When new segment titled Graph Database was born, it wasn’t Relational Database and is classed as NoSQL, but it wasn’t same with Key-Value Store or Document Store. So a category as ‘Graph Data Model’ was created.

A graph is to represent a relationship between nodes by three elements of node, relation, feature and it can explain graph data model. So, we have a question how graph data model was created once it was created.

There is ‘Open Graph’ of Facebook and graph database of LinkedIn besides product of vendors such as Neo4j. Also, RDF (Resource Description Framework) used at Linked Open data and Google’s Knowledge Graph are using a graph data model.

▲ Figure 1. Google’s Knowledge Graph

▲ Figure 2. Resource Description Framework

Not only SNS specialized in a relationship, but also communication network, power grid, etc. are similar to graph data model and suitable for graph database ultimately. In addition, an optimal path in a map informs us about the suitability of graph database. A person agonized the question in the 18th century and proved it by formulating ‘Graph Theory’.

The question is just ‘Seven Bridges of Königsberg’. Königsberg is a home city of Immanuel Kent, a famous philosopher with Pregel River. The problem was to devise a walk through the city that would cross each bridge once and only once, with the provisos that: the islands could only be reached by the bridges and every bridge once accessed must be crossed to its other end. The starting and ending points of the walk need not be the same.

▲ Figure 3. Seven Bridges of Königsberg’

Leonhard Euler, a famous mathematician, pointed out that the choice of route inside each land mass is irrelevant. The only important feature of a route is the sequence of bridges crossed. This allowed him to reformulate the problem in abstract terms (laying the foundations of graph theory), eliminating all features except the list of land masses and the bridges connecting them.

▲ Figure 4. A model of Graph Theory

An application of this graph theory is graph data model, and Dealing with database by drawing it to storage-level is Graph Database.

**BITNINE GLOBAL INC., THE COMPANY SPECIALIZING IN GRAPH DATABASE**

비트나인, 그래프 데이터베이스 전문 기업