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Understanding Entity-Relationship Diagrams (ERDs): A Guide to Business Relationships

Entity-Relationship Diagrams (ERDs) are vital tools for modeling the relationships between entities within a system. Entities can be thought of as "nouns" that a business tracks, such as Vehicles, Customers, or Vendors, while relationships are the "verbs" connecting them, like Receive and Assign. Cardinality identifies the numerical mapping between entities, which can vary from one-to-one to many-to-many, influencing business rules. This guide provides examples and highlights the importance of accurately defining and documenting these relationships for effective information management.

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Understanding Entity-Relationship Diagrams (ERDs): A Guide to Business Relationships

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  1. Entity Relationship Diagrams (ERDs)

  2. Entity Relationship Diagram (ERD) • documentation technique to represent relationship between entitiesin system. • Think of entities as “nouns” – nouns on which a company would want to track information. A few examples: • Vehicles • Accounts Receivable • Customers • Vendors

  3. Entity Relationship Diagram (ERD) • Think of the relationship as a “verb” • The verb connects (relates) one entity to another. A few examples: • Receive • Assign • Prepare • Send

  4. Depends on business rules !! Cardinality between entities • represents the numerical mapping between entities: • one-to-one • one-to-many • many-to-many

  5. Cardinalities Entity Relationship Entity 1 1 Sales- person Car is assigned Customer Company A

  6. Cardinalities Entity Relationship Entity 1 M Sales- person Car is assigned Company B Customer

  7. Cardinalities Entity Relationship Entity 1 M places Order Customer This cardinality is probably true for most businesses.

  8. Cardinalities Entity Relationship Entity M M Vendor Inventory supplies This cardinality would depend on the business.

  9. ERD – Expenditure Cycle

  10. Describe the business rules represented by the cardinalities in the ERD. VENDOR 1 1 M M P.O. M INVENTORY M 1 M M REC. RPT. 1

  11. Add 3 attributes for each entity. VENDOR 1 1 M M P.O. M INVENTORY M 1 M M REC. RPT. 1

  12. 3 attributes for each entity. VENDOR 1 M 1 M P.O. M INVENTORY M 1 M M REC. RPT. 1

  13. Modify the ERD, based on the following information: 1 The Vendor sends an invoice for each shipment.The invoice is matched tothe RR; a Cash Disbursement (CD) is prepared for each invoice. VENDOR 1 M M M P.O. M INVENTORY 1 M M 1 REC. RPT. 13

  14. VENDOR 1 1 M M P.O. M INVENTORY M 1 M M REC. RPT. 1

  15. Add 3 attributes for each new entity. VENDOR 1 1 M M P.O. M INVENTORY M 1 M M REC. RPT. 1

  16. The End

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