Hamish Burke | 2025-03-12

Related to: #databases

Relational Model of Data

Introduced in 1970
RDM represents the database as a collection of relations
Finite relations are sets of tuples (or records)
Enables physical data independence
Relation schema
- Corresponds to Entity Type in Entity-Relationship Model

Relation Schema

$N (A_{1} : D_{1}, . . ., A_{n} : D_{n}, C)$

SUPPLIER(Supplier_no: INT, Name: STRING, Address: STRING)

S t u d e n t ({i d : S t r i n g, I n a m e : S t r i n g, F n a m e : S t r i n g, m a j o r : S t r i n g}, {i d})

The degree of the SUPPLIER relation is 3 (number of attributes)
$N$ is the name of the relation
$A_{n}$ are attributes
Each attribute has a domain $D$ or a set of valid values
And a set of constraints $C$ defined on it

Relation schema key $K$

AKA minimal key or a key

Has to be
- Unique
  - for all relations, for every tuple, if they agree on the values over $X$ , they are the same tuple ( $X$ being the potential schema key)
- minimal
  - For all proper subsets $Y$ of $X$ , the uniqueness property does not hold
- not null
  - because we use this to identify individual tuples
    Primary Key $K_{p}$
A key used in UoD for identification most frequently

Entity Integrity Constraint

No primary key values can be null

Foreign Keys

To connect the relation schema's
May contain null values

P E R S O N ({N a m e, B i r t h d a y, A d d r e s s}, {N a m e + B i r t h d a y})

S T U D E N T ({I D, N a m e, B i r t h d a y}, {I D})

Define foreign key on student: $S T U D E N T [N a m e, B i r t h d a y] subset P E R S O N [N a m e, B i r t h d a y]$