# 6.2. Preliminary statements

We first introduce some background notions concerning graph databases in section 6.2.1 and then fuzzy set theory in section 6.2.2.

## 6.2.1. *Graph databases*

We present the graph data model in section 6.2.1.1 and explain how to query such a graph database through pattern queries in section 6.2.1.2. We then present the Cypher query language in section 6.2.1.3, which is a concrete language that makes it possible to query a graph database in the Neo4j graph database management system.

### 6.2.1.1. *The graph data model*

A graph database model is a model in which the data structures for the instances and/or the schema are modeled as a directed, possibly labeled graph or generalizations of the graph structure, where data manipulation is expressed by graph-oriented operations and type constructors [ANG 08]. Such a model makes it possible to naturally model networks of entities, where each node is described by a set of characteristics (for instance, a set of attributes) and...