In computing, a graph database is a database that uses graph structures for semantic queries with nodes, edges and properties to represent and store data. A key concept of the system is the graph (or edge or relationship), which directly relates data items in the store. The relationships allow data in the store to be linked together directly, and in many cases retrieved with one operation.
This contrasts with relational databases that, with the aid of relational database management systems, permit managing the data without imposing implementation aspects like physical record chains; for example, links between data are stored in the database itself at the logical level, and relational algebra operations (e.g. join) can be used to manipulate and return related data in the relevant logical format. The execution of relational queries is possible with the aid of the database management systems at the physical level (e.g. using indexes), which permits boosting performance without modifying the logical structure of the database.
They have advantages over relational databases for use cases like social networking, recommendation engines, and fraud detection, where you need to create relationships between data and quickly query these relationships. There are a number of challenges to building these types of applications using a relational database. You would need multiple tables with multiple foreign keys. SQL queries to navigate this data would require nested queries and complex joins that quickly become unwieldy, and the queries would not perform well as your data size grows over time.