# SQL Database
- Database is a collection of related data.
- Data is: known facts that can be recorded and have implicit meaning.
- Database is a collection of values in digital form, organized in a efficient way

## Data modeling

Data model is a collection of concepts to describe the structure of a database.

Structure of a database includes data types, relationships and constraints that apply to the data.

- High Level: Conceptual data models
- Low Level: Physical data models
- Representational: implementational data models

## Conceptual Data Model

Conceptual data models use concepts such as: entities, attributes and relationships.

An entity represents a real-world object or concept. Examples are: Employee, Product, etc...

## Entity

An entity contains attributes that have values. For example, an entity Person may have the following attributes: Name, Age, Sex, etc..

## Entity Set

A entity set is a collection of entities that share the same attributes. The entities within the set are distinguishable from each other because the values that the attributes have differ.