Data Modeling - Relationships

1 - About

The relationship is the core aspect of a relational database.

For instance, a many-to-one relationship is a link between two entities when one entity has a foreign key that references the primary key of another entity.

All relationships are implicitly bidirectional, meaning that they can interpreted in both directions.

When you have foreign key that NOT references the primary key of another table, the database has not enforced referential integrity.

In a data model, two main relationship are used :

but you can found other types as :

To describe precisely the type of relationship in a data model, you use the cardinality.

A relationship is a description in a business document that has a verb that relates two entity types:

  • has
  • consists of
  • uses

3 - Natural Language

In a natural language such as English, there are four primary relationships:

  • condition,
  • direction
  • location
  • or time

modelled with the help of preposition.

Verbs provide a link to the condition/state of being of the subject.

coordinating conjunctions indicate the following logical relationship between sentences:

  • reason
  • addition
  • not another option
  • contrast
  • another option
  • contrasting addition
  • result

Adverbial conjunctions indicate the following logical relationship between two sentences, or phrases.

  • Addition
  • Emphasis
  • Comparison or Contrast
  • Cause or Effect
  • Time

4 - Recursive relation

Pretend the recursive relation is between two tables, the real one and a virtual copy.

In this case, a manager table and an employee table.

5 - Binary Relation

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data_modeling/relationship.txt · Last modified: 2017/04/26 13:53 by gerardnico