Relational Database Principles

The mathematical principles of relations are few and simple:

• A relation is a matrix of tuples (rows) and domains (columns).
  
• This means all tuples in a given relation have the same domains.
  
• The (theoretical) location of any tuple is unknown. Thus a tuple can be retrieved only by its content and not by any address.
  
• All information in and about a relational database is contained in relations in the database.
  
• New relations can be construced from other relations by joins.