Graph Database Overview

Changes in database technology

Changes in database technology from a historical perspective that show how graph thinking emerged.

1960s: hierarchical
1980s: relational
2000s: NoSQL
2020s: graph thinking

Introduction to graph databases

Graph data is based on mathematical graph theory. It consists of points (Node/Vertex) that represent data for individual objects, groups (Label) of objects with similar characteristics, and lines (Edge) that represent relationships between objects.

graph-database
The concept of a graph that shows human relationships with points and lines

Graph theory terms

Let’s look at terms used in graph theory.

Types of graphs

Term	Description
Graph	A data structure that organizes relationships between things as Nodes and Edges
Directed Graph	A graph whose Edges between Nodes have direction
Undirected Graph	A graph whose Edges between Nodes have no direction, where the relationship between two Nodes is bidirectional
Weighted Graph	A graph whose Edges between Nodes have weights
Unweighted Graph	A graph whose Edges between Nodes have no weights, where all Edges have equal strength

Resources in Graph

Term	Description
Node	An entity in ontology
Edge	A relation in ontology
Properties	Information related to Nodes and Edges
Label	A Role in ontology

What is ontology?

An ontology is a model that represents, in a conceptual and computer-processable form, what people have agreed on through discussion about what they see, hear, feel, and think about the world. It explicitly defines concept types and usage constraints. Source: [Wiki](https://ko.wikipedia.org/wiki/%EC%98%A8%ED%86%A8%EB%A1%9C%EC%A7%80)

Properties on Node: Node properties

Term	Description
title	Node name
caption	Node description

:Properties on Edge: Edge properties

Term	Description
Directionality	Connection direction
Weight	Connection weight

Data collection

Term	Description
Node List	A list of all Nodes
Edge List	A list of all Edges
Adjacency Matrix	A two-dimensional table of all Nodes x all Nodes. Each entry represents the Edge state numerically. Example: -1 means no connection, 1 to N means Weight.
Neighbors	A list of Nodes adjacent to a Node