Must depend on the entity key alone Must contain information that we explicitly

Must depend on the entity key alone must contain

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Must depend on the entity key alone Must contain information that we explicitly need Must have the same data type for all entity occurrences
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Information Access Mgt 09/12/97 2 Discovering Entities Entities are normally described by NOUNS and ADJECTIVES Entities do not change anything. Entity occurrences are records, entity types are files. Reports are derived output and not entities.
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Information Access Mgt 09/12/97 2 Keys Names are normally poor primary keys. They have multiple valid representations. Primary keys: 1. Should not change values over the life of the instance. 2. Should not have null values. 3. Should not be "intelligent keys". These are keys that also describe properties of the entity. 4. Should not be large composite keys.
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Information Access Mgt 09/12/97 2 Not null vs nulls allowed Null values represent inapplicable, applicable but not known, and applicable but not present values. Primary keys cannot have null values. Null values are different from zeros or blanks
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Information Access Mgt 09/12/97 3 Diagrams: Attributes Entity Key . . . . . . Attribute Attribute
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Information Access Mgt 09/12/97 3 Diagrams: Repeating Groups Course SectionNum
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Information Access Mgt 09/12/97 3 PREMIERE PRODUCTS EXAMPLE The Premier Products Company is a wholesale hardware company that provides products to customers. Each customer is served by a salesman who processes orders. The salesmen is paid from commissions earned on each customer order. A customer places an order by calling the company and contacting the salesman. The salesman records the ordering person, products and quantity ordered.
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Information Access Mgt 09/12/97 3 PREMIERE PRODUCTS: REPEATING GROUPS In the Premier Products Company each salesmen is paid from commissions earned on each customer order. A customer places an order by calling the company and contacting the salesman. The salesman records the ordering person, products and quantity ordered. The order consists of Customer data, Salesman data
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  • Fall '16
  • jeoramedelubio
  • Entity-relationship model

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