Ch. 9
Building Model-Driven Decision Support Systems

Spreadsheets are a very popular end-user modeling tool. A spreadsheet is based on the structure of an accounting spreadsheet that is basically a column-and-row pad. The intersections of the columns and rows are called cells. The user places numeric data or text in these cells. Then, the user writes formulas using functions to manipulate the data. Spreadsheets have many advantages over a paper accounting worksheet. Most notable is the modeling capability; users can write their own models and also conduct "What-If" analysis, scenario analyses and goal seeking. A scenario is a statement of assumptions about the operating environment of a particular system at a given time. In DSS, a scenario refers to conducting analyses with alternative assumptions about a financial model.

In spreadsheets, reports can be consolidated and data can be organized or sorted in alphabetical or numerical order. Other capabilities include setting up windows for viewing several parts of a spreadsheet simultaneously, and executing mathematical manipulations. These capabilities enable the spreadsheet to become an important tool for analysis, planning, and modeling. In addition to the ability of writing models with a spreadsheet, the software usually includes large numbers of built-in statistical, mathematical, and financial functions.

A major capability of spreadsheet programs is that numbers can be changed and the implications of these changes can immediately be observed and analyzed. A spreadsheet can be used to build static of dynamic models. A static model does not include time as a variable. For example, spreadsheets are used to build balance sheets. A dynamic model, on the other hand, represents behavior over time. For example, the balance sheet for a given year can be shown together with those of the five previous years.

Spreadsheets are used in almost every kind of organization in all functional areas. Some of these applications are not strictly DSS; they are more in the nature of the traditional MIS. The point is that with a spreadsheet, users do not have to wait a long time for the IS department to build an application. Managers can build applications on their own or with help from an Information Center very quickly and inexpensively.

End-user developed Model-Driven DSS will frequently have errors. All of the problems with this type of development that were discussed in Chapter 4 need to be addressed. One way to reduce errors and improve the usefulness of a Model-Driven DSS developed in a spreadsheet is to have an MIS staff member evaluate the application based on the following criteria:

• Accuracy. Are the results and calculations correct?
• Flexibility. Is it easy to change assumptions, parameters, and values? Is the application well documented?
• Understandability. Is it easy to understand the purpose of the Model-Driven DSS and how it is implemented in the spreadsheet?
• Auditability. Is it easy to audit the application? Is the organization of the workbook easy to understand? Can dependencies be traced in the application?
• Aesthetics. Are the spreadsheet screens attractive and well designed? Are any printouts easy to read?