Source code analysis is full of graphs: abstract syntax trees, control flow graphs, call graphs, program dependency graphs and directory structures, to name a few. Joern analyzes a code base using a robust parser for C/C++ and represents the entire code base by one large property graph stored in a Neo4J graph database. This allows code to be mined using complex queries formulated in the graph traversal languages Gremlin and Cypher.
The documentation can be found here