# Basic Structure of realtional Database

## Basic Structure

- Figure 3.1 shows the
*deposit*and*customer*tables for our banking example.

**Figure 3.1:**The*deposit*and*customer*relations.- It has four attributes.
- For each attribute there is a permitted set of values, called the
**domain**of that attribute. - E.g. the domain of
*bname*is the set of all branch names.

Let denote the domain of

*bname*, and , and the remaining attributes’ domains respectively.Then, any row of*deposit*consists of a four-tuple whereIn general,

*deposit*contains a**subset**of the set of all possible rows.That is,

*deposit*is a subset ofIn general, a table of n columns must be a subset of

- Mathematicians define a relation to be a subset of a Cartesian product of a list of domains. You can see the correspondence with our tables.We will use the terms
**relation**and**tuple**in place of**table**and**row**from now on. - Some more formalities:
- let the tuple variable refer to a tuple of the relation .
- We say to denote that the tuple is in relation .
- Then [
*bname*] = [1] = the value of on the*bname*attribute. - So [
*bname*] = [1] = “Downtown”, - and [
*cname*] = [3] = “Johnson”.

- We’ll also require that the domains of all attributes be
**indivisible units.**- A domain is
**atomic**if its elements are indivisible units. - For example, the set of integers is an atomic domain.
- The set of all sets of integers is not.
- Why? Integers do not have subparts, but sets do – the integers comprising them.
- We could consider integers non-atomic if we thought of them as ordered lists of digits.

- A domain is