Terminology

• Relation Scheme: list of attribute names.
  Example: R = (CID, CNAME, CITY, DISCOUNT).
• Domain: set of values.
  Example: set of integers, set of character strings of length 10, set of real numbers.
• With each attribute name A, we associate a domain referred to as domain(A).
  Example: domain(CID)=char4, domain(CNAME)=char13, domain(DISCOUNT)=integer
• A Tuple over the relation scheme (A1, ..., An) is (a1, ..., an) where each ai is an element of domain(Ai) or null.
  Example: ('c001','TipTop', 'Duluth',10) is a tuple over scheme R.
• Relation: over a relation scheme (A1, ..., An) is a finite set of tuples over the same scheme.
  Example: {('c001','TipTop', 'Duluth',10),('c002','Basics', 'Dallas',null)} is a relation over scheme R.

Basically,

• A relation over scheme R=(A1, ..., An) can be viewed as a table consisting of n columns and a finite set of rows.
• Each column corresponds to an attribute name and
• Each row corresponds to a tuple within the relation.

Relation         --- Table
Attribute Name   --- Column Name  
Tuple            --- Row