How would one go about storing and querying sparse directed or undirected graphs in Postgresql. There is something like pggraph, but that is still in planning stage.
I realize dedicated graph databases like Neo4J are best suited for this. However is there way to implement same within Postgresql, by using extension or a data type, which would avoid adding another database engine.dtata
At this point I would recommend experimenting with AgensGraph, a promising multimodel distribution of PostgreSQL that offers first class graph databases and queries from both SQL and Cypher. Note that it is a full server, and not an extension like PostGIS, although PostgreSQL extensions can be added to it.
Update:
AgensGraph is now an extension named AGE and was handed over to the Apache foundation.
Since the question is generic, I would add a solution that can work for mostly planar graphs like street networks - PostgreSQL offers an excellent solution through Postgis Topology.
Postgis Topology stores geometries as edges, nodes and faces and their relative relationships. This means that from the geometry of a street network you can select edges and their starting and ending nodes and from this easily build a graph in the processing engine of your choice (networkx or graph-tool for Python are examples).
As I said, though, Postgresql/Postgis Topology works when we want to study geometries like street networks from the perspective of graph analysis.
Use AgensGraph from bitnine.net https://bitnine.net/
And if you want to visualise your graph you can use AgensBrowser also from bitnine
