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ch4 - • If do not have two unique fields can combine two...

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AIS Chapter 4 Relational Databases Entity-anything the firms wants to record data about o Resources o Events o Agents Attributes-details of the entities-stored in fields (columns = fields) Record-all the fields containing data about one entity (row = record) File-a set of all related records Interrelated, centrally located files form a database Problems with master files: o Redundant o Costly o Same problem as having paper files, sometimes there are duplicate files, and if one gets updated, the other may not Database manages all departments’ files Database management system Primary key: attribute; uniquely identifies a specific row Cannot have duplicate primary keys o Good primary key: social security numbers
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Unformatted text preview: • If do not have two unique fields, can combine two fields to make one unique primary key • Foreign key is an attribute that is a primary key in another table • All tables have to be linked somehow • Uniform table problems: o Update anomaly o Insert anomaly • Null values are not good; try to have info in each space o Delete anomaly • Basic requirement o Every column has a single value • Primary key cannot be null, mist be unique o Entity Integrity rule • Foreign key can be either null or be primary key of another table o Referential Integrity rule • All non-key should describe a characteristic of object identified by the primary key...
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