SPECIAL TOPICS IN REA MODELING
SUGGESTED ANSWERS TO DISCUSSION QUESTIONS
19.1Often it takes several sales calls to obtain the first order from a new customer. Why then does Figure 19-1 depict the relationship between the Call on Customer and Take Customer Order events as being 1:1?
When a sales person visits a customer it is represented by the event Call on Customer. Although single sales call may be followed by many orders from a customer over time, it is easier and more effective to evaluate sales force productivity by linking each sales call only to orders placed at the time of the sales call, that is, only those sales calls that linked to an order are successful. Hence, the maximum cardinality between the Call on Customer and the Take Order event is 1. However, a sales call does not always result in a sales order. Thus, the minimum cardinality from the Call on Customer event to the Take Order event is 0. Some orders, however, do not follow directly from a sales call. Therefore, the minimum cardinality from the Take Order event to the Call on Customer event is also 0.
19.2How could an automobile dealer model the use of loaner cars, which it gives to customers for free whenever they drop off a vehicle for maintenance that will take longer than one day to complete?
The loaner car arrangement could be handled the same as rental car arrangement, except that cash receipts will not be involved. The resource is the loaner car, the events are the loan (or free rental) of the car and its subsequent return, and the agents would be the customer whose car is in the service department and the employee who makes the loan arrangement.
19.3In what situations would you expect to model a relationship between an agent and a resource?
Relationships between agents and resources can be modeled for two reasons. Relationships between resources and suppliers provide information about preferred and alternate suppliers. Relationships between resources and employees can represent custody responsibilities. This would most likely be limited to high-cost and high-value resources.
19.4Why is depreciation not represented as an event in the REA data model?
Depreciation is not modeled as an event in the REA diagram because it is an accounting concept that arbitrarily allocates the cost of an acquired resource to different fiscal periods. Periodic depreciation is simply a calculation based on a formula (depreciation method) and a set of assumptions (estimated useful life, salvage value, etc.). Information about the formula and assumptions is stored in the resource entity for use in calculating periodic depreciation charges, but the calculation process itself is not an event, just as the processes of calculating the total amount of a particular sales transaction or the amount of an employee’s paycheck are not modeled as events.
19.5How would you model the acquisition of a digital asset, such as the purchase of software online (the software is downloaded and then installed on the purchaser’s computer)?
There is very little difference in modeling an event where a physical resource is sold as opposed to a digital resource. The digital asset must still be ordered, received, recorded, and paid for. The primary difference is that with digital assets, all of these functions occur almost simultaneously. Nonetheless, all aspects of acquiring digital assets must still be addressed just like a physical asset. Therefore, if the digital asset was purchased for resale, its acquisition would be recorded as a Receive Inventory event and another row in the inventory table would be created to represent this new product. If the software was purchased for use in the business, its acquisition would be recorded as a Receive Software event and another row in a Software resource table would be created.
19.6How are the similarities and differences between the purchase of services, such as telephone service, and the...