Chuck Olson Software Engineer October 2015 Graph Databases and Java 1

Outline  Assumptions  What is a graph and what are they good for?  What is a graph database?  What is Neo4J and how does one use it?  Case: Subway Model Results Compilation  Questions 2

Audience Assumptions Working knowledge of:  Java  Relational databases 3

What is a graph?  Collection of nodes and edges  Edges can be directed (or not)  Edges can represent many things 4 Chuck Jim Jay Gary Knows Coco Annoys

What is a graph? 5

Transportation Example 6 Denver 18:00 20:00 13:00 15:00 12:00 Los Angeles Chicago New York Dallas 16:00 17:00

What are graphs good for?  Often map more directly to the structure of some object-oriented problems.  Work best for storing “richly connected” data  Many algorithms exist to extract useful information – Dijkstra’s shortest path – Minimum spanning tree (Kruskal and others) 7

What is a graph database?  A NoSQL database that stores nodes and edges, and provides a mechanism to easily query information from it.  Can contain nodes of different types  Can have free-form attributes within nodes  Can have edges (relationships) of different types  Can have attributes attached to edges (distance, cost, relationship)  Query mechanism 8

Why would I ever use one?  Easier to find solutions to certain problems by framing data graphically.  “The right tool for the job” 9

Neo4J  Open source (GPLv3 for Community Edition)  V1.0 released in 2010  Written in Java and Scala  Managed by Neo Technology  Uses the Property Graph Model  Embedded or server  Fully transactional  Set of jar files ~30MB  Query language: Cypher 10

How do you use Neo4J?  Creating a database 11 // Location of database String dbPath = “/Users/chuck/myneodb”; GraphDatabaseFactory factory = new GraphDatabaseFactory(); GraphDatabaseBuilder builder = factory.newEmbeddedDatabaseBuilder(dbPath); GraphDatabaseService dbService = builder.newGraphDatabase();

How do you use Neo4J?  Creating fixed node and edge types 12 // Node types public enum NodeLabel implements Label {Station}; // Relationship types public enum RelType implements RelationshipType {TRACKS_TO, ROUTE_TO, AIRWAY_TO};

How do you use Neo4J?  Adding nodes to a database 13 // Create Station node Node node1 = dbService.createNode(NodeLabel.Station); // Set properties on the Station node1.setProperty("number", “100”); node1.setProperty("name", “State St”); // Add another Node node2 = dbService.createNode(NodeLabel.Station); node2.setProperty("number", “101”); node2.setProperty("name", “Lake St”);

How do you use Neo4J?  Adding edges to a database 14 // Create edge from node1 to node2 Relationship edge = node1.createRelationshipTo(node2, RelType.ROUTE_TO); // Set props on the edge edge.setProperty("route", “State St Subway”); edge.setProperty("line", “Red”); // Create another edge of a different type. edge = node1.createRelationshipTo(node2, RelType.TRACK_TO);

How do you use Neo4J?  Querying the database 15 // Returns station numbers of all stations in graph. String queryText = “MATCH (stn:Station) RETURN stn.number"; ExecutionEngine engine = new ExecutionEngine(dbService); ExecutionResult result = engine.execute(queryText); Iterator stnIt = result.columnAs("stn.number"); // Print results while (stnIt.hasNext()) System.out.println(stnIt.next());

Case: Studying Subways 16

Case: Studying Subways Questions we might want to ask:  “Find all the stations that have air connectivity paths to station X that are less than K km”  “Find all the train routes that that go through all stations that are N stops from station X” 17

Case: Studying Subways 18

Case: Studying Subways 19 Stations - Number (id) - Name - Lat - Lon Segments - SegmentId (id) - StationFromNumber - StationToNumber - Length - SegmentType SegmentTypes - SegmentTypeId (id) - TypeName LineSegments - LineId (id) - SegmentId - SegmentIndex Lines - LineId (id) - LineName - LineDirection Relational attempt…

Case: Studying Subways 20 Station Name Station Number Route Name Distance Graph attempt… Node ROUTE_TO Edge TRACKS_TO Edge AIRWAY_TO Edge

Case: Studying Subways 21 St. Paul’s 100 Bank 101 Cannon Street 200 Monument 201 Tower Hill 202 Tower Gateway 300 Red Green Yellow 1 km.7 km.2 km 1.8 km Green Yellow.1 km White/Blue

Case: Studying Subways  Answering the question: returns all stations 2 track segments from station 200 (Cannon Street) 22 MATCH p=(fromStn:Station)-[edge:TRACKS_TO*2..2]- (toStn:Station {number:‘200’}) WHERE fromStn.number <> toStn.number RETURN distinct fromStn,toStn,fromStn.number

Drawbacks  No standard query language like SQL. Vendor-specific.  Query language learning curve.  Lack of built-in visualization tools. 23

For Further Reading… 24 Ian Robinson, Jim Webber, Emil Eifrem Graph Databases, 2 nd Edition O’Reilly and Associates Rik Van Bruggen Learning Neo4J Packt Publishing

Questions 25