quartz/content/out/notes/normalisation.md

title	draft
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3 Normalisation

formal process of eliminanting unnecessary redundancy in relations by splitting relations into smaller chunks

bottom up approach

• functional dependencies ⇒ normalised relations
• requirements ⇒ conceptual ≫ logical is "top down"
• use normalisation to verify your logical design
  • to ensure you haven't missed anything

0.1 Pros ans cons

• frees from anomalies
• separates data the belong to different entities
• reduces data redundancy
• doesn't bias db design infaour of certain queries at the expense of others

• more relations required
• more complex queries can imply slower performance in some DBMSs

0.2 Normal forms

1NF ⇒ Single valued attributes only 2NF ⇒ all on-key attibutes fully dependent on PK (i.e., no dependencies on part of the PK) (no partial dependencies) 3NF/BCNF ⇒ no non-key transitive dependencies 4NF ⇒ no multivalued dependencies 5NF ⇒ all join dependencies implied by Composite key (CKs) 6NF ⇒ irreducible relations