GraphDBs & Neo4J

@lifeistooshort

What We Will Learn

  • What is Graph Theory
  • Why should I use a GraphDB
  • What is Neo4J and how is it used

Best Resource I Have Found

What is a Graph?

Definition

"A collection of vertices and edges that join pairs of vertices"

In Neo4J this means Nodes and Relationships

The definition is G(V,E)

2|E|=Σdeg(v)

Not Just For Computer Science

Cartography

Electrical Engineering

Physics

Biology

Leonhard Euler

Seven Bridges of Königsberg

Eulerian Path

All bridges are crossed once and only once

Eulerian Circuits start and stop on same node

Depends on Degrees (0 or 2 odd)

Zombieland

Bill Murray

Bill Murray

ACTS_IN

ACTS_IN

Directed vs Non-Directed

Non-directed graphs do not have a start or end node.

We can also weight these relations

Directed graphs allow for a direction in a relationship.

Advantages

Graphs can morph into many views

Great for inferring relationships

Quickest way to find related nodes

Why Use a GraphDB?

Relational DBs

Tried and true technology for highly structured data.

Joins use keys

May require mapping tables

Finding friends of friends becomes memory intensive

Non-Native storage translates from relational to graph

Example Using Relational

SELECT p1.Person AS PERSON, p2.Person AS FRIEND_OF_FRIEND
FROM PersonFriend pf1 JOIN Person p1
ON pf1.PersonID = p1.ID
JOIN PersonFriend pf2
ON pf2.PersonID = pf1.FriendID
JOIN Person p2
ON pf2.FriendID = p2.ID
WHERE p1.Person = 'Alice' AND pf2.FriendID <> p1.ID

NoSQL DBs

Describes storing data as documents, columns, key-value pairs and more

Less rigid

Can create a relationship by storing a document's ID field

Now the application is responsible for joins (map-reduce)

Graph DBs

Can create models that more closely resemble the domain

Relationships are first-class citizens

No need to match means less resource usage

Use Native Storage

Cypher

Store Files

Nodes 9 bytes, Relationships are 33

IDs are based on position (exp 100*9)

InUse is like a delete field

Traversal

Graph Techniques

"They (graph techniques) are especially useful when we want to gain insight into a new domain--or even understand what kind of insight it's possible to extract from a domain" -- Graph Databases

Depth Search

Pop items on stack till there is no place to go. Then we pop off

 

Once the stack is empty we are done.

Breadth Search

All related nodes are added to a queue. 

 

After all related nodes are visited the base node is popped off the queue.

Triadic Closures

Graphs In The Wild

  • Social
  • Geo-spatial
  • Recommendations
  • Access Control

Other Types of Graphs

  • Property Graph
    • Node contains properties
  • Hypergraph
    • Relationship can connect n nodes
  • Triples

And of course...

What is Neo4J?

Java based GraphDB

Native & REST Interfaces

Server & Embedded Versions

Supports Scaling and Sharding

Advantage

Index-free adjacency allows for millisecond response.

Reduces object-relational impedance mismatch 

Easy to change and adapt

ACID

Disadvantages

You still want a relational store

Memory is more expensive than space

Lack of developers

Almost Forgot

It Is Open Source!

Steps to set it up

Download Neo4J

Default port is 7474

Run Neo4J just like Tomcat

You can add JAX-RS endpoints

Ways to interact with Neo4J

Kernel

Listen directly for transactions

Only called on write transactions that will be commited

Can be used to prevent physical deletions

Java-Based

Core

Allows for imperative declaration

Java-Based

Relationships are only traversed when accessed

You will need domain info in code

 

// Index lookup for the node representing the doctor is omitted for brevity

Iterable<Relationship> relationships = doctor.getRelationships(Direction.INCOMING, COMPANION_OF );

for ( Relationship rel : relationships )

{

  Node companionNode = rel.getStartNode();

  if ( companionNode.hasRelationship( Direction.OUTGOING, IS_A ) )

  {

    Relationship singleRelationship = companionNode.getSingleRelationship( IS_A, Direction.OUTGOING );

    Node endNode = singleRelationship.getEndNode();

    if ( endNode.equals( human ) )

    {

      // Found one!

    }

  }

}

Traverse

Java-Based

Used to gain specific control over traversals

Declarative Interface

You can fall back to the Core APIs

Cypher

Accessible Via Java or REST

Typically results in JSON

Query language

Most common way to interface

Demo Time!

MATCH

Match reads nodes/relationships

CREATE

Creates a nodes/relationships

MERGE

Creates nodes/relationships if none exist, otherwise it updates the existing one

Delete

Removes nodes/relationships

MATCH

CREATE

MERGE

DELETE

GET

POST

PUT

DELETE

Review

  • Graphs are a way to express data in nodes and relationships.
  • GraphDBs provide the ability to graph data natively.
  • Neo4J is a GraphDB that provides a powerful query language Cipher

Questions?

Links and More Info

JackieRGleason.com

neo4j.com/graphacademy

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