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

The Problem

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

RDBs Use Set Math

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

The Real Solution

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

Graph Examples

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

Audience Participation!

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'; $cypher = new CypherQuery($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

Tools
Neoclipse
Webadmin

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

Questions?

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

by Josh Adell

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