The Relational Model for Database Management Version 2 - Notes (0)

[Chapter 1]

A Relation R in the Relational Model has the following properties:
(1) Each row represents a tuple of R.
(2) The ordering of rows is immaterial.
(3) All rows are distinct from one another in content.

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on Relations in Mathematics Vs Relations in the Relational Model:

(1) Unconstrained values in Mathematics while atomic values in the Relational Model.
(2) Columns are not named in Mathematics while each column is named in the Relational Model.
(3) Columns are distinguished by position in Mathematics while distinguished by name in the Relational Model.
(4) Normally constant in Mathematics while varies with time in the Relational Model.

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* The terms "Table" and "Relation" are not synonyms. (why?)
* The relations in the Relational Model are a special kind of tables called R-tables.
* R-tables have no positional concepts. there is not "nextness" of rows or columns.
* duplicate rows are not allowed in all relations.

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on Terminology:

* A Relation of degree n in Mathematics is an R-table with n columns in the Relational Model.
* An Attribute in Mathematics is a Column of R-table in the Relational Model.
* A Domain in Mathematics is an Extended data type in the Relational Model.
* A Tuple in Mathematics is a Row of R-table in the Relational Model.
* The Cardinality of the relation in Mathematics is the number of rows in R-table in the Relational Model.