Week 4
4.1 The Relational Data Model
Proposed by Edgar F. Codd (IBM) in 1970, the relational model represents data as a collection of TABLES (relations). It is the most widely used data model today and forms the basis of SQL databases.
KEY TERMINOLOGY:
|
Formal Term |
Common Term |
Description |
|
Relation |
Table |
A two-dimensional table with rows and columns |
|
Tuple |
Row / Record |
A single data instance in a relation (one student, one order, etc.) |
|
Attribute |
Column / Field |
A named property of the relation (StudentName, Age, etc.) |
|
Domain |
Data Type |
The set of permissible values for an attribute (e.g., integer 0-100 for Score) |
|
Degree |
Number of columns |
The number of attributes in a relation |
|
Cardinality |
Number of rows |
The number of tuples currently in a relation |
|
Schema |
Table definition |
The structure of the relation: name + list of attributes with domains |
EXAMPLE: STUDENT Relation (Table):
|
MatricNo (PK) |
StudentName | Department |
Level | GPA |
|
23B/UE/BCSX/1001 |
Habibullah Ladan | Cyber Security |
400 | 4.15 |
|
23B/UE/BSE/10011 |
Fatima Abdullahi | Software Engineering |
200 | 3.87 |
|
23B/UE/BICT/10023 |
Fatima Musa | Information Technology |
300 | 3.52 |
|
23B/UE/BNS/2001 |
Amina Bello | Nursing Science |
100 | 4.50 |
Properties of a valid relation: (1) Each cell contains exactly one value (atomic). (2) Each column has a unique name. (3) All values in a column are of the same domain. (4) Each row is unique, no two tuples are identical. (5) The order of rows and columns does not matter.