quartz/content/notes/redundancy-and-anomalies.md

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Redundancy and Anomalies	true

1 Redundancy and Anomalies

0.1 Redundancy

when values are stored repetitively in database relations

• usually in poorly designed relations
• • potential for anomalous data to be stored e.g.,

0.1.1 How it arises

• ad hoc database
  • flat file
  • spreadsheet (no contraints)
• Poor database design
  • poor analysis
  • poorly designed ERDs (not thinkiing properly about the relationships)
• modifications to existing systems
  • "bolting on" new attributes
  • schema evolution over time

0.2 Anomalies

0.2.1 Update anomaly

An anomaly that occurs follows an UPDATE operation e.g.,

0.2.2 Delete anomaly

An anomly that occurs following a DELETE operation e.g.,

0.2.3 Insert anomaly

An anomly that occurs following a INSERT operation e.g., Causes the process of putting johnson in system is delayed