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31 lines
1.0 KiB
Markdown
31 lines
1.0 KiB
Markdown
---
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title: Normalisation
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draft: true
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---
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# 3 Normalisation
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formal process of eliminanting unnecessary redundancy in relations by splitting relations into smaller chunks
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bottom up approach
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- functional dependencies ⇒ normalised relations
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- requirements ⇒ conceptual ≫ logical is "top down"
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- use normalisation to verify your logical design
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- to ensure you haven't missed anything
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### 0.1 Pros ans cons
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+ frees from anomalies
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+ separates data the belong to different entities
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+ reduces data redundancy
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+ doesn't bias db design infaour of certain queries at the expense of others
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- more relations required
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- more complex queries can imply slower performance in some DBMSs
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### 0.2 Normal forms
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1NF ⇒ Single valued attributes only
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2NF ⇒ all on-key attibutes fully dependent on PK (i.e., no dependencies on part of the PK) (no partial dependencies)
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3NF/BCNF ⇒ no non-key transitive dependencies
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4NF ⇒ no multivalued dependencies
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5NF ⇒ all join dependencies implied by Composite key (CKs)
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6NF ⇒ irreducible relations |