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CHAPTER 16 IMPLEMENTING AN REA MODEL IN A RELATIONAL DATABASE INTRODUCTION Questions to be addressed in this chapter: How are REA diagrams for individual transaction cycles integrated into a single comprehensive organization-wide REA diagram? How are tables constructed from the REA model of an AIS in a relational database? How can queries be written to retrieve information from an AIS relational database built according to the REA data model? INTEGRATING REA DIAGRAMS ACROSS CYCLES The previous chapter covered development of an REA diagram for an individual transaction cycle. This chapter demonstrates how to implement an REA diagram in a database. We focus on relational databases because they are commonly used to support transaction-processing systems and they are familiar to most business students. But REA modeling can also be used to design object-oriented databases. In Chapter 15, we looked at REA diagrams for the revenue and expenditure cycles. Before we integrate these diagrams with the payroll cycle, let’s take a look at the HRM/payroll cycle activities. HUMAN RESOURCE/PAYROLL CYCLE The basic economic exchange is: get employee time and skills; give a paycheck. The record time worked event must be linked to a particular employee and supervisor and will have a cardinality with a minimum and maximum of one. However, each agent can be linked to zero or many record time worked events. The zero minimum allows for inclusion of a new employee or supervisor who has not yet been involved in a time recording. A similar situation exists with the disburse cash event. (We regard each individual paycheck as a separate cash disbursement.) The assumption is made that employees record time worked on a daily basis. Record time worked is therefore linked to a maximum of one cash disbursement , since employees aren’t paid for half a day on one paycheck and the other half of the day on Chapter 16: Implementing an REA Model in a Database 1 Employees Employee (Payroll Clerk) Employee (Supervisor) Record Time Worked Disburse Cash Employee Time Cash
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another check. For each cash disbursement , however, there are one-to-many record time worked events. In other words, a paycheck could pay an employee for anywhere from one day’s work to many. With respect to the employee time entity, the resource being acquired by the record time worked event is the use of an employee’s skills and knowledge for a period of time. Time is different from other resources in that it cannot be stored. The relevant attributes about employee time are hours worked and how the time was used, and these attributes are captured by the record time worked and disburse cash events. So, the employee time resource entity is almost never implemented in an actual database, which is why it is depicted with dotted lines. The relationship between
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