Neo4j is a graph database. It is an embedded, disk-based, fully transactional Java persistence engine that stores data structured in graphs rather than in tables. A graph (mathematical lingo for a network) is a flexible data structure that allows a more agile and rapid style of development.This graph database has got its own standalone server mode, based on interaction via REST.

1. Neo4J Traversers and Pattern Matchers Ian Robinson http://ianSrobinson.com @ianSrobinson ianSrobinson@gmail.com

2. Traversers

3. Nodes and relationships

4. What does Ian like?

5. What vouchers is Ian entitled to? Including this one?

6. Yes

7. What vouchers is Jim entitled to? Including this one?

8. No

9. VouchersOfInterestQuery public class VouchersOfInterestQuery implements Query<Voucher> { public List<Voucher> execute(final Customer customer, Object... params) { Collection<Node> nodes = customer.getNode() .traverse( Order.DEPTH_FIRST, StopEvaluator.END_OF_GRAPH, new IsVoucherFor(customer), Relationships.PROVIDES, Direction.INCOMING, Relationships.LIKES, Direction.OUTGOING, Relationships.APPLIES_TO, Direction.INCOMING) .getAllNodes(); return toArray(nodes); } private class IsVoucherFor implements ReturnableEvaluator { ... } private class IsSameCustomer implements ReturnableEvaluator { ... } private List<Voucher> toArray(Collection<Node> nodes) { ... } }

10. IsVoucherFor private class IsVoucherFor implements ReturnableEvaluator { private final Customer customer; public IsVoucherFor(Customer customer) { this.customer = customer; } @Override public booleanisReturnableNode(TraversalPositiontp) { if (!isVoucher(tp)) { return false; } if (!isSponsored(tp)) { return true; } Collection<Node> allNodes = tp.currentNode() .traverse( Order.DEPTH_FIRST, StopEvaluator.END_OF_GRAPH, new IsSameCustomer(customer), Relationships.SPONSORS, Direction.INCOMING, Relationships.CUSTOMER_OF, Direction.INCOMING) .getAllNodes(); return allNodes != null && allNodes.size() > 0; } ... }

11. isVoucher private class IsVoucherFor implements ReturnableEvaluator { private final Customer customer; public IsVoucherFor(Customer customer) { this.customer = customer; } @Override public booleanisReturnableNode(TraversalPositiontp) { if (!isVoucher(tp)) { return false; } if (!isSponsored(tp)) { return true; } Collection<Node> allNodes = tp.currentNode() .traverse( Order.DEPTH_FIRST, StopEvaluator.END_OF_GRAPH, new IsSameCustomer(customer), Relationships.SPONSORS, Direction.INCOMING, Relationships.CUSTOMER_OF, Direction.INCOMING) .getAllNodes(); return allNodes != null && allNodes.size() > 0; } ... } private booleanisVoucher(TraversalPositiontp) { return tp.notStartNode() && tp.lastRelationshipTraversed().isType(Relationships.APPLIES_TO); }

12. isSponsored private class IsVoucherFor implements ReturnableEvaluator { private final Customer customer; public IsVoucherFor(Customer customer) { this.customer = customer; } @Override public booleanisReturnableNode(TraversalPositiontp) { if (!isVoucher(tp)) { return false; } if (!isSponsored(tp)) { return true; } Collection<Node> allNodes = tp.currentNode() .traverse( Order.DEPTH_FIRST, StopEvaluator.END_OF_GRAPH, new IsSameCustomer(customer), Relationships.SPONSORS, Direction.INCOMING, Relationships.CUSTOMER_OF, Direction.INCOMING) .getAllNodes(); return allNodes != null && allNodes.size() > 0; } ... } private booleanisSponsored(TraversalPositiontp) { return tp.currentNode().hasRelationship( Relationships.SPONSORS, Direction.INCOMING); }

13. IsSameCustomer private class IsVoucherFor implements ReturnableEvaluator { private final Customer customer; public IsVoucherFor(Customer customer) { this.customer = customer; } @Override public booleanisReturnableNode(TraversalPositiontp) { if (!isVoucher(tp)) { return false; } if(!isSponsored(tp)) { return true; } Collection<Node> allNodes = tp.currentNode() .traverse( Order.DEPTH_FIRST, StopEvaluator.END_OF_GRAPH, new IsSameCustomer(customer), Relationships.SPONSORS, Direction.INCOMING, Relationships.CUSTOMER_OF, Direction.INCOMING) .getAllNodes(); return allNodes != null && allNodes.size() > 0; } ... } private class IsSameCustomer implements ReturnableEvaluator { private final Customer customer; public IsSameCustomer(Customer customer) { this.customer = customer; } @Override public booleanisReturnableNode(TraversalPositiontp) { return tp.currentNode().getId() == customer.getNode().getId(); } }

14. Pattern Matchers

15. Financial products

16. Purchases

17. Recommendations Customers who bought P also bought {Pa, …, Pb} Customers who bought {Pa, …, Pb} also bought {Px, …, Py} Etc Popularity is a function of number of purchasers and distance from original product (products close to the original product are ranked higher than those further away)

18. .2 Customers who bought an ISA also bought…

19. .2 Customers who bought Virgin Card and Fixed Rate Mortgage also bought…

20. Using pattern matchers public Collection<Recommendation> recommend(ProductcurrentProduct, intdepthOfSearch) { HashMap<Long, Recommendation> recommendations = new HashMap<Long, Recommendation>(); Node currentProductNode = currentProduct.getNode(); for(int depth = 1; depth <= depthOfSearch; depth++) { addNodePopularities(recommendations, currentProductNode, depth); } return recommendations.values(); } private void addNodePopularities(HashMap<Long, Recommendation> recommendations, ... }

21. Building subgraph to match private void addNodePopularities(HashMap<Long, Recommendation> recommendations, Node currentProductNode, int depth) { PatternNodefirstProduct = new PatternNode(); PatternNodelastProduct = firstProduct; for(inti = 1; i <= depth; i++) { PatternNodenextProduct = new PatternNode(); PatternNode customer = new PatternNode(); customer.createRelationshipTo(lastProduct, DynamicRelationshipType.withName("Purchased") ); customer.createRelationshipTo(nextProduct, DynamicRelationshipType.withName("Purchased") ); lastProduct = nextProduct; } Iterable<PatternMatch> matches = PatternMatcher.getMatcher().match( firstProduct, currentProductNode); for ( PatternMatch match : matches ) { Node endNode = match.getNodeFor(lastProduct); incrementPopularity(recommendations, currentProductNode, endNode, depth); } } C C P Plast Pfirst