Data Modeling

CHAPTER 17 DATA MODELING AND DATABASE DESIGN SUGGESTED ANSWERS TO DISCUSSION QUESTIONS 17.1 Why is it not necessary to model activities such as entering information about customers or suppliers, mailing invoices to customers, and recording invoices received from suppliers as events in an REA diagram? The REA data model is used to develop databases that can meet both transaction processing and management analysis needs. Only events that either (1) directly change the quantities of resources, (2) represent commitments to future exchange events, or (3) that provide new information about activities that management wants to plan, evaluate, and control need to be included in such databases. None of the activities listed in the question satisfy these requirements. Customer information is stored in rows in the customer table and supplier data is stored in rows in the supplier table. The bulk of this would have been entered when the database was initially created and the customer and supplier tables created and populated. Subsequently, new rows would be entered in these tables as a by-product of other events that management does want to plan, evaluate, and control – such as a sales call, the receipt of an order from a new customer, or placing an initial order with a new supplier. Data processing activities, such as preparing reports or transcribing data from a form, are not explicitly modeled because they do not change information about any resources nor are they fundamental activities which management wants to control. (Consider: How often are managers concerned about how many reports a given employee prints in one day?) Indeed, all the information contained in a vendor invoice is already in the purchasing company’s database before the vendor invoice