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4.5. USER INTERFACEOne of the most critical design issues when developing an expert system, a lesson first learned by the developers of MYCIN, is the importance of accommodating the user by offering an easy-to-use interface, equipped to handle all of the user's requirements. It is, therefore, important to learn of the user's needs and desires before choosing a shell. Some general points to consider are offered in the following paragraphs. Display type. The early expert systems all relied on a text-based display. Questions were posed to the user in text and answers were provided via keyboard typing or by selecting from a menu. Today, most shells provide a graphical-user-interface (GUI) that permits the user to interact through a point-and-click method. Since most computer users today are more accustomed to a GUI, and computer novices find the interaction more intuitive, a shell offering a GUI is usually preferable. Information entry. There is a wide range of methods by which the user can enter information into the system. It may be as simple as typing an answer to some question, or as extensive as filling out an entire form. A question might be posed requiring a single answer, or one that permits the user to select multiple answers from a list. Graphical input displays typically available are radio buttons, check boxes, forms, scroll bars, and pushbuttons. Some shells provide limited default ways for entering information, while others permit the designer to choose from a variety of methods while creating the display from scratch. Information display. The expert system must be able to display its findings to the user. This information might be the final conclusion, or intermediate findings discovered during the session. Typical ways of displaying information are message boxes, value boxes, radio buttons, check boxes, forms, and graphics. Interface control. The user must always feel in control of the session. This includes an easy way of starting and ending a session, and readily accessible ways of activating needed control during the session. Some shells offer default methods for managing these tasks, while others require the designer to develop the techniques. For a graphical interface, this control is typically done with pushbuttons or a menu-select scheme. A user may also request other special features, such as save-case and what-if. The save-case feature permits the user to save the context of the present session, either for reporting requirements or for later what-if system testing. The what-if feature allows the user to change an answer to some question from a completed session, in order to see what impact the new answer might have on the final results. 4.6. SYSTEM INTERFACEThe early shells were limited to creating stand-alone expert systems, with no capability of interacting with other programs. Today, most shells offer an open architecture that permits the developed system to share information with external software such as databases, spreadsheets, and procedural programs like C and Fortran. Being able to embed an expert system within an established software environment greatly enhances its applicability and improves its portability between applications. What software the expert system can interact with, and how this interaction is established, varies widely among the shells. The smaller shells usually have limited access abilities, often only to a certain database or a specific procedural program written in the same language used in the shell development. They may also require the designer to write the code to perform the interaction. The larger shells typically interact with far more programs, and in general, also make the task of establishing the interaction easier, often providing a library of functions to support the effort. 4.7. HARDWAREThe platform on which the expert system will be developed and, if different, where it will be run, is a major consideration when selecting a shell. Overall, the platforms can be divided into four general categories: personal computers, workstations, minicomputers, and mainframe computers. The majority of expert systems have been developed on a PC, as illustrated in Figure 4 (Durkin, 1993).
Some vendors offer shells that will run on only one of these platforms. You can expect to find that the smaller tools only run on a PC. The vendors of larger shells often provide versions that can run on different platforms, but charge more for versions that run on the larger ones. This not only provides versatility in selection and portability of the developed software, but also offers an advantage to a company looking to take a low-risk approach to the project. For instance, a cheaper version can be used to develop the expert system on a PC to assess the project's feasibility; then, following successful testing, the more expensive version can then be purchased and the developed system deployed on a larger platform.
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