Chapter 18 Implementing an REA Model in a Relational Database 18-1.

Chapter 18Implementing an REA Model in a Relational Database

18-1

18-2

Intergraded REA Diagram

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, 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.

18-3

Using REA Diagram to Create Relational Database

Advantage: Creating a set of tables from an REA

diagram automatically results in a well-structured relational database

Ensures the elimination of anomalies: Update Insert Delete

18-4

REA to Database Steps1. Create a table for each distinct entity in

the diagram and for each many-to-many relationship.

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.

3. 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. 18-5

• Our integrated diagram has seven event entities.

1

2

3

4

5

6

7

• Our integrated diagram has two resource entities.

1

2

1

12

2

3

3

3

3

3

3

• There are three distinct agent entities.• The first is the customer.• The second agent entity is the supplier.• The third agent entity is the employee. We label the types of

employees to make the diagram more understandable, but they all go in one table.

IMPLEMENTING AN REA DIAGRAM IN A RELATIONAL DATABASE

Total distinct entities to be represented in separate tables:

9

Table Types # Events 8Resources 2Agents 3Distinct Entities 12

7


Create a separate table to represent each many-to-many relationship in the conceptual model, I.e., for the following participation cardinality patterns (0,N)-(0,N) (0,N)-(1,N) (1,N)-(0,N) (1,N)-(1,N) You must create a separate table to represent the

relationship The primary keys of the related entity tables are posted into

the relationship table to form its primary key. This kind of primary key is called a composite or concatenated primary key

There are no exceptions to this rule!!!

If you post a foreign key in either direction, redundancy will be a problem for many-to-many relationships 10

Example: Many-Many Relationships(from DCH)

STUDENT COURSETAKES

(1,N) (1,N)

student #

name

address

course #

name

Student# Name Address

1 Tony Cleveland

2 Emily New York

3 Leigh Birmingham

Course# Name

Acg4401 AIS

Acg3101 FAR 1

Course# *

Acg4401, Acg3101

Acg4401, Acg3101

Acg4401, Acg3101

Student#*

1, 2, 3

1, 2, 3

11

Note: Each record field must be single valued(no repeating groups)

Example: Many-Many Relationship(from DCH)

STUDENT COURSETAKES

(1,N) (1,N)

student #

name

address

course #

name

Student# Name Address

1 Tony Cleveland

2 Emily New York

3 Leigh Birmingham

Course# Name

Acg4401 AIS

Acg3101 FAR 1

Student# Course#

1 Acg4401

1 Acg3101

2 Acg4401

2 Acg3101

3 Acg3101

Student-Course Relationship Table

12

• the many-to-many relationships.

1

2

3

4

5


Total number of tables in database:

Table Types #

Events 7

Resources 2

Agents 3

Distinct Entities 12

Many to many Tables 5

Total Tables 17

14


Identify primary keys Every table in a relational database must

have a primary key. The primary key is an attribute or

combination of attributes that uniquely identifies each row in a table.

It is typically a numeric identifier. The primary key is usually a single

attribute. However for M:N relationship tables, it

consists of two attributes that represent the primary key of each linked entity. These multiple-attribute primary keys

are called concatenated keys.

18-16

SALES

CASH RECEIPT

EMPLOYEESALES REP

CUSTOMER

EMPLOYEECASHIER

INVENTORY

CASH

Duality

Partic-ipation 3

Partic-ipation 4

Partic-ipation 5

Partic-ipation 6

Stockflow 1

Stockflow 2

Fred's Train Shop Revenue Cycle

(0,N)

(0,N) (0,N)

(0,N)

(0,N)

(0,N)

(1,1)

(1,1)

(0,1)

(0,N)

(0,N)

(1,1) (1,1)

(1,N)

Sale Order CUSTOMERPartic-ipation 1

Partic-ipation 2

(0,N)

(0,N)

(0,N)

(1,N)

(1,1)

(1,1)

(0,1)

(0,1)

C-Acct# C-BalType RA# TimeDate Pmt method

Emp# DOBDateHired

Pay Rate

Job Title

Cust# Cname CreditLimit

EmpName

Address

AcctBalanceDateSO# Time Comments

Date

Inv#

Time InvSent(Y/N)

Prod# DescList-Price

Std-cost

QOH QAvai

Reorder-Qty

Reorder-Pt

Qty Ordered

Qty Sold

Actual SalePrice

Amopunt Applied to

Invoice

Attribute assignment

17

AttributesTables Primary key Foreign Key(s) Other Attributes

SaleOrder SaleOrder# Date, Time, Comments

Sale Invoice# Date, Time, InvoiceSent(Y/N)

CashReceipt RA# Date, Time, PmtMethod

Inventory Product#Desc, ListPrice, StdCost, QtyonHand, QtyAvailable, ReorderQty, ReorderPoint

Cash Account # BegBalance, AcctType

Emoloyee Employee#EmpName, DateHired, DateBirth, PayRate, JobTitle

Customer Customer#Custname, Address, AccountBalance, CreditLimit

SaleOrder-InventorySaleOrder#, Product#

Sale-InventoryInvoice#, Product#

Sale-CashReceipt Invoice#, RA#

Tables for Fred’s Train

Shop Revenue

cycle

Use foreign keys to implement one-to-one and one-to-many relationships. Minimum cardinalities may suggest which

choice is more efficient. When there are two sequential events,

the primary key of the event that occurs first is usually the foreign key in the event that occurs second.

The primary key of the entity that can linked to multiple instances of the other entity must become the foreign key in that other entity. Example: The primary key for customer

(which can occur only once per sale) is a foreign key in the sales table (which can occur many times for a particular customer).

18

Example: (1,1)-(1,1)

SaleID Date Amount

S1 6/12 $10

S2 6/12 $15

S3 6/13 $12

CR-ID Date Amount

CR1 6/12 $10

CR2 6/12 $15

CR3 6/13 $12

CR-ID *

CR1

CR2

CR3

S-ID *

S1

S2

S3

Could do either one but because the entities represent sequential events, authors follow the practice of placing the primary key of the event that occurs first (sale) as a foreign key in the event that occurs second (cash receipt).

Sale Cash Receipt

yields(1,1) (1,1)

SaleID Date Amount CR-ID Date Amount

20

Example 2: Posting into a (1,1)-(0,1)

Sale Cash Receipt

yields

(1,1) (0,1)

SaleID Date Amount CR-ID Date Amount

SaleID Date Amount

S1 6/12 $10

S2 6/12 $15

S3 6/13 $12

CR-ID Date Amount

CR1 6/12 $10

CR2 6/12 $15

CR3 6/13 $12

CR4 6/13 $1,000

CR-ID*

CR1

CR2

CR3

S-ID*

S1

S2

S3

This eliminates null values

Example : Posting into a one to many

Sale CustomerIs-to

(1,1) (0,N)

SaleID Date Amount CustID NameCity

SaleID Date Amount

S1 6/12 $10

S2 6/12 $15

S3 6/13 $12

CincinnatiStevenC2

Walnut CreekHeatherC1

AddressNameCust-ID

Cust-ID*

C1

C2

C1

C3 Dave Cincinnati

S2

S1, S3

S-ID*

SALES

CASH RECEIPT

EMPLOYEESALES REP

CUSTOMER

EMPLOYEECASHIER

INVENTORY

CASH

Duality

Partic-ipation 3

Partic-ipation 4

Partic-ipation 5

Partic-ipation 6

Stockflow 1

Stockflow 2


(0,N)

(0,N) (0,N)

(0,N)

(0,N)

(0,N)

(1,1)

(1,1)

(0,1)

(0,N)

(0,N)

(1,1) (1,1)

(1,N)


Partic-ipation 2

(0,N)

(0,N)

(0,N)

(1,N)

(1,1)

(1,1)

(0,1)

(0,1)


Emp# DOBDateHired

Pay Rate

Job Title


EmpName

Address


Date

Inv#

Time InvSent(Y/N)


Std-cost

QOH QAvai

Reorder-Qty

Reorder-Pt

Qty Ordered

Qty Sold

Actual SalePrice

Amopunt Applied to

Invoice

18-22

Use foreign keys to implement one-to-one and one-to-many relationships

18-23


SaleOrder SaleOrder#Customer#, Employee#

Date, Time, Comments

Sale Invoice#SaleOrder#, Customer#, Employee#

Date, Time, InvoiceSent(Y/N)

CashReceipt RA#Customer#, Employee#, Account#

Date, Time, PmtMethod








Use foreign keys to implement one-to-one and one-to-many relationships

Foreign key (field property required or not required) If minimum cardinality for foreign key posting is

1(mandatory), field property attribute should be set to required

The six circled foreign key attributes field property should be set to required in the database table to avoid possibility of null value

SALES

CASH RECEIPT

EMPLOYEESALES REP

CUSTOMER

EMPLOYEECASHIER

INVENTORY

CASH

Duality

Partic-ipation 3

Partic-ipation 4

Partic-ipation 5

Partic-ipation 6

Stockflow 1

Stockflow 2


(0,N)

(0,N) (0,N)

(0,N)

(0,N)

(0,N)

(1,1)

(1,1)

(0,1)

(0,N)

(0,N)

(1,1) (1,1)

(1,N)


Partic-ipation 2

(0,N)

(0,N)

(0,N)

(1,N)

(1,1)

(1,1)

(0,1)

(0,1)


Emp# DOBDateHired

Pay Rate

Job Title


EmpName

Address


Date

Inv#

Time InvSent(Y/N)


Std-cost

QOH QAvai

Reorder-Qty

Reorder-Pt

Qty Ordered

Qty Sold

Actual SalePrice

Amopunt Applied to

Invoice

25

Foreign keys in bold red should have property attribute set to required to avoid null value.















26

Cardinalities indicate that Customer participation in relationship is mandatory.

Since it is mandatory, to avoid possible null value, make this attribute required in the sales table

Foreign key (required or not required)

There are 4 relationship attributes. If relationship becomes a separate table, then relationship

attributes are placed in that table If relationship established via foreign key, attribute placed in

table with foreign key

SALES

CASH RECEIPT

EMPLOYEESALES REP

CUSTOMER

EMPLOYEECASHIER

INVENTORY

CASH

Duality

Partic-ipation 3

Partic-ipation 4

Partic-ipation 5

Partic-ipation 6

Stockflow 1

Stockflow 2


(0,N)

(0,N) (0,N)

(0,N)

(0,N)

(0,N)

(1,1)

(1,1)

(0,1)

(0,N)

(0,N)

(1,1) (1,1)

(1,N)


Partic-ipation 2

(0,N)

(0,N)

(0,N)

(1,N)

(1,1)

(1,1)

(0,1)

(0,1)


Emp# DOBDateHired

Pay Rate

Job Title


EmpName

Address


Date

Inv#

Time InvSent(Y/N)


Std-cost

QOH QAvai

Reorder-Qty

Reorder-Pt

Qty Ordered

Qty Sold

Actual SalePrice

Amopunt Applied to

Invoice













QtyOrdered


QtySold, ActualSalePrice

Sale-CashReceipt Invoice#, RA# AmountAppliedtoInvoice 18-28

Relationship attributes

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

18-30

Chapter 18 Implementing an REA Model in a Relational Database 18-1.

Documents

Transcript of Chapter 18 Implementing an REA Model in a Relational Database 18-1.