Databases & Consistency

Database Relational databases : dominant information storage/retrieval system

Database Data stored in tables – Each row is a record – Columns define attributes

Queries Interact with DB's via queries – SELECT : retrieve some data

Queries Interact with DB's via queries – UPDATE : modify some data

Normalized Data A table of goals scored in soccer matches…

Repetitive Data A table of goals scored in soccer matches… Massive duplication of information about one game – Wasteful – Hard to modify

Normalized Data Goal : represent each piece of data only once – Break into separate tables

Normalized Data Keys : values used to rapidly look up info in other tables

Virtual Table Trick Given these two tables determine who scored on Greece:

Virtual Table Trick Join : merge two tables based on keys

Virtual Table Trick Projection : throw away columns we don't need

Virtual Table Trick Select: throw away rows we don't need

Virtual Table Trick Select: throw away rows we don't need

Virtual Table Trick Projection : throw away columns we don't need