Managing the Systems Development Life Cycle:Conceptualization of Alternative Designs.

Conceptualization of Alternative Designs

The purpose of the conceptualization phase is to produce several alternative conceptual solutions that satisfy the system requirements identified during systems analysis. By presenting users with a number of plausible alternatives, the project team avoids imposing preconceived constraints onto the new system. These alternative designs then go to the systems selection stage, where their respective costs and benefits are compared and a single optimum design is chosen for construction.

HOW MUCH DESIGN DETAIL IS NEEDED?

The conceptual design phase should highlight the differences between critical features of competing systems rather than their similarities. Therefore, system designs at this point should be general. The designs should identify all the inputs, outputs, processes, and special features necessary to distinguish one alterna- tive from another. In some cases, this may be accomplished at the context diagram level. In situations in which the important distinctions between systems are subtle, designs may need to be represented by lower-level data flow diagrams (DFDs) and even with structure diagrams. However, detailed DFDs and structure diagrams are more commonly used at the detailed design phase of the SDLC. We shall discuss the transition from detailed DFD to structure diagram in Chapter 14.

Figure 13-6 presents two alternative conceptual designs for a purchasing system. These designs lack the details needed to implement the system. For instance, they do not include such necessary components as:

• Database record structures.

• Processing details.

• Specific control techniques.

• Formats for input screens and source documents.

• Output report formats.

The designs do, however, possess sufficient detail to demonstrate how the two systems are conceptually different in their functions. To illustrate, let’s examine the general features of each system.

Option A is a traditional batch purchasing system. The initial input for the process is the purchase requisition from inventory control. When inventories reach their predetermined reorder points, new inventories are ordered according to their economic order quantity. Transmittal of purchase orders to suppliers takes place once a day via the U.S. mail.

In contrast, Option B employs electronic data interchange (EDI) technology. The trigger to this system is a purchase requisition from production planning. The purchases system determines the quantity and the vendor and then transmits the order online via EDI software to the vendor.

Both alternatives have pros and cons. A benefit of Option A is its simplicity of design, ease of implementation, and lower demand for systems resources than Option B. A negative aspect of Option A is that it requires the firm to carry inventories. On the other hand, Option B may allow the firm to reduce or even eliminate inventories. This benefit comes at the cost of more expensive and sophisticated system re- sources. It is premature, at this point, to attempt to evaluate the relative merits of these alternatives. This is done formally in the next phase of the SDLC. At this point, system designers are concerned only with identifying plausible alternative designs.