quartz/content/notes/normalisation.md

title	aliases	tags
normalisation		info201

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

1 Pros and 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

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