Intro to Cypher

(Neo4j)-[: ]->Cypher
Michael Hunger - Neo Technology

1

(Michael) -[:WORKS_ON]-> (Neo4j)
console

Cypher community
graph
Community

ME

Server

Spring Cloud

2

We're talking about a
Property Graph

7

Property Graph

Nodes

7

Property Graph

Nodes

Relationships

7

Property Graph
Em Joh
il a n
knows knows
Alli Tob Lar

Nodes
son ias knows s
knows
And And knows
knows rea rés
s
knows knows knows
Pet Miic
Mc knows Ian
er knows a
a
knows knows
De Mic
lia h ael

Relationships

Properties (each a key+value)

+ Indexes (for easy look-ups)
7

(Neo4j) -[:IS_A]-> (Graph Database)
Lucene
Sharding 1 M/s

Master/
Index

LS
Slave

TRAVERSA
HIG
TES
H_A
VA RA
G
IL. TE
IN
PROVIDES ACID
Server RUN
S_A LI TX
S CE
NS
ED
_L
ES_T
Ruby IK

RU
JS E
MySQL
S
_A

NS
SC AL

O

Clojure

_O
NS

.net
RU

N Mongo
34bn
embedded Heroku
Nodes 9

How do you query this
graph database?

10

With a Graph Query
Language:
Cypher

11

What is Cypher?
๏Pattern-Matching Query Language
๏Humane language
๏Expressive
๏Declarative: Say what you want, not how
๏borrows from well known query langs
๏Aggregation, Ordering, Limit
๏Update the Graph

12

Something new? Why?
๏ Existing Neo4j query mechanisms were not simple enough
• Too verbose (Java API)
• Too prescriptive (Gremlin)
๏ SQL: Unable to express paths
• these are crucial for graph-based reasoning
• Neo4j is schema/table free
๏ SPARQL: designed for a different data model
• namespaces
• properties as nodes
13

A Graph
Can‘t see the Patterns for the Trees

http://maxdemarzi.com/2012/02/13/visualizing-a-network-with-cypher/

14

It‘s all about Patterns

A

B C

We want to ﬁnd this Pattern!
15

Patterns in a Graph

16

Patterns as ASCII-ART

21

Patterns as ASCII-ART

() --> ()
21

Named Nodes

A B

22

Named Nodes

A B

(A) --> (B)

22

Named Directed Rels
LOVES
A B

23

Named Directed Rels
LOVES
A B

A -[:LOVES]-> B

23

Paths

A B C

A --> B --> C

24

Cyclic-Path-Patterns
A

B C

25

A

B C

A --> B --> C, A --> C

25

A

B C

A --> B --> C, A --> C
A --> B --> C <-- A
25

Variable Length Paths
A B

A B

A B

...
A -[*]-> B 26

Optional Relationships

A B

27

Optional Relationships

A B

A -[?]-> B

27

How does it work?

28

How does it work?
// lookup starting point in an index
start n=node:People(name = ‘Andreas’)

And
rea
s

28

How does it work?
// lookup starting point in an index
then traverse to find results
start n=node:People(name = ‘Andreas’)
match (n)--()--(foaf) return foaf

And
rea
s

28

The Parts of Cypher

29

Cypher: START + RETURN
๏ START <lookup> RETURN <expressions>
๏ START binds terms using simple look-up
•directly using known ids
•or based on indexed Property
๏ RETURN expressions specify result set

30

Cypher: START + RETURN
๏ START <lookup> RETURN <expressions>
๏ START binds terms using simple look-up
•directly using known ids
•or based on indexed Property
๏ RETURN expressions specify result set
// lookup node id 0, return that node
start n=node(0) return n
// lookup node in Index, return that node
start n=node:Person(name="Andreas") return n
// lookup all nodes, return all name properties
start n=node(*) return n.name

30

Cypher: MATCH
๏ START <lookup> MATCH <pattern> RETURN <expr>
๏ MATCH describes a pattern of nodes+relationships
•node terms in optional parenthesis
•lines with arrows for relationships

31

Cypher: MATCH
๏ START <lookup> MATCH <pattern> RETURN <expr>
๏ MATCH describes a pattern of nodes+relationships
•node terms in optional parenthesis
•lines with arrows for relationships
// lookup 'n', traverse any relationship to some 'm'
start n=node(0) match (n)--(m) return n,m
// any outgoing relationship from 'n' to 'm'
start n=node(0) match n-->m return n,m
// only 'KNOWS' relationships from 'n' to 'm'
start n=node(0) match n-[:KNOWS]->m return n,m
// from 'n' to 'm' and capture the relationship as 'r'
start n=node(0) match n-[r]->m return n,r,m
// from 'n' outgoing to 'm', then incoming from 'o'
start n=node(0) match n-->m<--o return n,m,o
31

Cypher: RETURN
๏ RETURN <expressions>, aggregation(expr) as alias
๏ RETURN nodes, rels, properties
๏ RETURN expressions of functions and operators
๏ RETURN aggregation functions on the above

32

Cypher: RETURN
๏ RETURN <expressions>, aggregation(expr) as alias
๏ RETURN nodes, rels, properties
๏ RETURN expressions of functions and operators
๏ RETURN aggregation functions on the above

// aggregate on n, count the m‘s
start n=node(0) match n--m return n,count(*)
// alias n.name as name
start n=node(0) return n.name as name
// aggregate m‘s into list
start n=node(*) match n--m return n,collect(m)
// filter m‘s by name
start n=node(*) match n--m return n,filter(x in collect(m):
m.name ˜= /A.*/) as a_block
32

Cypher: WHERE
๏ START <lookup> [MATCH <pattern>]
WHERE <condition> RETURN <expr>
๏ WHERE ﬁlters nodes or relationships
•uses expressions to constrain elements

33

Cypher: WHERE
๏ START <lookup> [MATCH <pattern>]
WHERE <condition> RETURN <expr>
๏ WHERE ﬁlters nodes or relationships
•uses expressions to constrain elements
// lookup all nodes as 'n', constrained to name 'Andreas'
start n=node(*) where n.name='Andreas' return n
// filter nodes where age is less than 30
start n=node(*) where n.age<30 return n
// filter using a regular expression
start n=node(*) where n.name =~ /Tob.*/ return n
// filter for a property exists
start n=node(*) where has(n.name) return n

33

Cypher: CREATE
๏ CREATE <node>[,node or relationship] RETURN <expr>
•create nodes with optional properties
•create relationship (must have a type)

34

Cypher: CREATE
๏ CREATE <node>[,node or relationship] RETURN <expr>
•create nodes with optional properties
•create relationship (must have a type)

// create an anonymous node
create n
// create node with a property, returning it
create n={name:'Andreas'} return n
// lookup 2 nodes, then create a relationship and return it
start n=node(0),m=node(1) create n-[r:KNOWS]-m return r
// lookup nodes, then create a relationship with properties
start n=node(1),m=node(2) create n-[r:KNOWS {since:2008}]->m

34

Cypher: CREATE UNIQUE
๏ CREATE UNIQUE node-[rel]->(node {prop : value})
•„ﬁxes“ the graph
•starts at bound nodes, properties rels and nodes by
comparing types and
tries to ﬁnd

•if not found creates them

35

Cypher: CREATE UNIQUE
๏ CREATE UNIQUE node-[rel]->(node {prop : value})
•„ﬁxes“ the graph
•starts at bound nodes, properties rels and nodes by
comparing types and
tries to ﬁnd

•if not found creates them
// create a new relationship
start n=.., m=.. create unique n-[:KNOWS]->m
// create a new node AND relationship
start n=... create unique n-[:TAGGED]->(tag {name:“neo“})
// matches the tag node by name only creates new relationship
start n=... create unique n-[:TAGGED]->(tag {name:“neo“})

35

Cypher: SET
๏ SET [<node property>] [<relationship property>]
•update a property on a node or relationship
•must follow a START

36

Cypher: SET
๏ SET [<node property>] [<relationship property>]
•update a property on a node or relationship
•must follow a START

// update the name property
start n=node(0) set n.name='Peter'
// update many nodes, using a calculation
start n=node(*) set n.size=n.size+1
// match & capture a relationship, update a property
start n=node(1) match n-[r]-m set r.times=10

36

Cypher: DELETE
๏ DELETE [<node>|<relationship>|<property>]
•delete a node, relationship or property
•toall relationships must be deleted ﬁrst
delete a node,

37

Cypher: DELETE
๏ DELETE [<node>|<relationship>|<property>]
•delete a node, relationship or property
•toall relationships must be deleted ﬁrst
delete a node,

// delete a node
start n=node(5) delete n
// remove a node and all relationships
start n=node(3) match n-[r]-() delete n, r
// remove a property
start n=node(3) delete n.age

37

More Advanced
Examples

38

START user = node(1)
MATCH user -[user_skill]-> skill
RETURN skill, user_skill
SELECT skills.*, user_skill.*
FROM users
JOIN user_skill ON users.id = user_skill.user_id
JOIN skills ON user_skill.skill_id = skill.id WHERE users.id = 1

39

Example:
Old, Influential Friends
START me = node(...)
MATCH (me) - [f:FRIEND] - (old_friend)
- [:FRIEND ] - (fof)
WHERE ({today}-f.begin) > 365*10

WITH old_friend, collect(fof.name) as names

WHERE length(names) > 100
RETURN old_friend, names
ORDER BY old_friend.name ASC
f:FRIEND :FRIEND
me friend fof

Example:
Simple Recommendation
START me = node(...)
MATCH (me) -[r1:RATED ]->(thing)
<-[r2:RATED ]- (someone)
-[r3:RATED ]->(cool_thing)
WHERE ABS(r1.stars-r2.stars) <= 2
AND r3.stars > 3
RETURN cool_thing, count(*) AS cnt
ORDER BY cnt DESC LIMIT 10
r1:RATED thing r2:RATED
me so
TED
r 3: RA
cool
thing 41

Cypher Cheat Sheet
http://neo4j.org/resources/cypher

42

The Rabbithole

http://console.neo4j.org
This Graph: http://tinyurl.com/7cnvmlq
43

How to use Cypher
in YOUR programs

44

Neo4j API
ExecutionEngine engine = new ExecutionEngine(graphDB);

String query = „start n=node:Person(name={name})
match n-[:ACTS_IN]->movie<-[:ACTS_IN]-friend
return friend“;
ExecutionResult result = engine.query(query, map(„name“, „Keanu“);

for (Map<String,Object> row : result) {
Node friend = row.get(„friend“);
}

Iterator<Node> friends = result.columnAs(„friend“);

http://bit.ly/cypher-queries

45

How to get started?

46

How to get started?
๏ Documentation

46

How to get started?
๏ Documentation
• docs.neo4j.org - tutorials+reference

46

How to get started?
๏ Documentation
• http://console.neo4j.org

46

How to get started?
๏ Documentation
• Neo4j in Action

46

How to get started?
๏ Documentation
• Neo4j in Action
• Good Relationships

46

How to get started?
๏ Documentation
• Neo4j in Action
๏ Get Neo4j

46

How to get started?
๏ Documentation
• Neo4j in Action
๏ Get Neo4j
• http://neo4j.org/download

46

How to get started?
๏ Documentation
• Neo4j in Action
๏ Get Neo4j
• http://addons.heroku.com/neo4j/
๏ Participate
• http://groups.google.com/group/neo4j
• http://neo4j.meetup.com
46

How to get started?
๏ Documentation
• Neo4j in Action
๏ Get Neo4j
• http://addons.heroku.com/neo4j/
๏ Participate
• http://groups.google.com/group/neo4j
• http://neo4j.meetup.com
• a session like this one ;)
46

http://console.neo4j.org/r/GoT
https://dl.dropbox.com/u/14493611/got.txt
47

Neo4j-JDBC Driver & MovieDB Dataset

http://blog.neo4j.org/2012/06/wanted-your-
help-in-testing-neo4j-jdbc.html
48

Got a Conference? Need a Dataset?

http://blog.neo4j.org/2012/08/at-conference-
need-dataset-neo4j-at.html
49

Neo4j in Action
Software Metrics

50

Graphs in Software Technolgoy
๏ UML Diagrams are graphs
๏ dependencies between classes, packages, modules etc are graphs
๏ Software Metrics use dependency analysis
๏ Visualizations
๏ Cyclomatic Complexity,
๏ Fan-in (afferent-coupling) / Fan-out (efferent coupling) etc.

51

Class Diagram is a Graph

53

But there is more
๏Visualize & query Method, Field
dependencies
๏Collaborative ﬁltering (co-usage)
๏Ranking
๏God classes
๏Paths between classes

55

Welcome to Class-Graph
๏take a JAR
๏put it under ASM
๏scan it superfast
๏pull everything into Neo4j
๏add categories, indexes
๏Have Fun

http://github.com/jexp/class-graph 56

Welcome to Class-Graph

57

Interactive Hands-On Session
๏Lots of tasks
๏use Cypher to solve them
http://neo4j.org/resources/cypher
๏be creative, work together
๏ask !
๏Server http://bit.ly/innoq-neo4j
๏just the beginning
58

Task: Find java.lang.Number and return it

59

Task: Find java.lang.Number and return it

START o=node:types(name="java.lang.Number")
RETURN o;

59

Task: Subclasses of Number?

•Return just the name
•Order them alphabetically

60

Task: Subclasses of Number?

START n=node:types(name="java.lang.Number")
MATCH n<-[:SUPER_TYPE]-s
RETURN s.name
ORDER BY s.name;

•Return just the name
•Order them alphabetically

60

Task: Which Methods does it have / how many

•Find the top 5 classes with the most members

61

Task: Which Methods does it have / how many

START n=node:types(name="java.lang.Number")
MATCH n-[:METHOD_OF|FIELD_OF]->m
RETURN m;

•Find the top 5 classes with the most members

61

Task: Calculate the fan-out of
java.lang.StringBuilder

•Calculate fan-in
•Which class has the highest fan-out
•What about package-level? 62

Task: Calculate the fan-out of
java.lang.StringBuilder
START o=node:types(name="j.l.StringBuilder")
MATCH o-[:FIELD_OF]->f-[:FIELD_TYPE]->tf,
o-[:METHOD_OF]->m-[:PARAM_TYPE]->tp,
m-[:RETURN_TYPE]->tr
RETURN o,count(distinct tf)
+ count(distinct tp)
+ count(distinct tr) as fan_out;

•Calculate fan-in
•Which class has the highest fan-out
•What about package-level? 62

Task: Find longest Inheritance Path

63

Task: Find longest Inheritance Path

start c=node:types(name="java.lang.Object")
match path=p<-[:SUPER_TYPE*]-c
return extract(n in nodes(path) : n.name),
length(path) as len
order by len desc
limit 5;

63

Task: Find the class that used IOException
most often

64

Task: Find the class that used IOException
most often

START ex=node:types(name="java.io.IOException"
MATCH ex<-[:THROWS]-m<-[:METHOD_OF]-c
RETURN c, count(*)
ORDER BY count(*)
LIMIT 5;

64

Task: Which other classes did classes that
threw IOException use most often?

•What could be a source of IOExceptions
65

Task: Which other classes did classes that
threw IOException use most often?
START ex=node:types(name="java.io.IOException")
MATCH ex<-[:THROWS]-m<-[:METHOD_OF]-c,
mbr<-[:METHOD_OF|FIELD_OF]-c,
mbr-[:FIELD_TYPE|PARAM_TYPE|
RETURN_TYPE|THROWS]->other_type
WHERE other_type.name =~ /.+[.].+/
RETURN other_type.name, count(*)
ORDER BY count(*) desc
LIMIT 10;
•What could be a source of IOExceptions
65

Task: Find a class you like and add a ﬁeld with
your name and some type

66

Task: Find a class you like and add a ﬁeld with
your name and some type
START c=node:types(name="void"),
t=node:types(name="java.lang.reflect.Proxy")
CREATE c-[:FIELD_OF]->(field {name:“Michael“})
-[:FIELD_TYPE]->t;

66

Task: Delete the most annoying class and all its
methods, ﬁelds and their relationships

67

Task: Delete the most annoying class and all its
methods, ﬁelds and their relationships
START c=node:types(name="java.awt.List"),
MATCH c-[r1:FIELD_OF|METHOD_OF]->mbr-[r2]-()
c-[r]-()
DELETE c,mbr,r1,r2,r;

67

Intro to Cypher

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Intro to Cypher

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