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

number headings	title	aliases	tags
first-level 1, max 6, 1.1	redundancy-and-anomalies	redundancy and anomalies	info201

Redundancy

when values are stored repetitively in database relations

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

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

Anomalies

Update anomaly

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

Delete anomaly

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

Insert anomaly

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