The Relational Model

1
The Relational Model

• Pratt Adamski, Chapter 2

2
Relational Algebra

• Project
• Select
• Join

• Union
• Intersect
• Subtract
• Product
• Division

3
Relational Database

• Based in formal set theory
• Most common data structure
• Provable design principles

4
Relational Definition

• Relations
• Attributes
• Relationships
• Operations

5
Relation
Attributes
Occurrences or Tuples
6
Relation Requirements

• Attributes are single valued, and all entries
  have the same data type
• Each attribute has a distinct name
• All values in a column are values of the same
  attribute
• The order of columns is irrelevant
• Each row is distinct
• The order of rows is irrelevant

7
Premiere Products Example
8
Row OperationsSelect, Project, Join

• SELECT returns desired rows
• PROJECT returns desired columns
• JOIN creates one table from two by matching
  specified column values in the two tables

9
Set OperationsUnion, Intersection, Difference

• Returns the union, intersection, or difference
  of rows in two tables
• Note both tables must be union compatible.
  They must have the same number of columns and the
  corresponding columns must have the same data
  types.

10
Table OperationsProduct, Division

• PRODUCT (Cartesian product) produces a table with
  the columns of both tables and rows consisting of
  all combinations of rows from the two tables. If
  table A has m rows and table B has n rows, the
  product will have mn rows.
• DIVISION (A divided by B where the columns in B
  are also in A) produces a table consisting of
  columns in A that are not in B and match all the
  rows in B.