Implementing an REA Model in a Relational Database Chapter 6 Implementing an REA Model in a Relational Database Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall

Learning Objectives Integrate separate REA diagrams for individual business cycles into a single, comprehensive organization-wide REA diagram. Build a set of tables to implement an REA model of an AIS in a relational database. Explain how to write queries to retrieve information from an AIS relational database built according to the REA data model. Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall

REA Diagram – Revenue Cycle Redundant Redundant Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall

REA Diagram – Expenditure Cycle Redundant Redundant Redundant Copyright 2012 Pearson Education, Inc. publishing as Prentice Hall

REA Diagram – Payroll Cycle REA is in mirror form, Agent, Event, Resource Get/Give Time Worked/Disburse Cash Give/Get Time Used/Bill Client Each Event should be related to one Resource But Time Worked is usually NOT Time can NOT be increased/decreased Attributes stored in Time Event Hours Worked Time Used Redundant Redundant Copyright 2012 Pearson Education, Inc. publishing as Prentice Hall

REA Redundancies Separate REAs for an organization will have redundant Entities Eliminate (merge) the Redundant Resource Entities Eliminate Redundant Resources (no duplicates): Link Resources to event entities in one business cycle and to event entities in the other cycle One Event that Increases the Resource and, One Event that Decreases the Resource No effect on Cardinality Redundant Event Entities Eliminate (Merge) the Redundant Event Entities alters the minimum cardinalities associated with the other events that are related to the merged event if: the merged event may be linked to either an event that is part of one business cycle or to an event that is part of another cycle but cannot be linked to both events. the minimum cardinality associated with the other events must be 0 in the integrated REA diagram May alter minimum cardinality between Event and Agent if: if agents are different in different transaction cycles Minimum becomes 0 (optional) Copyright 2012 Pearson Education, Inc. publishing as Prentice Hall

REA Redundancies Agents If Duplicate Agents exist across transaction cycles Do NOT eliminate them, keep them for legibility of the model Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall

Rules for Creating Integrated REA Diagram Every event must be linked to at least one resource. Every event must be linked to two agents who participate in that event. Every event that involves the disposition of a resource (give event) must be linked to an event that involves the acquisition of a resource (get event). Every resource must be linked to at least one event that increments that resource (Get) and to at least one event that decrements that resource (Give). If event A can be linked to more than one other event, but cannot be linked simultaneously to all of those other events, then the REA diagram should show that event A is linked to a minimum of 0 of each of those other events. If event A can be linked to more than one other agent, but cannot be linked simultaneously to all of those other agents, then the REA diagram should show that event A is linked to a minimum of 0 of each of those other agents. Copyright 2012 Pearson Education, Inc. publishing as Prentice Hall

Integrated REA Diagram Expenditure Cycle Revenue Cycle Payroll Cycle Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall

Cardinality Effect of Merging Resources Cardinalities Between Resource and Entities Remain the Same. Copyright 2012 Pearson Education, Inc. publishing as Prentice Hall

Cardinality Effect of Merging Events The Cardinality Between Disburse Cash and Receive Inventory and Disburse Cash and Time Worked is now 0 The Cardinality between Disburse Cash and Supplier & Employee (as payee) is now 0 to 1, that is a disbursement can be made to the supplier OR the employee but not BOTH! Copyright 2012 Pearson Education, Inc. publishing as Prentice Hall

Using REA Diagram to Create Relational Database Advantage: Ensures the elimination of Anomalies: Update Insert Delete Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall

REA to Database Steps Create a table for each distinct entity in the diagram and for each many-to-many relationship. Assign attributes to appropriate tables. Identify Primary Keys Attribute(s) that uniquely identifies each record For M:N relationships the primary key consists of two attributes that represent the primary keys of each entity linked in that relationship. Identify remaining attributes for Table. Use foreign keys to implement one-to-one and one-to-many relationships. an attribute of one entity that is itself the primary key of another entity. 1:1 If events are sequential, the Primary Key of the 1st event should be used as the Foreign Key of the 2nd event If not sequential, either entities primary key can become the foreign key of the other table 1:N Primary Key of the Entity Linked to the Many Entity MUST be used as the Foreign Key in the Many Entity Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall

Step 1 Event Tables Create Tables for each Entity Create Table for each M:N Maximum Cardinality Resource Tables 12 tables from Entities 5 tables from M:M cardinalities Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall

Step 3 1:1 Primary key of 1st chronological event should be foreign key of next event. Order# FK in Sales 1:N Primary key of entity linked to many event, becomes foreign key in many event Supplier# FK in Order Inventory Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall

Retrieving Information from REA Database Journals Information contained in Event tables Ledgers Information contained in Resource tables Financial Statements Information contained in Resources and Information on imbalances Accounts receivable sales transactions for which customer payments have not yet been received Accounts payable purchases from suppliers that have not yet been paid for Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall