What are knowledge graphs? When would you need a knowledge graph over say a database to store information?

A knowledge graph organizes real world knowledge as entities and relationships between entities. Creating a knowledge graph often involves scraping / ingesting unstructured data and creating structure out of it by extracting entities and relationships automatically. Examples of knowledge graphs are Wordnet, DBpedia,..

 

A database also is a knowledge graph in some sense. Since it realizes edges between different nodes (through foreign keys). But a graph data structure is useful for many operations not realised efficiently through a typical db join. Example: Get all my friends in my 2-deep neighbourhood and aggregate their preferences of color.  In a typical relational database, relationships are defined at a table level, while in a graph database, there is more flexibility and relationships can be unique to a node.

More Resources:

https://hackernoon.com/wtf-is-a-knowledge-graph-a16603a1a25f

https://www.infoworld.com/article/3263764/database/what-is-a-graph-database-a-better-way-to-store-connected-data.html

 

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