Chapter 18 Implementing an REA Model in a Relational Database Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 18-1
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Chapter 18
Implementing an REA Model in a Relational Database
Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 18-1
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 18-2
REA Diagram—Revenue Cycle
18-3
Make Sale
REA Diagram—Expenditure Cycle
18-4
REA Diagram—Payroll Cycle
18-5
Get Time
REA Redundancies
Separate REA for an organization will have redundant entities Resource
Each resource entity must be connected to: The resource entity is linked 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
Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 18-6
REA Redundancies
Events and Agents Alters the minimum cardinalities
associated with the other events that are related to the merged events or agents May be linked to either an event or agent
that is part of one business cycle or to an event or agent that is part of another cycle but cannot be linked to both events or agents at the same time The minimum cardinality associated with the other
events and agents must be 0 in the integrated REA diagram
Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall 18-7
Make Sale
Get Time
Integrated REA Diagram
18-8
Revenue
Cycle
Cardinality Effect of Merging Resources
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Cardinalities between resource and entities remain the same.
Make Sale
Cardinality Effect of Merging Events
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The cardinality between Disburse Cash and Supplier and Employee (as payee) is now 0 to 1, that is, a disbursement can be made to the supplier or the employee but not both!
Cardinality Effect of Merging Events
Copyright 2012 Pearson Education, Inc. publishing as Prentice Hall 18-11
The cardinality between Disburse Cash and Supplier and Employee (as payee) is now 0 and 1, that is, a disbursement can be made to the supplier or the employee but not both!
The cardinality between Disburse Cash and Receive Inventory and Time Worked is now 0 and 1, that is, a disbursement can be made to the for Accounts Payable (Receive Inventory) or Payroll (Time Worked) but not both!
Get Get TimeTime
Disburse Disburse CashCash
Receive Receive InventoryInventory
SupplierSupplier
Employees Employees (Cashier)(Cashier)
Employees Employees (as Payee)(as Payee)
Employees Employees
Rules for Creating Integrated REA Diagram
1. Every event must be linked to at least one resource.
2. Every event must be linked to two agents who participate in that event.
3. Every event that involves the disposition of a resource must be linked to an event that involves the acquisition of a resource.
4. Every resource must be linked to at least one event that increments that resource and to at least one event that decrements that resource.
5. If event A can be linked to more than one other event or agent, but cannot be linked simultaneously to all of those other events or agents, then the REA diagram should show that event A is linked to a minimum of 0 of each of those other events or agents.
18-12
Using REA Diagram to Create Relational Database
Advantage: Ensures the elimination of anomalies:
Update Insert Delete
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REA to Database Steps
1. Create a table for each distinct entity in the diagram and for each many-to-many relationship.
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REA to Database Steps
2. Assign attributes to appropriate tables. Identify primary keys:
Attributes 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.
Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall 18-15
REA to Database Steps
3. Use foreign keys to implement one-to-one and one-to-many relationships.
1:1 Relationships Choice of which table to place foreign key is
arbitrary, Often if events are sequential, the foreign key is
placed in the later event of the sequence, 1:M Relationships
Primary key of entity that can be linked to multiple instances of the other will become the foreign key in the other table.
Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall 18-16
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
Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 18-17
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