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REA analysis and E-R diagramming

REA analysis and E-R diagramming. Database Applications. Phase 1 Flat Files. Phase 2 Event-Driven Database. Phase 3 REA-Model Database. Limitations: Not widely used; Requires detailed analysis. Limitations: Redundant data; Anomalies. Limitations: Loss of non-economic information.

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REA analysis and E-R diagramming

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  1. REA analysis and E-R diagramming

  2. Database Applications Phase 1 Flat Files Phase 2 Event-Driven Database Phase 3 REA-Model Database Limitations: Not widely used; Requires detailed analysis Limitations: Redundant data; Anomalies Limitations: Loss of non-economic information

  3. 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 are we hoping to achieve?

  4. 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? What are we hoping to achieve?

  5. Entities • Relations • Events • Resources • Agents • Locations • Concatenated keys • Cardinality Some of the usual suspects…

  6. 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 Resource-Event-Agent modeling

  7. 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? Resource-Event-Agent(-Location) analysis and modeling

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

  9. Location Event External Agent Resources Internal Agents Who What Where

  10. 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 Entity-Relationship diagramming

  11. Resource Internal agent Event Location (if needed) External Agent (if needed) Entity-Resource-Agent modelingbasic template Resource Internal agent These are all considered entities Event Location (if needed) External Agent (if needed)

  12. Sold by decreases Sold to Takes place at Results in Received from Takes place at Collects payment increases Entity-Resource-Agent modelingExample Salesperson Merchandise Sell Merchandise Customer Cash Register Receive Customer payment Cash Now we add relations

  13. Sold by decreases Sold to Takes place at Results in Received from Takes place at Collects payment increases Entity-Resource-Agent modelingwith diamonds Salesperson Merchandise Sell Merchandise Customer Cash Register Receive Customer payment Cash

  14. Give-To- Get Duality The REA Data Model Resources Events Agents

  15. The REA Data Model Resources: Those things that have economic value to the firm. Resources Events Agents

  16. The REA Data Model Events: Various Business Activities Resources Events Agents

  17. The REA Data Model Agents: People and Organizations that participate in events. Resources Events Agents

  18. Entity-Resource-Agent modeling • 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 Entity Relationship • Describes how two entities relate Attribute • Specifies an entity (a record)

  19. 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 Entity-Relationship diagrams

  20. Entity-Relationship modeling

  21. tblCashDisbursementCheck No. tblCashDisbursementInventoryReceipt Inv Rec No. + Chk No Check No. Date tblInventoryReceiptInv Rec No Inv Receipt No. PONo. tblPurchaseOrderPO No. tblPOInventoryReceiptPO No. + Inv Stck No. tblMaterialsInventoryInv. Stck No PONo. VendorNo. Inv Stock No. Inventory data tblVendorVendor No. Vendor data Entity-Relationship modeling

  22. Entity-Relationship modeling tblCashDisbursementCheck No. tblCashDisbursementInventoryReceipt Inv Rec No. + Chk No Check No. Date tblInventoryReceiptInv Rec No Inv Receipt No. PONo. tblPurchaseOrderPO No. tblPOInventoryReceiptPO No. + Inv Stck No. tblMaterialsInventoryInv. Stck No PONo. VendorNo. Inv Stock No. Inventory data tblVendorVendor No. Vendor data

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