quartz/content/notes/databases.md

title	aliases	tags
databases		cosc203

Modelling

Database: integrated collection of data

• meaning
• specific purpose

ER Diagram Schemas

Relational Model

Two parts

• Relation Schema
• Domain

Constraints

• Domain: each value must an atomic value in the domain e.g., integer, string, date, etc
• Key and NULL:
  • Superkey: uniquely ids a tuple e.g., set of all attrs
  • Key: minimal superkey
  • Candidate key: a possible key
  • Primary key: the chosen candidate key: cannot have NULL values
• Ref Integrity: Foreign key
• Functional Dependencies
  • fd: when one value determines another e.g., sid -> sname, {sid, cid} -> grade
  • armstrong axioms:

Normal Forms

Normal Forms

SQL

SQL