Simplifying the process of designing and creating the application program often comes at the expense of the user's requirements.

Screen Design

The primary source of information in an on-line system is the terminal display. An effective screen display will make a transaction easy to use. Human factors must be considered when deciding how information is to be presented on the terminal screen. A common mistake in screen design is to display too much of information on a single screen. A display screen should not be crowded. To avoid this, it is sometimes necessary to use more than one screen to display data. Although this may complicate the programmer's job, the use of multiple screens can aid the user.

Information should be logically arranged so that important data is easy to locate. If a screen is used to enter data, the format of that data should be consistent with that of any input forms used during entry. Data fields should be accurately and clearly labeled to avoid confusion. In addition, terminal features such as field protection and highlighting can be used to enhance appearance and ease of use.


Another important consideration when designing the screens to implement a dialogue is the use of instructions. Instructions should be provided to direct the user through the processing of a transaction from beginning to end. As a function or step is completed, the user should be told what to do next. If there are several options available, the instructions should help the user to make the appropriate choice.

Instructions should be simple, but not cryptic. If any ambiguity is introduced by over simplifying the instructions, the designer runs the risk of confusing the user and increasing the possibility of error. If the skills of the users vary, it may be desirable to set up varying help levels for the display of instructions. More skilled users can then turn off detailed instructions, while no vice users can still benefit from those instructions.

Error Messages

Even when a user has been well trained in how to use a transaction and good instructions have been provided, errors do occur. These errors may be the result of mistakes in data entry or a system or program error. No matter what caused the error, the user must be kept informed of error conditions and given some guidance about what to do next.

Like instructions, error messages must be simple, yet precise. They should explain the error in terms the user will understand. Cryptic or coded error messages should be avoided. The use of acronyms and abbreviations" should be avoided in error messages because they may cause confusion.


The design of the user interface should be consistent for all transactions that make up an application system. As users become familiar with the format used to present the information at the terminal screen, they will become more skillful in using that information. Confusion may result if the screens in a system use different formats, instructions and error messages. On the other hand if standard methods are used to develop the user interface, users will not spend valuable time adjusting to format differences between transactions.

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