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40 lines
1.1 KiB
Markdown
40 lines
1.1 KiB
Markdown
---
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title: Redundancy and Anomalies
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draft: true
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---
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# 1 Redundancy and Anomalies
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### 0.1 Redundancy
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when values are stored repetitively in database relations
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- usually in poorly designed relations
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- - potential for anomalous data to be stored
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e.g., 
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#### 0.1.1 How it arises
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- ad hoc database
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- flat file
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- spreadsheet (no contraints)
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- Poor database design
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- poor analysis
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- poorly designed ERDs (not thinkiing properly about the relationships)
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- modifications to existing systems
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- "bolting on" new attributes
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- schema evolution over time
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### 0.2 Anomalies
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#### 0.2.1 Update anomaly
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An anomaly that occurs follows an UPDATE operation
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e.g.,
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#### 0.2.2 Delete anomaly
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An anomly that occurs following a DELETE operation
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e.g.,
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#### 0.2.3 Insert anomaly
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An anomly that occurs following a INSERT operation
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e.g.,
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Causes the process of putting johnson in system is delayed |