As an example of relations among discrete objects, we present a brief introduction to a relational model for data bases. Modern large-scale computing systems are capable of handling large amounts of data, such as the records of charge account transactions of customers in a department store, the employment history and personal data of employees in a company, and the records of parts ordered and received in a factory. So that large amounts of data can be handled effectively, they must be organized in some form suitable for the more frequent operations, such as inserting new data, deleting old data, updating existing data, and searching for items with special attributes. One general way to view the organization of large varieties of data is with a relational data model. Let A₁, A₂, …., A_n be n (not necessarily distinct) sets. An n-ary relation among A₁, A₂, … , A_n is known as a table on A₁, A₂, …. A_n in the language of relational data models. The sets A₁, A₂, ….., A_n are called the domains of the table, and n is called the degree of the table. For example, let SUPPLIER = {s₁, s₂, s₃, s₄} be the set of suppliers of parts, PART = {p₁, p₂, p₃, p₄, p₅, p₆, p₇} be the set of parts, PROJECT = (ƒ₁, ƒ₂, ƒ₃, ƒ₄, ƒ₅} be the set of projects, and QUANTITY be the set of positive integers. We may have a table named Supply on the sets SUPPLIER, PART, PROJECT, and QUANTITY describing the names of suppliers who supply parts to the various projects and the quantities they supply. Thus,

SUPPLY = {(s₁, p₂, j₅, 5), (s₁, p₃, j₅, 17), (s₂, p₃, j₃, 9), (s₂, p₁, j₅, 5), (s₄, p₁, j₁, 4)}

SUPPLIER	PART	PROJECT	QUANTITY
s1	p2	j5	5
s1	p3	j5	17
s2	p3	j3	9
s2	p1	j3	5
s4	p1	j1	4

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