Phase 1Flat Files

Phase 2Event-Driven Database

Phase 3REA-ModelDatabase

Limitations:Redundant data;Anomalies

Limitations:Loss of non-economic information

Limitations:Not widely used;Requires detailed analysis

Database Applications

Tool for designing a database system to meet the needs of the organization or the system - if you are not considering an

enterprise wide system (ERP). REA modeling (ERA modeling, REA

analysis, etc.) is a method of analyzing and thinking about the system

E-R diagramming is a means of diagramming what the database should look like based upon the analysis above.

What we want to do is follow a structured approach for designing databases.

The basic element in a database is called an entity - What do you think an entity might be

relative to an ACCESS database?

Entities Relations Events Resources Agents Locations Concatenated keys Cardinality

REA modeling is a hot topic in systems circles It has gone through several name/content variations

ERA modeling (more of a focus on events - typically this is the way it is done - but the name is not as easy to remember)

REAL Resources Events Agents Locations

Some books combine REA and E-R diagramming and some make no distinction IT CAN GET CONFUSING

We focus on events, which are things that get recorded in our system

For each event we will possibly have The event itself Resources consumed or obtained Internal agents (entities) External agents (entities) Perhaps a location

The reason that the word entities is in parentheses is that with this type of modeling, all five of these things are referred to as “entities”.

This sounds a lot like narratives, DFDs and flowcharts, huh?

Think back to the purchase order in the SUA that we looked at a few days ago…

Where

Who

What

Sometimes called REA diagramming (a specific form of E-R)

It uses three symbols A rectangle

An entity (but not the same as in DFDs and flowcharts

A diamond A relationship

An oval An attribute

Event

ResourceInternalagent

Location(if needed)

ExternalAgent

(if needed)

Event

ResourceInternalagent

Location(if needed)

ExternalAgent

(if needed)

These are allconsideredentities

SellMerchandise

MerchandiseSalesperson

Customer

ReceiveCustomerpayment

Cash

CashRegister

decreases

increases

Takes place at

Takes place at

Collects payment

Sold by

Sold to

Received from

Resultsin

Now we add relations

SellMerchandise

MerchandiseSalesperson

CashRegister

Customer

ReceiveCustomerpayment

Cash

decreases

increases

Takes place at

Collects payment

Sold by

Sold to

Received fromTakes place atR

esul

ts

in

The REA Data Model

Resources Events Agents

Give-To- Get Duality

The REA Data Model

Resources Events Agents

Resources: Those things

that have economic value

to the firm.

The REA Data Model

Resources Events Agents

Events: Various

Business Activities

The REA Data Model

Resources Events Agents

Agents: People and

Organizations that participate

in events.

Entity

Relationship -Describes how two entities relate

Attribute -Specifies an entity (a record)

-Resource - such as merchandise or cash-Person (what we referred to as entities in DFDs)-Location (such as the cash register)

-Note that we never specified this before-Event

There is a distinction between REA modeling and E-R diagramming! This distinction is not really important,

though. E-R diagrams can be used to

graphically show the REA model This type of modeling is useful for

designing databases Notice that the

database/relationships design for the Ch03.mdb database looks very much like the ER diagram

tblCashDisbursementCheck No.

tblPurchaseOrderPO No.

tblCashDisbursementInventoryReceipt

Inv Rec No. + Chk No

tblInventoryReceiptInv Rec No

tblMaterialsInventoryInv. Stck No

tblVendorVendor No.

tblPOInventoryReceipt

PO No. + Inv Stck No.

CheckNo.

InvReceipt

No.

VendorNo.

PONo.

PONo.

InvStockNo.

Date

Inventory data

Vendor data

tblCashDisbursementCheck No.

tblPurchaseOrderPO No.

tblCashDisbursementInventoryReceipt

Inv Rec No. + Chk No

tblInventoryReceiptInv Rec No

tblMaterialsInventoryInv. Stck No

tblVendorVendor No.

tblPOInventoryReceipt

PO No. + Inv Stck No.

CheckNo.

InvReceipt

No.

VendorNo.

PONo.

PONo.

InvStockNo.

Date

Inventory data

Vendor data