Relation View

A relation is a set of tuples

• tuples must have same degree
• tuples can not repeat information
• tuples data must be consistent

A schema is the name of a relation and name(s) of attributes

key: atrribute(s) with values that are unique across all tuples in a relation

EX Parts, Projects, Commitments as Peers

Parts (Part #, Name, Qty On Hand) <– Relation Schemas

• Part 1, Bolt, 1000 on hand
• Part 2 Electrical Wiring 500ft on hand

Projects (Project ID, Name)

• Project A/ Apollo 8
• Project B / Apollo 10
• Project C / Apollo 11

Commitment (Part, Project, Qty Committed) <- (part, project) forms a composite key

• Part 1 / Project A/ 100
• Part 1 / Project A/ 5 / Project B / 15
• Part 1 / Project A / 100
• Part 2 / Project A / A dozen
• Part 1 / Project A / 158
• Part 9 / Project XYZ / 50

Commitment.Part is a foreign key referencing Parts.Part #

• must reference a key

Commitment.Project is a foreign key referencing Projects.Proj ID