Relational Model- Structure

Question 1

The scalar

Answer 1

The smallest semantic unit of data. It’s the smallest piece of data that has meaning

Question 2

Domain

Answer 2

A named set of scalar values, all of the same type.
In the context of relational models: domains are pools of values from which actual attribute values are drawn

Domains are more than data types given nowaday.

E.g. domain of all possible cities in the world

Question 3

Relation (remember)

Answer 3

• set of attributes (heading) -> attribute name; domain name pairs
• set of tuples (body) -> set of attribute - name, attribute - value pairs

Question 4

Relation(definition)

Answer 4

A relation consists of a heading and a body.
The heading is a set of attributes, where each attribute is associated with a domain.
The body is a set of tuples, where each tuple is a set of attribute values.

The attribute values come from the domain that’s associated with that attribute’s name in the heading.

Question 5

NB point about Atomicity.

Answer 5

Attribute values are scalar.
You can only have one thing in a place

Question 6

Properties of relations

Answer 6

1. There are no duplicate tuples
2. Tuples are unordered, top to bottoms
3. Attributes are unordered, left to right

(1-3 important for data independence)

All attribute values are atomic (can only come from domains of scalar values so they will always be atomic)

Question 7

Table vs Relation

Answer 7

Relations are abstract objects. They are good to express the idea of what is happening in the database.

Tables are the actualisation of the models in the relational database