Graph Databases

Graph Databases Josh Adell <josh.adell@gmail.com> 20110719

Who am I? Software developer: PHP, Javascript, SQL http://www.dunnwell.com Fan of using the right tool for the job

Find Every Actor at Each Degree > -- First degree > SELECT actor_name FROM cast WHERE movie_title IN (SELECT DISTINCT movie_title FROM cast WHERE actor_name='Kevin Bacon') > -- Second degree > SELECT actor_name FROM cast WHERE movie_title IN (SELECT DISTINCT movie_title FROM cast WHERE actor_name IN (SELECT actor_name FROM cast WHERE movie_title IN (SELECT DISTINCT movie_title FROM cast WHERE actor_name='Kevin Bacon'))) > -- Third degree > SELECT actor_name FROM cast WHERE movie_title IN(SELECT DISTINCT movie_title FROM cast WHERE actor_name IN (SELECT actor_name FROM cast WHERE movie_title IN (SELECT DISTINCT movie_title FROM cast WHERE actor_name IN (SELECT actor_name FROM cast WHERE movie_title IN (SELECT DISTINCT movie_title FROM cast WHERE actor_name='Kevin Bacon'))))

The Truth Relational databases aren't very good with relationsh ips Data RDBMs

The Real Problem Finding relationships across multiple degrees of separation ...and across multiple data types ...and where you don't even know there is a relationship

Computer Science Definition A graph is an ordered pair G = (V, E) where V is a set of vertices and E is a set of edges , which are pairs of vertices.

Some Graph DB Vocabulary Node : vertex Relationship : edge Property : meta-datum attached to a node or relationship Path : an ordered list of nodes and relationships Index : node or relationship lookup table

Relationships are First-Class Citizens Have a type Have properties Have a direction Domain semantics Traversable in any direction

Relational Databases are Graphs!

New Solution to the Bacon Problem $keanu = $actorIndex->find('name', 'Keanu Reeves'); $kevin = $actorIndex->find('name', 'Kevin Bacon'); $path = $keanu->findPathTo($kevin);

Some Graph Use Cases Social networking Manufacturing Map directions Fraud detection Multi-tenancy

Modelling a Domain with Graphs Graphs are "whiteboard-friendly" Nouns become nodes Verbs become relationships Properties are adjectives and adverbs

Neo Technologies http://neo4j.org Embedded in Java applications Standalone server via REST Plugins: spatial, lucene, rdf http://github.com/jadell/Neo4jPHP

Using the REST client $client = new Client(new Transport()); $customer = new Node($client); $customer->setProperty('name', 'Josh')->save(); $store = new Node($client); $store->setProperty('name', 'Home Despot') ->setProperty('location', 'Durham, NC')->save(); $order = new Node($client); $order->save(); $item = new Node($client); $item->setProperty('item_number', 'Q32-ESM')->save(); $order->relateTo($item, 'CONTAINS')->save(); $customer->relateTo($order, 'BOUGHT')->save(); $store->relateTo($order, 'SOLD')->save(); $customerIndex = new Index($client, Index::TypeNode, 'customers'); $customerIndex->add($customer, 'name', $customer->getProperty('name')); $customerIndex->add($customer, 'rating', 'A++');

Graph Mining Paths Traversals Ad-hoc Queries

Path Finding Find any connection from node A to node B Limit by relationship types and/or direction Path finding algorithms: all, simple, shortest, Dijkstra $customer = $customerIndex->findOne('name', 'Josh'); $item = $itemIndex->findOne('item_number', 'Q32-ESM'); $path = $item->findPathsTo($customer) ->setMaxDepth(2) ->getSinglePath(); foreach ($path as $node) { echo $node->getId() . "\n"; }

Traversal Complex/Custom path finding Base next decision on previous path $traversal = new Traversal($client); $traversal ->setOrder(Traversal::OrderDepthFirst) ->setUniqueness(Traversal::UniquenessNodeGlobal) ->setPruneEvaluator('javascript','(function traverse(pos) { if (pos.length() == 1 && pos.lastRelationship.getType() == "CONTAINS") { return false; } else if (pos.length() == 2 && pos.lastRelationship.getType() == "BOUGHT") { return false; } return true;})(position)') ->setReturnFilter('javascript', 'return position.endNode().getProperty('type') == 'Customer;'); $customers = $traversal->getResults($item, Traversal::ReturnTypeNode);

Uses mathematical notation approach Complex traversal behaviors, including backtracking https://github.com/tinkerpop/gremlin/wiki m = [:] g.v(1).out('likes').in('likes').out('likes').groupCount(m) m.sort{a,b -> a.value <=> b.value}

Cypher "What to find" vs. "How to find" $query = 'START item=(1) MATCH (item)<-[:CONTAINS]-(order)<-[:BOUGHT]-(customer) RETURN customer'; $cypher = new Cypher\Query($client, $query); $customers = $cypher->getResultSet();

Cypher Syntax START item = (1) START item = (1,2,3) START item = (items, 'name:Q32*') START item = (1), customer = (2,3) MATCH (item)<--(order) MATCH (order)-->(item) MATCH (order)-[r]->(item) MATCH ()--(item) MATCH (supplier)-[:SUPPLIES]->(item)<-[:CONTAINS]-(order), (customer)-[:RATED]->(item) WHERE customer.name = 'Josh' and s.coupon = 'freewidget' RETURN item, order RETURN customer, item, r.rating RETURN r~TYPE RETURN COUNT(*) ORDER BY customer.name DESC RETURN AVG(r.rating) LIMIT 3 SKIP 2

Cypher - All Together Now // Find the top 10 `widget` ratings by customers who bought AND rated // `widgets`, and the supplier START item = (items, 'name:widget') MATCH (item)<--(order)<--(customer)-[r:RATED]->(item)<--(supplier) RETURN customer, r.rating, supplier ORDER BY r.rating DESC LIMIT 10

Are RDBs Useful At All? Aggregation Ordered data Truly tabular data Few or clearly defined relationships

Resources http://neo4j.org http://docs.neo4j.org http://www.youtube.com/watch?v=UodTzseLh04 Emil Eifrem (Neo Tech. CEO) webinar Check out around the 54 minute mark http://github.com/jadell/Neo4jPHP http://joshadell.com [email_address] @josh_adell Google+, Facebook, LinkedIn

Graph Databases

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