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44 lines
1.1 KiB
Markdown
44 lines
1.1 KiB
Markdown
---
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number headings: first-level 1, max 6, 1.1
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title: "redundancy-and-anomalies"
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aliases: redundancy and anomalies
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tags:
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- info201
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---
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# 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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## 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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# Anomalies
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## Update anomaly
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An anomaly that occurs follows an UPDATE operation
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e.g.,
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## Delete anomaly
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An anomly that occurs following a DELETE operation
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e.g.,
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## 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
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