Software Engineering-User Interface Design


The overall process for designing a user interface begins with the creation of different models of system function (as perceived from the outside). The human- and computer-oriented tasks that are required to achieve system function are then delineated; design issues that apply to all interface designs are considered; tools are used to prototype and ultimately implement the design model; and the result is evaluated for quality.

Interface Design Models

Four different models come into play when a user interface is to be designed. The software engineer creates a design model, a human engineer (or the software engineer) establishes a user model, the end-user develops a mental image that is often called the user's model or the system perception, and the implementers of the system create a system image . Unfortunately, each of these models may differ significantly. The role of interface designer is to reconcile these differences and derive a consistent representation of the interface.

A design model of the entire system incorporates data, architectural, interface, and procedural representations of the software. The requirements specification may establish certain constraints that help to define the user of the system, but the interface design is often only incidental to the design model. The user model establishes the profile of end-users of the system. To build an effective user interface, "all design should begin with an understanding of the intended users, including profiles of their age, sex, physical abilities, education, cultural or ethnic background, motivation, goals and personality". In addition, users can be categorized as

• Novices. No syntactic knowledge of the system and little semantic knowledge of the application or computer usage in general.

• Knowledgeable, intermittent users. Reasonable semantic knowledge of the application but relatively low recall of syntactic information necessary to use the interface.

• Knowledgeable, frequent users. Good semantic and syntactic knowledge that often leads to the "power-user syndrome"; that is, individuals who look for shortcuts and abbreviated modes of interaction.

The system perception (user's model) is the image of the system that end-users carry in their heads. For example, if the user of a particular word processor were asked to describe its operation, the system perception would guide the response. The accuracy of the description will depend upon the user's profile (e.g., novices would provide a sketchy response at best) and overall familiarity with software in the application domain. A user who understands word processors fully but has worked with the specific word processor only once might actually be able to provide a more complete description of its function than the novice who has spent weeks trying to learn the system.

The system image combines the outward manifestation of the computer-based system (the look and feel of the interface), coupled with all supporting information (books, manuals, videotapes, help files) that describe system syntax and semantics. When the system image and the system perception are coincident, users generally feel comfortable with the software and use it effectively. To accomplish this "melding" of the models, the design model must have been developed to accommodate the information contained in the user model, and the system image must accurately reflect syntactic and semantic information about the interface.

The models described in this section are "abstractions of what the user is doing or thinks he is doing or what somebody else thinks he ought to be doing when he uses an interactive system" . In essence, these models enable the interface designer to satisfy a key element of the most important principle of user interface design: "Know the user, know the tasks."

The User Interface Design Process

The design process for user interfaces is iterative and can be represented using a spiral model  Referring to figure, the user interface design process encompasses four distinct framework activities :
1. User, task, and environment analysis and modeling
2. Interface design
3. Interface construction
4. Interface validation

The spiral shown in figure implies that each of these tasks will occur more than once, with each pass around the spiral representing additional elaboration of requirements and the resultant design. In most cases, the implementation activity involves prototyping—the only practical way to validate what has been designed.

The initial analysis activity focuses on the profile of the users who will interact with the system. Skill level, business understanding, and general receptiveness to the new system are recorded; and different user categories are defined. For each user category, requirements are elicited. In essence, the software engineer attempts to understand the system perception for each class of users.

Once general requirements have been defined, a more detailed task analysis is conducted. Those tasks that the user performs to accomplish the goals of the system are identified, described, and elaborated (over a number of iterative passes through the spiral). 
The analysis of the user environment focuses on the physical work environment.
Among the questions to be asked are
Where will the interface be located physically?
Will the user be sitting, standing, or performing other tasks unrelated to the interface?
Does the interface hardware accommodate space, light, or noise constraints?
Are there special human factors considerations driven by environmental factors?

The information gathered as part of the analysis activity is used to create an analysis model for the interface. Using this model as a basis, the design activity commences.

The goal of interface design is to define a set of interface objects and actions (and their screen representations) that enable a user to perform all defined tasks in a manner that meets every usability goal defined for the system.

The implementation activity normally begins with the creation of a prototype that enables usage scenarios to be evaluated. As the iterative design process continues, a user interface tool kit   may be used to complete the construction of the interface.

Validation focuses on (1) the ability of the interface to implement every user task correctly, to accommodate all task variations, and to achieve all general user requirements; (2) the degree to which the interface is easy to use and easy to learn; and (3) the users’ acceptance of the interface as a useful tool in their work.
Share this article :
 
Copyright © 2012. Best Online Tutorials | Source codes | Programming Languages - All Rights Reserved